SingleStore DB

List of Engine Variables

The following tables list the sync engine variables and non-sync engine variables. Some variables have an in-depth description that supplements the description found in the table.

Sync Variables List

See the engine variables overview to learn how sync variables work.

All of the sync variables listed in the following table are global variables, except when noted as a session variable that can also be set globally in the Description column.

You can set sync variables on the master aggregator, only. After you set a sync variable, the nodes affected by your update (all aggregators, all leaves, or both) depend on the variable’s type and the command you use to set the variable. Each variable’s type is indicated in the last sentence in the Description column in the following table.

Name

Description

Default

aggregator_failure_detection

Deprecated in MemSQL 6.0, this is the timeout used when gathering workload management statistics from leaves. This variable can sync to all aggregators.

ON

auto_attach

Specifies if the aggregator will try to attach a node automatically after it has been marked offline, but starts responding to heartbeats again. This variable can sync to all aggregators.

ON

attach_rebalance_delay_seconds

Number of seconds to wait after a new node has attached to the cluster before running a rebalance. This mechanism is used to batch up rebalancing if many nodes fail and then come back online within a short period of time. This variable can sync to all aggregators.

120

background_statistics_collection_interval

How often in seconds background statistics will check for out of date statistics (rowstore only). This variable can sync to all aggregators.

60

background_statistics_collection_threshold

Threshold as a fraction of table row count triggering the collection of autostatistics. This variable can sync to all aggregators.

0.5

cardinality_estimation_level

Possible values are '6.0', '6.5', '7.0', '7.1', and '7.3'. The behavior of each setting follows: '6.0': Use legacy histograms; '6.5': Use advanced histograms; '7.0': Same use of histograms as 6.5; '7.0': Use histograms for join estimation; '7.3': Use sampling and histograms together (when both are available), to improve selectivity estimation.

'7.1'

change_count_write_interval

Maximum frequency in seconds that change count metadata will be written. Will never occur more frequently than background_statistics_collection_interval. This variable can sync to all aggregators.

1200

character_set_server

The character set of the node. This is a session variable that can also be set globally. This variable can sync to all nodes, including aggregator and leaf nodes. For more information on this variable, see the In-Depth Variable Definitions section below.

utf8

cluster_name

Specifies the cluster name used by the backup.

collation_connection

Sets the collation that is used on the node. When you set this variable, collation_database and collation_server are automatically set to the same value. For more information on this variable, see the In-Depth Variable Definitions section below. This is a session variable that can also be set globally. This variable can sync to all aggregators and all leaves.

utf8_general_ci

collation_database

Sets the collation that is used on the node. When you set this variable, collation_connection and collation_server are automatically set to the same value. For more information on this variable, see the In-Depth Variable Definitions section below. This is a session variable that can also be set globally. This variable can sync to all aggregators and all leaves.

utf8_general_ci

collation_server

Sets the collation that is used on the node. When you set this variable, collation_connection and collation_database are automatically set to the same value. For more information on this variable, see the In-Depth Variable Definitions section below. This is a session variable that can also be set globally. This variable can sync to all aggregators and all leaves.

utf8_general_ci

columnstore_disk_insert_threshold

At this threshold (fraction of columnstore_flush_bytes), INSERT, LOAD DATA, and UPDATE queries to the columnstore will write straight to disk. For more information, see Advanced Columnstore Configuration Options. This variable can sync to all aggregators and all leaves.

0.5

columnstore_flush_bytes

Controls the rowstore-backed segment size for columnstore tables. For more information, see Advanced Columnstore Configuration Options. This variable can sync to all aggregators and all leaves.

33554432

columnstore_row_value_table_lock_threshold

Sets the threshold at which multiple inserts to a columstore table with unique keys will switch from row value lock to table lock. This variable can sync to all aggregators and leaves.

1000000 rows

columnstore_segment_rows

Controls the maximum row count for a columnstore segment. For more information, see Advanced Columnstore Configuration Options. This variable can sync to all aggregators and all leaves.

1024000

compiled_images_eviction_memory_limit_mb

Sets a limit in megabytes for the memory amount used for query object code images.

4096

data_conversion_compatibility_level

Specifies the level of data conversion behavior to use. Higher levels throws errors for integer under/overflow, illegal conversion of strings to integers, and string truncation issues. Values can be either '7.5', '7.0', '6.5' or '6.0'. This variable can sync to all aggregators and all leaves. It’s recommended to set this to the highest available level for new application development. For more information, see Data Type Conversion.

'6.0'

deadlock_avoidance_strategy

See deadlock_avoidance_strategy.

wait_die

default_autostats_columnstore_cardinality_mode

Sets the default type of cardinality autostats for newly created columnstore tables. Values can be OFF, INCREMENTAL or PERIODIC. This variable can sync to all aggregators.

INCREMENTAL

default_autostats_columnstore_sampling

Sets the default state for autostats sampling for newly created columnstore tables. This variable can sync to all aggregators.

ON

default_autostats_enabled

Whether autostats is enabled by default on newly created columnstore tables. This variable can sync to all aggregators and all leaves.

ON

default_autostats_histogram_mode

Sets the default type of automatic histograms on newly created tables. This variable can sync to all aggregators. Values can be either OFF, CREATE, or UPDATE.

CREATE

default_autostats_rowstore_cardinality_mode

Sets the default type of cardinality autostats for newly created rowstore tables. Values can be OFF, INCREMENTAL or PERIODIC. This variable can sync to all aggregators.

PERIODIC

default_columnstore_table_lock_threshold

Sets a threshold for the number of rows that are locked before a table lock is acquired when updating or deleting rows in a columnstore table. When set to 0, the threshold of 5000 rows is used. This variable can sync to all aggregators and all leaves. It is a session variable that can be set globally.

0

default_distributed_ddl_timeout

The time, in milliseconds, to wait for a distributed DDL transaction to commit. This value sets the timeout for both ALTER TABLE and BACKUP commands. If the timeout is reached, the transaction is rolled back. This variable can sync to all aggregators and all leaves.

180000

default_partitions_per_leaf

The default number of partitions a newly created database will be created with. When you set this variable, its value is propagated to other aggregators only.

8

default_table_type

The default table type to use when creating a new table. In SingleStore DB, value can be set to columnstore or rowstore. When the value is columnstore you can create a columnstore table using standard CREATE TABLE syntax. In SingleStore Managed Service (SMS), default_table_type is set to columnstore for newly created 7.3 clusters only. For existing SMS clusters, the setting remains at rowstore. This variable is read-only in SMS. This variable can sync to all aggregators.

columnstorein SingleStore DB. In SMS, default_table_type is set to columnstore for newly created 7.3 clusters only. For existing SMS clusters, the setting remains at rowstore.

disable_subquery_merge_with_straight_joins

Whether merging subqueries are disabled if they contain STRAIGHT_JOIN. Here, merging subqueries refers to removing unnecessary nested layers from joins including subqueries. For example, the query select * from (select * from table_a straight_join table_b) table_c straight_join table_d would be rewritten as select * from table_a straight_join table_b straight_join table_d if the engine variable disable_subquery_merge_with_straight_joins is set to OFF. If the variable is set to ON, the query would not be rewritten. The default setting AUTO is equivalent to ON in 7.3. This is a session variable that can also be set globally. This variable can sync to all aggregators and all leaves.

AUTO

disable_update_delete_distributed_transactions

See. Run UPDATEs and DELETEs as Distributed Transactions.

OFF

disk_plan_expiration_minutes

The interval in which a query plan must be read from disk (plancache directory) before it is removed. This variable can sync to all aggregators and all leaves.

20160 (14 days)

distributed_commit_lock_timeout

Deprecated in MemSQL 6.5. Replaced by default_distributed_ddl_timeout.

distributed_heartbeat_timeout

As of MemSQL 6.0, this is the timeout used when gathering workload management statistics from leaves. Before MemSQL 6.0 this was the timeout of the heartbeat query used to trigger failovers. This variable can sync to all aggregators.

10 seconds

distributed_optimizer_max_join_size

This variable is depreciated, but still exists for backward compatibility purposes. As of version 7.3 of SingleStore, it is replaced by two new variables that assist in leveraging significantly increased speed for optimization at large join sizes: distributed_optimizer_unrestricted_search_threshold and singlebox_optimizer_cost_based_threshold. The distributed optimizer works to minimize data movement across the cluster, while the singlebox optimizer makes decisions about how to physically execute a join such as choosing an index. Setting this depreciated variable will result in both new variables being set to the target value.

22

distributed_optimizer_min_join_size_run_initial_heuristics

The minimum number of tables that must be present in a join for initial heuristics to be run before join optimization. This means a small cost is incurred for the initial use of these heuristics in exchange for faster join optimization. This is a session variable that can also be set globally. This variable can sync to all aggregators and all leaves.

16

distributed_optimizer_run_legacy_heuristic

Enabling this variable will result in a return to pre 7.3 behavior through use of heuristics to complete a faster, restricted search for a join plan, once the number of tables in a given join are greater than the threshold set for this with distributed_optimizer_unrestricted_search_threshold. This search is faster, but as the number of tables in a given join increases, the chance of a less optimal query plan also increases. This is a session variable that can also be set globally. This variable can sync to all aggregators and all leaves.

FALSE

distributed_optimizer_unrestricted_search_threshold

The maximum number of tables present in a join that will result in an unrestricted search being performed to find the optimal query plan. A query with a greater number of tables will use heuristics to complete search for a query plan. This restricted search is faster than previous versions of Singlestore. However, this may be at the cost of a less optimal query plan compared to an unrestricted search. distributed_optimizer_run_legacy_heuristic must be set to FALSE in order for this variable to take effect. This is a session variable that can also be set globally. This variable can sync to all aggregators and all leaves.

22

enable_background_plan_invalidation

Controls whether the background statistics thread can invalidate plans automatically. This can improve plans if your data changes over time at the cost of spending time recompiling plans. This variable can sync to all aggregators.

OFF

enable_background_statistics_collection

If set to ON, background statistics are collected for all tables, unless disabled on the table level. If set to OFF, background statistics are not collected for any tables, and background statistics cannot be enabled for individual tables. This variable can sync to all aggregators.

ON

enable_binary_protocol

When this variable is set to ON, server-side prepared statements are enabled. This is a session variable that can also be set globally. This variable can sync to all aggregators and all leaves.

ON

enable_broadcast_left_join

When this variable is set to TRUE, the query optimizer can choose the broadcast left join optimization. This is a session variable that can also be set globally. This variable can sync to all aggregators and all leaves.

TRUE

enable_compiled_images_eviction

Determines whether to use LRU (least recently used) eviction of query object code images.

OFF

enable_disk_plan_expiration

Enable removing of stale on disk plans from the plancache directory based on the value of disk_plan_expiration_minutes. This variable can sync to all aggregators and all leaves.

true

enable_disk_plan_explain

Retains human-readable query plan summaries for compiled query plans. Retained information is available through the SHOW PLAN command. This variable can sync to all aggregators.

OFF

enable_external_functions

See the Enabling External Functions section in Enabling external functions.

OFF

enable_multipartition_queries

When this variable is set to ON, queries are run per leaf instead of per partition on the leaf; the number of threads decreases and performance increases. This is a session variable that can also be set globally. This variable can sync to all aggregators and all leaves.

ON

enable_query_forwarding

Enables the forwarding of DDL queries from a child aggregator to the master. sync_permissions must also be enabled for this variable to take effect; otherwise, an error is returned for DDL queries which are run on a child aggregator. For further information, see Node Requirements for SingleStore DB Commands This variable can sync to all aggregators.

ON

enable_spilling

Enables spilling onto disk for HashGroupBy operations during query processing. When enable_spilling is set to ON, the output of SHOW PROFILE JSON includes the following metrics: spill_outputted_rows : number of rows spilled to disk and spill_disk_usage : number of bytes spilled to disk. The sync variables spilling_node_memory_threshold_ratio and spilling_query_operator_memory_threshold also define the threshold limit to start spilling onto disk.

This variable can sync to all aggregators and all leaves.

OFF

explain_expression_limit

Specifies the maximum number of characters to be used by expressions when outputting the EXPLAIN for a query. This variable can sync to all aggregators and all leaves.

500

explicit_defaults_for_timestamp

Specifies whether the server disables certain nonstandard behaviors for default values and NULL-value handling in TIMESTAMP columns. See Timestamp Behavior for details on this variable. This variable can sync to all aggregators and all leaves.

ON

external_functions_allowlist

See the Enabling External Functions section in Enabling external functions.

failover_initial_grace_interval_seconds

If a node moves offline a second time after just failing and then coming back online failover won’t be triggered again if it happens within grace_interval_seconds. This is avoid a cycle of a problem node failing and coming back online. This variable can sync to all aggregators.

300

geo_sphere_radius

The radius of the sphere used for distance calculation, in meters. (Defaults to average Earth radius.) This variable can sync to all aggregators and all leaves.

6367444.657120

highlight_max_number_fragments

Maximum number of fragments to return from highlight function. This variable can sync to all aggregators and all leaves.

0

highlight_fragment_size

The size of a block of characters used to logically divide up string columns when using the full text search highlight functionality. Minimum value is 10, maximum value is 65535. This variable can sync to all aggregators and all leaves.

100

ignore_insert_into_computed_column

When this variable is set to ON, an INSERT into a computed column succeeds and the INSERT ignores the computed column. When this variable is set to OFF, an INSERT into a computed column fails with an error. This is a session variable that can also be set globally. This variable can sync to all aggregators and all leaves.

OFF

inlist_precision_limit

Specifies the maximum number of list values to consider during histogram estimation for a query with an IN list; a smaller limit will result in a faster compilation time but may also give a less accurate estimate. This is a session variable that can also be set globally. This variable can sync to all aggregators and all leaves.

10000

internal_max_cte_depth

Specifies the maximum number of nested common table expressions (CTEs). For more information, refer to the WITH topic.

128

json_extract_string_collation

Controls the collation setting for JSON_EXTRACT_STRING function. This variable can sync to all aggregators and all leaves. For more details, see the In-Depth Variable Definitions section below.

auto

leaf_failure_detection

Whether or not the master aggregator should detect leaf failures and trigger failovers. WARNING: Turning this variable OFF disables failover. This variable can sync to all aggregators.

On

leaf_failover_fanout

Specifies the placement of replica partitions in a cluster. It can be set to the following modes: paired and load_balanced. For more information, see Managing High Availability.

paired

load_data_errors_retention_minutes

The amount of time, in minutes, that a LOAD DATA error is stored on disk. This variable must be set to at least 0. These errors are surfaced in information_schema.LOAD_DATA_ERRORS as long as they are stored on disk. This variable can sync to all aggregators and all leaves.

1440

load_data_internal_compression

If this variable is set to ON and a network bottleneck is detected, LOAD DATA compresses data on the aggregator before forwarding it to the leaves. This variable can sync to all aggregators and all leaves.

ON

load_data_max_buffer_size

Maximum number of unparsed bytes read by LOAD DATA before throwing an error. This variable can sync to all aggregators and all leaves.

1073741823

load_data_read_size

Number of bytes read at a time by LOAD DATA. This variable can sync to all aggregators and all leaves.

8192

load_data_write_size

Number of bytes written at a time by LOAD DATA. This variable can sync to all aggregators and all leaves.

8192

lock_wait_timeout

Time, in seconds, to wait for a row lock before returning an error. This is a session variable that can also be set globally. This variable can sync to all aggregators and all leaves.

60

log_file_size_partitions

Specifies the log file size (in bytes) for partitions. Can be set to a minimum of 1 MB (in bytes) to maximum of 1 TB (in bytes), in multiples of 1 MB. A MB contains 1048576 bytes. Each partition is pre-allocated two log files. Each of these log files has size log_file_size_partitions. By default, log_file_size_partitions is 256 MB. Changes in the log file size will not affect the sizes of the partitions that are used by existing databases. This variable can sync to all aggregators.

268435456

log_file_size_ref_dbs

Specifies the log file size (in bytes) for reference databases. Can be set to a minimum of 1 MB (in bytes) to maximum of 1 TB (in bytes), in multiples of 1 MB. A MB contains 1048576 bytes. Each reference database is pre-allocated two log files. Each of these log files has size log_file_size_ref_dbs. By default, log_file_size_ref_dbs is 64 MB. Changes in the log file size will not affect existing databases. This variable can sync to all aggregators.

67108864

master_promote_kill_timeout_seconds

Specifies the amount of time online failover will wait to drain open transactions on a master partition (whether running or idle) before killing them.

120

max_async_compilation_concurrency

The number of compiles that can run asynchronously at a given time on each node, when interpreter_mode is set to interpret_first. Its effective value is capped at the number of cores on the host machine. If set to 0, it takes the default value.

Half the number of cores on the host machine.

max_compilation_memory_mb

The maximum amount of memory (in MBs) used to compile a query. An error is returned if the query reaches the specified memory limit.

4096

max_compilation_time_s

The maximum time allowed (in seconds) to compile a query. An error is returned if the query reaches the specified compilation time limit, and any subsequent attempts to compile the query fail.

600

max_connect_errors

If the number of interrupted connections from a host exceeds the value of max_connect_errors this host will be blocked from further connections. This variable can sync to all aggregators and all leaves.

10

multi_insert_tuple_count

Preferred number of tuples in multi-inserts that aggregators send to leaves. This variable can sync to all aggregators and all leaves.

20000

multi_statement_xact_idle_timeout

The time, in seconds, that is allowed for a multi-statement transaction to remain idle while holding locks. This is a session variable that can also be set globally. This variable can sync to all aggregators.

300

optimize_stmt_threshold

A statement count threshold for a procedure or function. When the threshold is exceeded, the procedure or function compiles faster, but the highest level of code optimizations is not applied; however, SQL query optimizations are still in effect. This is a session variable that can also be set globally. This variable can sync to all aggregators and all leaves.

50

optimizer_beam_width

Controls the beam search width. The default value is 10. Setting this to 1 reverts to the previous behavior (prior to v7.5). Higher values (maximum is 1024) will make the one-time query optimization time slower.

10

optimizer_disable_subselect_to_join

Setting this to ON disables the optimizer rewrite that converts subselect to joins automatically.

Disabling this rewrite may cause queries to fail if they require the rewrite to run.

OFF

optimizer_empty_tables_limit

Sets a threshold for the number of empty tables that must be present in a query before the optimizer falls back to being rule based, instead of cost based. This is a session variable that can also be set globally. This variable can sync to all aggregators and all leaves.

0

parametrizer_query_max_params

The maximum number of scalar constants a single query can contain. Any query with more than parametrizer_query_max_params will be failed with an error.

1048576

plan_expiration_minutes

The interval in which a query plan must be reused at least once or it gets unloaded from the query plan cache. This variable can sync to all aggregators and all leaves.

720

preserve_original_colstore_json

A global variable that preserves NULL values and empty arrays in a JSON object that is written to a columnstore table. Set this variable to OFF to disable this setting. For more information on this variable, see the JSON Guide.

AUTO (same as ON)

processlist_rpc_json_max_size

The maximum number of bytes available to the rpc_info column of information_schema.mv_processlist.

2048

redundancy_level

If set to 1, there is no redundancy across leaves. If set to 2, turns on SingleStore DB’s High Availability mode. When you set this variable, its value is propagated to other aggregators only. For more information on this variable, see the Managing High Availability topic. This variable can sync to all aggregators and all leaves.

1

read_advanced_counters

If ON, this variable enables collection of advanced statistics. For more information, see the Advanced Statistics section of the Management View Statistics Reference topic. This variable can sync to all aggregators and all leaves.

OFF

regexp_format

Specifies the regular expression format to be used by regular expression functions that you call. Possible values are 'extended' and 'advanced'. When you set this variable, its value is propagated to all nodes. For more information on this variable, see the Regular Expression Commands topic. This variable can sync to all aggregators and all leaves.

extended

replication_sync

This variable has been deprecated and is no longer operational in SingleStore DB.

resource_governor_cpu_limit_mode

Determines whether the mode of control over the CPU for resource pools is HARD or SOFT. For more information on this variable, see CREATE RESOURCE POOL. This variable can sync to all aggregators and all leaves.

SOFT

resource_pool_statement_selector_function

The function to execute at runtime that selects the resource pool to use when the user runs a query. The resource_pool variable must be set to system_auto for resource_pool_statement_selector_function to be used. For more information on this variable, see the Setting Resource Limits topic. This variable can sync to all aggregators and all leaves.

resource_usage_model

Whether to train or enable the resource usage model for workload management. This variable can sync to all aggregators.

OFF

show_with_portability_comments

Adds conditional compatibility comments to outputs like SHOW CREATE TABLE to help with portability.

FALSE

singlebox_optimizer_cost_based_threshold

The maximum number of tables present in a join which will utilize the cost-based singlebox join optimizer. For joins with more than this many tables, singlebox join optimization will use an alternate, rule-based algorithm which is faster but less effective. The singlebox join optimizer is responsible for making decisions about the local aspects of how to efficiently execute a join, such as choosing an index. This variable must be set between 0 and 30 tables. This is a session variable that can also be set globally. This variable can sync to all aggregators and all leaves.

18

snapshot_trigger_size

The log size (in bytes) which, when reached, will trigger a new snapshot. This variable can sync to all aggregators and all leaves.

2147483648

snapshot_wait_for_blob_gc_seconds

Specifies how much time in seconds to wait between snapshots before taking a snapshot for blob garbage collection from previous snapshots.

180

sp_query_dynamic_param

Specifies whether different query plans are generated for CALL queries when arguments to the stored procedure are NULL or not NULL arguments. If enabled, queries that use variables inside stored procedures will use the same query plan. For more details, see the In-Depth Variable Definitions section below.

ON

spilling_node_memory_threshold_ratio

Memory threshold (ratio of total node memory, 0 - 1) to start spilling.

.75

spilling_query_operator_memory_threshold

Memory threshold (bytes) for a query operator to be considered for spilling.

100000000

sql_select_limit

The maximum number of rows returned by a SELECT query. If the LIMIT clause is specified in a SELECT query, the value in the LIMIT clause overrides sql_select_limit. This is a session variable that can also be set globally. This variable can sync to all aggregators and all leaves.

2^64-1

subprocess_ec2_metadata_timeout_ms

The maximum amount of time, in milliseconds, the engine waits for or retries a request before timing out to return metadata used to verify the cluster is on ec2 from which implicit credentials can be obtained.

1000

subprocess_io_idle_timeout_ms

The maximum amount of time, in milliseconds, the engine waits for or retries a request before timing out and failing the backup when connecting to cloud providers. When you set this variable, its value is propagated to all nodes.

240000

subquery_merge_with_outer_joins

This session variable fine-tunes the behavior of the rewrite SubQueryMerge.

If the variable is set to ON: always merge the sub-select with outer join(s). If the variable is set to HEURISTIC: check to see if merging the sub-select with outer join(s) will cause negative performance for the overall query. If the variable is set to OFF: don’t merge sub-selects with outer join(s). If the variable is set to AUTO (this is the default): For SingleStore 7.5 and previous versions, AUTO will behave like ON. For SingleStore versions after 7.5, AUTO will behave like HEURISTIC.

AUTO

sync_permissions

This aggregator will synchronize its permissions with other aggregators. When ON, this variable also enables DDL forwarding. See Synchronizing Permissions Across Your Cluster for more information about utilizing this variable. This variable can sync to all aggregators.

OFF

sync_slave_timeout

(Deprecated) Maximum amount of time in milliseconds for the master to wait for acknowledgement from the synchronous replica. This variable can sync to all aggregators and all leaves.

10000

syslog_level_NETWORK

Not currently used.

syslog_level_SEND_ERROR

Not currently used.

tracelog_level_NETWORK

Not currently used.

tracelog_level_SEND_ERROR

Not currently used.

wait_die_retry_on_die_sleep_factor

See wait_die_retry_on_die_sleep_factor.

250 milliseconds

Password Complexity Sync Variables

For information about how to configure a password complexity policy, see Configuring a Password Policy.

Name

Description

Default

password_min_length

The minimum number of characters required (0 to 100).

0

password_min_uppercase_chars

The minimum number of uppercase characters required (0 to 100).

0

password_min_lowercase_chars

The minimum number of lowercase characters required (0 to 100).

0

password_min_numeric_chars

The minimum number of numeric digit characters required (0 to 100).

0

password_min_special_chars

The minimum number of special (non-alphanumeric) characters required (0 to 100).

0

password_max_consec_sequential_chars

The maximum number of consecutive characters allowed (0 to 100). For example, if set to 3, passwords with a 4-letter sequence or longer (e.g 1234 or abcd) are disallowed.

0

password_max_consec_repeat_chars

The maximum number of consecutive repeated characters allowed (0 to 100). For example, if set to 3, passwords with 4 or more consecutive repeated characters (e.g., aaaa or 1111) are disallowed.

0

expire_root_password

Specifies whether the root password can expire. If set to ON, the root password will expire after the password_expiration_seconds duration is reached.

OFF

password_expiration_seconds

The time in seconds before a password expires. The value 0 indicates that the password will never expire.

0

password_history_count

The number of previous passwords per user that SingleStore DB will store and disallow from reuse. The value 0 indicates that any previous password can be reused. The maximum is 10.

0

Pipelines Sync Variables

You cannot set a variable for a specific pipeline – each variable setting applies to all pipelines in the cluster.

Name

Description

Default

advanced_hdfs_pipelines

Specifies whether to enable security features for HDFS pipelines. This variable can sync to all aggregators and all leaves.

OFF

ingest_errors_max_disk_space_mb

The maximum amount of disk space, in MB, that is used to log errors for pipelines.

102400

java_pipelines_heap_size

Heap size in megabytes for HDFS pipelines. This variable can sync to all aggregators and all leaves.

8

pipelines_batches_metadata_to_keep

The number of batch metadata entries to persist before they are overwritten by incoming batches. As data is extracted from a source, it’s written in batches to a destination table on a leaf node. Metadata about these batches is temporarily persisted in the master aggregator’s information_schema.PIPELINES_BATCHES table. As new batches are loaded into the database, the oldest batch metadata entries will be removed from the information_schema.PIPELINES_BATCHES table. See the information_schema.PIPELINES_BATCHES Table section for more information about this metadata.

1000

pipelines_deskew_batch_partitions_threshold

For keyless sharded destination tables, if less than this fraction of batch partitions are active, reshuffle to avoid skew. When you set this variable, its value is propagated to all nodes. This variable can sync to all aggregators and all leaves.

0.75

pipelines_errors_retention_minutes

The amount of time, in minutes, that a pipeline error is stored on disk. These errors are surfaced in information_schema.PIPELINES_ERRORS Table as long as they are stored on disk. This variable must be set to at least 0. This variable can sync to all aggregators and all leaves.

1440

pipelines_extractor_debug_logging

Specifies whether to enable extractor debugging for Kafka or HDFS pipelines. This variable currently does not apply to S3 pipelines.

OFF

pipelines_extractor_get_offsets_timeout_ms

The maximum time in milliseconds to wait for offset data to be returned from the data source before returning an error. Increase this value if you experience timeout errors, such as ERROR 1970 (HY000): Subprocess timed out. Use the value 0 to indicate no timeout. This variable can sync to all aggregators and all leaves.

35000

pipelines_extractor_idle_timeout_ms

The maximum time (in milliseconds) that a pipeline will wait for more data from an external source. Use the value 0 to indicate no timeout. This variable can sync to all aggregators and all leaves.

120000

pipelines_kafka_version

The Kafka version used for the Kafka extractor. While the default version is 0.8.2.2, newer versions can also be specified.

0.8.2.2

pipelines_max_concurrent

The maximum number of pipelines running concurrently.

50

pipelines_max_concurrent_batch_partitions

The maximum number of pipeline batch partitions running concurrently.

0

pipelines_max_errors_per_partition

Deprecated in MemSQL 6.7. The maximum number of error event rows per leaf node partition to persist before they are deleted. Once the specified number of rows in the information_schema.PIPELINES_ERRORS table is reached, the database will eventually remove the oldest rows from the table. The removal mechanism for older error data is based on heuristics. Old errors are guaranteed to exist up to the specified number, but they may not immediately be removed.

1000

pipelines_max_offsets_per_batch_partition

The maximum number of data source partition offsets to extract in a single batch transaction. If the data source’s partition contains fewer than the specified number of offsets, all of the partition’s offsets will be batched into the destination table. This variable can sync to all aggregators. This variable applies only to Kafka pipelines.

1000000

pipelines_max_retries_per_batch_partition

The number of retry attempts for writing batch partition data to the destination table. If pipelines_stop_on_error is set to OFF and the specified retry number is reached without success, the batch partition will be skipped and will not appear in the destination table. If a batch partition is skipped, data loss can occur. If pipelines_stop_on_error is set to ON and the specified retry number is reached without success, the pipeline will stop. No batch partition data will be skipped. This configuration variable applies to the entire batch transaction, which includes extraction from a data source, optional transformation, and loading of the data into the destination table. If the batch transaction fails at any point during extraction, transformation, or loading, it will be retried up to the specified number. This variable can sync to all aggregators.

4

pipelines_stderr_bufsize

The buffer size for standard error output in bytes. Error messages that exceed this size will be truncated when written to the information_schema.PIPELINES_ERRORS table. However, the complete standard error text can be viewed by using the BATCH_ID and querying the information_schema.PIPELINES_BATCHES table.

65535

pipelines_stop_on_error

Specifies whether or not each pipeline in the cluster should stop when an error occurs. If set to OFF, batches will be retried up to the number specified in the pipelines_max_retries_per_batch_partition variable. After all retries have failed, the batch will be skipped. When a batch is skipped, data loss can occur. If set to ON, the batch transaction that caused the error will be retried up to the number specified in the pipelines_max_retries_per_batch_partition variable. After all retries have failed, the pipeline will enter a Stopped state and must be manually started. This variable can sync to all aggregators.

ON

pipelines_stored_proc_exactly_once

If set to ON, run stored procedures from pipelines in a transaction. This variable can sync to all aggregators.

ON

Unlimited Storage Database (Bottomless) and Point-in-Time Restore Variables

Name

Description

Default

bottomless_gc_retention_period_minutes

Specifies the amount of time, in minutes, a restore point for a remote storage database is retained after it is created. This determines how far back in time you can do a PITR. For example, to configure retention for 90 days, you should set the value to 90*24*60 = 129600 minutes.

1440

bottomless_snapshot_trigger_log_chunks

Determines how often snapshot files are uploaded to the object store. A higher value will cause snapshot files to be uploaded less frequently. Snapshot files are used during recovery. For example, copying bucket files in an object store to a new location and then running ATTACH at the new location will trigger recovery.

300

bottomless_upload_max_concurrent

A higher value can increase the concurrency of uploading data updates made on the cluster to the object store. A higher value will increase the CPU and memory usage, and potentially the network usage on the cluster.

8

Workload Management Sync Variables

Name

Description

Default

resource_usage_model

Whether to train or enable the resource usage model for workload management. When set to ON, workload management will estimate memory usage and queue queries that are estimated to use too much. When set to TRAINONLY, PROFILE can be run on queries to compare estimated memory usage of queries with their actual use. This is recommended when upgrading from any version prior to 6.7, in order to allow for the workload manager to do the necessary machine learning for accurate estimates. Once estimated memory use in PROFILE begins matching actual use, consider setting this variable to ON. This variable can sync to all aggregators.

OFF

workload_management

Specifies whether to enable workload management for the cluster. If this variable is set to ON, the other workload management engine variables will affect the way a query is executed. If set to OFF, the feature is disabled and no queueing or system resource optimization will occur. This variable can sync to all aggregators.

ON

workload_management_enable_static_partitioning

When set to TRUE, this variable enables static partitioning for deterministic behavior by the Workload Manager, as it was prior to version 7.0. When set to FALSE, partitioning is dynamic, meaning that the Workload Manager allows aggregators to share leaf resources based on each aggregators need. This is an improvement over static partitioning, which could result in wasted resources due to uniform allocation across aggregators. This variable can sync to all aggregators.

FALSE

workload_management_expected_aggregators

The expected number of aggregators that will be used to run a high volume of client queries which require fully distributed execution. The default value is 0, which is equivalent to setting it to the total number of aggregators in the cluster. For version 7.0 and up, this variable should only be set to its default of 0, unless `workload_management_enable_static_partitioning is set to TRUE. This variable can sync to all aggregators.

0

workload_management_max_connections_per_leaf

The maximum number of connections to use per leaf node in the cluster. This variable can sync to all aggregators.

10000

workload_management_max_queue_depth

The maximum depth of the query queue, which is the maximum number of queries that can be queued. If this number is reached, additional queries will not execute, and a ER_TOO_MANY_QUEUED_QUERIES error will appear. This variable can sync to all aggregators.

100

workload_management_max_threads_per_leaf

The maximum number of threads to use per leaf. This number correlates with the max_connection_threads engine variable, and they should generally be set to the same value. This variable can sync to all aggregators.

8192

workload_management_memory_queuing

Whether to turn on queueing based on memory usage of queries. This variable can sync to all aggregators.

ON

workload_management_memory_queue_threshold

Percentage of memory a query can use before it will get queued. If an individual query is projected to use more than workload_management_memory_queue_threshold * (leaf_maximum_memory - leaf_current_table_memory) / workload_management_expected_aggregators, then it will be queued. This variable can sync to all aggregators.

0.01

workload_management_queue_time_warning_ratio

Specifies when a warning will appear based on the ratio of time spent by a query in the queue versus the actual execution time of the query. For example, if a query waits in the queue for one second and it takes four seconds to execute, the ratio is 1:4, or 0.25. Once the specified ratio is reached for a query, a ER_QUERY_QUEUED_WARNING warning will appear. This variable can sync to all aggregators.

0.5

workload_management_queue_timeout

The time duration in seconds after which a query times out and is removed from the queue without being executed. This variable can sync to all aggregators.

3600

Non-Sync Variables List

See the engine variables overview to learn how non-sync variables work.

All of the non-sync variables listed in the following table are global variables, except when noted as a session variable that can also be set globally in the Description column.

The variables listed in the following tables can be set to take effect on node startup and can be set to take effect while the node is running. Exceptions are noted in the fourth column.

Basic Variables

Name

Description

Default Setting

Exceptions to When Variable can be Set

bind_address

If the address is 0.0.0.0, memsql accepts connections on all network interfaces, otherwise it only accepts connections for the given IP address.

0.0.0.0

You can only set this variable while the node is offline. The changes to this variable will take effect on the next start of the node.

div_precision_increment

The number of digits by which to increase the scale of division results performed with the division (/) operator.

4

You can set this variable but it is currently not supported in SingleStore DB. SingleStore DB always returns the results to the fourth precision value.

flush_before_replicate

If ON, data is written and flushed to disk locally before being replicated. This will increase replication latency but will guarantee that replicas will not flush data to disk before the master does.

OFF

You can only set this variable while the node is offline. The changes to this variable will take effect on the next start of the node.

master_aggregator

Appending master_aggregator (with no arguments) to the end of a node’s memsql.cnf specifies that node as the cluster’s master aggregator. For more information on this variable, see Master Aggregator.

You can only set this variable while the node is offline. The changes to this variable will take effect on the next start of the node.

maximum_memory

Maximum memory SingleStore DB will use, in MB. WARNING: Do not set to more than the default.

90% of System RAM or System RAM minus 10 GB, whichever is greater

You are required to restart a node only when the variable is being reduced.

maximum_table_memory

Maximum memory SingleStore DB will use for table storage, in MB. WARNING: Do not set to more than the default.

If maximum_memory >= 10 GB, then 90% of maximum_memory. Else if maximum_memory >= 1.25 GB, then maximum_memory - 1 GB

You are required to restart a node only when the variable is being reduced.

maximum_blob_cache_size_mb

Specifies the maximum blob cache size. The cache stores recently accessed columnstore data objects and is located on the cluster's local storage. The cache exists in  datadir. The cache size is limited by available space in  datadir.

80% of disk space

port

SingleStore DB port number.

3306

You can only set this variable while the node is offline. The changes to this variable will take effect on the next start of the node.

reported_hostname

The hostname or IP of the machine in use.

snapshots_to_keep

Number of snapshots and log files to keep for backup and replication.

2

You can only set this variable while the node is offline. The changes to this variable will take effect on the next start of the node.

datadir

Directory path for the data directory. This directory contains snapshots, logs, and columnstore segments.

You can only set this variable while the node is offline. The changes to this variable will take effect on the next start of the node.

plancachedir

Directory path for the plancache directory. This directory contains compiled plans used for codegen.

./plancache

You can only set this variable while the node is offline. The changes to this variable will take effect on the next start of the node.

tracelogsdir

Directory path for the tracelogs directory. This directory contains log files, including memsql.log and the query log.

./tracelogs

You can only set this variable while the node is offline. The changes to this variable will take effect on the next start of the node.

Connection Management Variables

Name

Description

Default Setting

Exceptions to When Variable can be Set

connect_timeout

The number of seconds the node’s SingleStore DB process is waiting for a connection.

10

max_allowed_packet

Maximum allowed protocol packet size. This is a session variable that can also be set globally.

104857600 bytes

max_connections

The number of simultaneous clients allowed. For more, see In-Depth Variable Definitions.

100000

max_connection_threads

The maximum number of kernel threads for processing queries. For more, see In-Depth Variable Definitions.

192

max_dedicated_admin_connections

Specifies the number of connections reserved for admin users (users granted the SUPER permission). This is the number of connections over and above the max_connections. Its purpose is to allow admin users to login even if max_connections number of non-admin users are already logged in. For example, if max_connections is set to 100 and max_dedicated_admin_connections is set to 5, then even if 100 non admin user connections are active at any time, 5 admin users can still log in. This is to prevent administrative users from being locked out of the system during heavy traffic.

You connect via a socket file, for example: mysql -u root --socket ‘/home/xyz/memsql/bincache/cluster_10000/10000/data/memsql.sock' instead of using mysql -u root -h <host> --port <port>

Refer Dedicated Admin Connections for how to create dedicated admin connections.

5

max_pooled_connections

The maximum number of stashed connections per leaf. For more information on this variable, see In-Depth Variable Definitions.

1024

You can only set this variable while the node is offline. The changes to this variable will take effect on the next start of the node.

skip_name_resolve

Controls whether to perform name resolution. By default, AUTO will only perform a reverse Domain Name System (DNS) lookup if there are any host-based security rules. Options include AUTO, OFF, or ON. For more information on this variable, see In-Depth Variable Definitions.

AUTO

You can only set this variable while the node is offline. The changes to this variable will take effect on the next start of the node.

Database Optimization Variables

Name

Description

Default Setting

Exceptions to When Variable can be Set

columnar_segment_rows

Deprecated alias to columnstore_segment_rows.

1024000

columnstore_window_size

Controls how much columnstore data is kept on disk for replicas to fetch.

2147483648 bytes

max_prepared_stmt_count

The maximum number of simultaneous prepared statements.

16382

net_read_timeout

Number of seconds to wait for more data from a connection before aborting the read. This is a session variable that can also be set globally.

3600

net_write_timeout

Number of seconds to wait for a block to be written to a connection before aborting the write. This is a session variable that can also be set globally.

3600

node_degree_of_parallelism

Controls the number of threads per leaf node for parallel columnstore scans.

0

optimize_columnar_tables

This variable has been deprecated and is no longer operational in SingleStore DB.

query_parallelism

Maximum number of simultaneous running queries. This is a session variable that can also be set globally.

0

transaction_buffer

This variable has been deprecated and is no longer operational in SingleStore DB.

Logging Variables

Name

Description

Default Setting

Exceptions to When Variable can be Set

core_file

Turning core_file on or off determines whether or not full core dumps are produced upon a crash.

ON

critical_diagnostics

Sends usage and critical error diagnostics to SingleStore DB.

ON

general_log

If ON, every query will be logged to a table or log file. If PARTIAL, will log only when load is light. OFF turns off logging.

OFF

general_log_file

Log connections and queries to given file.

/var/lib/memsql/tracelogs/query.log

warn_level

Defines how SingleStore DB behaves when it encounters unsupported functionality. For more information, visit the Unsupported Feature List section of the Unsupported MySQL Features topic.

WARNINGS

Pipelines Variables

You cannot set a variable for a specific pipeline – each variable setting applies to all pipelines in the cluster.

Name

Description

Default Setting

Exceptions to When Variable can be Set

java_pipelines_java_home

Specifies the value that SingleStore DB sets the node’s operating system environment variable JAVA_HOME to. If java_pipelines_java_home is not set, SingleStore DB does not set JAVA_HOME.

You can only set this variable while the node is offline. The changes to this variable will take effect on the next start of the node.

java_pipelines_java_path

Specifies the path that the HDFS extractor uses to run Java.

pipelines_batches_metadata_to_keep

The number of batch metadata entries to persist before they are overwritten by incoming batches. As data is extracted from a source, it’s written in batches to a destination table on a leaf node. Metadata about these batches is temporarily persisted in the master aggregator’s information_schema.PIPELINES_BATCHES table. As new batches are loaded into the database, the oldest batch metadata entries will be removed from the information_schema.PIPELINES_BATCHES table. See information_schema.PIPELINES_BATCHES Table for more information about this metadata.

1000

pipelines_extractor_debug_logging

Specifies whether to enable extractor debugging for Kafka or HDFS pipelines. This variable currently does not apply to S3 pipelines.

OFF

pipelines_kafka_version

The Kafka version used for the Kafka extractor. While the default version is 0.8.2.2, newer versions can also be specified.

0.8.2.2

pipelines_max_concurrent

The maximum number of pipelines running concurrently.

50

pipelines_max_concurrent_batch_partitions

The maximum number of pipeline batch partitions running concurrently.

0

pipelines_max_errors_per_partition

Deprecated in MemSQL 6.7. The maximum number of error event rows per leaf node partition to persist before they are deleted. Once the specified number of rows in the information_schema.PIPELINES_ERRORS table is reached, the database will eventually remove the oldest rows from the table. The removal mechanism for older error data is based on heuristics. Old errors are guaranteed to exist up to the specified number, but they may not immediately be removed.

1000

pipelines_stderr_bufsize

The buffer size for standard error output in bytes. Error messages that exceed this size will be truncated when written to the information_schema.PIPELINES_ERRORS table. However, the complete standard error text can be viewed by using the BATCH_ID and querying the information_schema.PIPELINES_BATCHES table.

65535

Security Variables

Name

Description

Default Setting

Exceptions to When Variable can be Set

ssl_ca

CA file to be used for SSL connections.

You can only set this variable while the node is offline. The changes to this variable will take effect on the next start of the node.

ssl_capath

CA directory to be used for SSL connections.

You can only set this variable while the node is offline. The changes to this variable will take effect on the next start of the node.

ssl_cert

Certificate file to be used for SSL connections.

You can only set this variable while the node is offline. The changes to this variable will take effect on the next start of the node.

ssl_cipher

Cipher to be used for SSL connections.

You can only set this variable while the node is offline. The changes to this variable will take effect on the next start of the node.

ssl_fips_mode

When this variable is set to ON, FIPS mode is enabled.

OFF

You can only set this variable while the node is offline. The changes to this variable will take effect on the next start of the node.

ssl_key

Public-private key pair file to be used for SSL connections.

You can only set this variable while the node is offline. The changes to this variable will take effect on the next start of the node.

ssl_key_passphrase

Passphrase for encrypted ssl_key.

You can only set this variable while the node is offline. The changes to this variable will take effect on the next start of the node.

node_replication_ssl_only

When this variable is set to ON (assuming that SSL is enabled), SSL is used for cross-cluster replication, but not for intra-cluster communication. When the variable is OFF, SSL is used for both cross-cluster as well as intra-cluster replication.

OFF

You can only set this variable while the node is offline. The changes to this variable will take effect on the next start of the node.

Other Variables

Name

Description

Default Setting

Exceptions to When Variable can be Set

activities_delta_sleep_s

activities_delta_sleep_s specifies an interval of time, which is used by the mv_activities_cumulative variable to determine recent resource usage. For more information, see Management View Reference. This is a session variable that can also be set globally.

1 second

auditlogsdir

Specifies the local or network directory to write log files. For more information on this variable, see Configuring Audit Logging.

/<path-to-node-directory>/auditlogs

You can only set this variable while the node is offline. The changes to this variable will take effect on the next start of the node.

auditlog_disk_sync

Specifies if every audit log record is synchronously written and persisted to the disk. By default, it delays the audit log writes to the disk. For more information on this variable, see Configuring Audit Logging.

OFF

You can only set this variable while the node is offline. The changes to this variable will take effect on the next start of the node.

auditlog_level

auditlog_level is used to specify the level of logging in a node. There are 11 logging levels. For more information on this variable, see Audit Logging Levels.

OFF

You can only set this variable while the node is offline. The changes to this variable will take effect on the next start of the node.

auditlog_retention_period

Indicates the retention period (in days) for audit log files.

0 (store files indefinitely)

You can only set this variable while the node is offline. The changes to this variable will take effect on the next start of the node.

auditlog_rotation_size

Specifies the maximum size per log file in bytes. Required if logging is enabled. For more information on this variable, see Configuring Audit Logging.

134217728

You can only set this variable while the node is offline. The changes to this variable will take effect on the next start of the node.

auditlog_rotation_time

Specifies the maximum time duration to write to a single log file in seconds. For more information on this variable, see Configuring Audit Logging.

3600

You can only set this variable while the node is offline. The changes to this variable will take effect on the next start of the node.

auto_replicate

This variable exists for backwards compatibility with MySQL and is non-operational in SingleStore DB.

autocommit

If ON, individual SQL statements are run in a single transaction which commits when the statement finishes. If OFF, individual SQL statements run in a multi-statement transaction by default, which must be ended explicitly with COMMIT or ROLLBACK.

ON

backup_max_threads

Specifies the maximum number of concurrent threads, per leaf, used to run a backup on each leaf. By default, a backup of a leaf uses one thread per partition and there is no restriction on the number of threads created (aside from system limitations).

The number of threads, if set, is shared among active backups, with the first backup using as many as it needs. The remainder, if any, goes to the next backup, etc.

0

basedir

Specifies the path where the installation directory can be found.

You can only set this variable while the node is offline. The changes to this variable will take effect on the next start of the node.

character_set_client

This variable exists for backwards compatibility with MySQL and is non-operational in SingleStore DB.

character_set_connection

This variable exists for backwards compatibility with MySQL and is non-operational in SingleStore DB.

character_set_database

This variable exists for backwards compatibility with MySQL and is non-operational in SingleStore DB.

character_set_filesystem

This variable exists for backwards compatibility with MySQL and is non-operational in SingleStore DB.

character_set_results

This variable exists for backwards compatibility with MySQL and is non-operational in SingleStore DB.

character_set_system

The character set used to store identifiers. The value is read-only and always has the value utf8.

utf8

character_sets_dir

Specifies the directory where character sets are stored.

/var/lib/memsql/share/charsets/

You can only set this variable while the node is offline. The changes to this variable will take effect on the next start of the node.

compile_only

If ON, SingleStore DB will compile, but not run, each query it receives. This is a session variable that can also be set globally.

OFF

You cannot set this variable while the node is offline.

convert_nonunique_hash_to_skiplist

When this variable is set as TRUE, any non-unique hash index will be recovered as a skiplist index. Any newly created table will also have its non-unique hash indexes created as skiplists.

TRUE

You can only set this variable while the node is offline. The changes to this variable will take effect on the next start of the node.

core_file_mode

Specifies type of core dump to generate if SingleStore DB terminates abnormally. Options include NONE, PARTIAL, or FULL. PARTIAL omits most user data to keep the dump small, while a FULL core dump uses the equivalent amount of disk space as the amount of memory used by SingleStore DB.

PARTIAL

You can only set this variable while the node is offline. The changes to this variable will take effect on the next start of the node.

date_format

This variable exists for backwards compatibility with MySQL and is non-operational in SingleStore DB.

%Y-%m-%d

datetime_format

This variable exists for backwards compatibility with MySQL and is non-operational in SingleStore DB.

%Y-%m-%d %H:%i:%s

default_time_zone

This is a configuration variable that is used to set the time zone on a host by specifying an offset from UTC time. Refer to Setting the Time Zone for details on this variable.

enable_dml_query_forwarding

When set to ON, forwards the Data Manipulation Language (DML) queries from a child aggregator to the master aggregator. Currently, this setting is used for write requests to reference tables, which cannot be executed on child aggregators.

ON

error_count

This variable exists for backwards compatibility with MySQL and is non-operational in SingleStore DB.

0

external_user

This variable exists for backwards compatibility with MySQL and is non-operational in SingleStore DB.

flat_plancache

This variable has been deprecated and is no longer operational in SingleStore DB version 5.0 or newer.

group_concat_max_len

This variable is the maximum length string GROUP_CONCAT() can return in bytes. It is a session variable which can be set globally and can be set to any value smaller than or equal to max_allowed_packet. For more information on this variable see max_allowed_packet in the previous section and the GROUP_CONCAT SQL reference. This variable should be updated on all nodes and requires a restart to pick up the new value.

16777216

You can only set this variable while the node is offline. The changes to this variable will take effect on the next start of the node.

gssapi_keytab_path

The local path to the keytab file created on the KDC. For more information on this variable, see Kerberos Authentication.

You can only set this variable while the node is offline. The changes to this variable will take effect on the next start of the node.

gssapi_principal_name

The SPN for SingleStore DB that was created on the KDC. For more information on this variable, see Kerberos Authentication.

You can only set this variable while the node is offline. The changes to this variable will take effect on the next start of the node.

hostname

The server host name specified by the server at startup. This variable is read-only.

http_api

Enables SingleStore's HTTP API endpoints on the built-in HTTP server when used in conjunction with the https_proxy_port or the http_proxy_port variable. This variable must be set locally on each aggregator node on which the HTTP API need to be run.

OFF

http_api_pool_capacity

Specifies the maximum number of connections each pool can have open at any point in time when using SingleStore's HTTP APIs. In other words, this variable controls the number of parallel queries that can be run by a SingleStore user.

0

http_api_pool_max_idle

Specifies the maximum number of idle connections to retain in each connection pool when using SingleStore's HTTP APIs. Each connection pool is associated with a single SingleStore user.

16

http_proxy_port

Specifies the port on which the WebSocket proxy should run. This WebSocket allows SingleStore DB Studio to connect with the SingleStore DB server over HTTP using TLS (Learn more).

The http_proxy_port variable when used in conjunction with the http_api variable provides access to SingleStore's HTTP APIs via the HTTP server (Learn more). 

Note: This variable is mutually exclusive with the https_proxy_port variable.

https_proxy_port

Specifies the port on which WebSocket proxy should run. This WebSocket allows SingleStore DB Studio to connect with the SingleStore DB server over HTTPS using TLS. It requires SSL to be enabled (Learn more).

The https_proxy_port variable when used in conjunction with the http_api variable provides access to SingleStore's HTTP APIs via the HTTPS server (Learn more). 

Note: This variable is mutually exclusive with the http_proxy_port variable.

idle_thread_lifetime_seconds

Idle threads terminate after the specified number of seconds.

3600

identity

Contains the value of last_insert_id. This is a session variable that can also be set globally.

You cannot set this variable while the node is offline.

interactive_timeout

This variable exists for backwards compatibility with MySQL and is non-operational in SingleStore DB.

28800 seconds

internal_columnstore_validate_blob_after_write

If set to ON, the checksum of a blob is verified immediately after it is created.

OFF

internal_columnstore_validate_blob_before_read

If set to ON, the checksum of a blob is verified before it is read.

OFF

interpreter_mode

Controls whether SingleStore compiles or interprets query plans. When compiling, this variable also controls how the query plans are compiled. Allowed settings include: llvm, mbc, compile, compile_lite, compile_lite_first, interpret, interpret_first. See Code Generation for more details. This is a session variable that can also be set globally.

interpret_first

json_agg_max_len

Controls the maximum length of JSON_AGG output. It can be set to a minimum of 1 MB (in bytes). This is a session variable that can also be set globally.

16777216 Bytes

kerberos_server_keytab

This variable has been deprecated and is no longer operational in SingleStore DB.

lc_messages

This variable exists for backwards compatibility with MySQL and is non-operational in SingleStore DB.

lc_messages_dir

Specifies the directory where error messages are stored.

/var/lib/memsql/share/

You can only set this variable while the node is offline. The changes to this variable will take effect on the next start of the node.

lc_time_names

This variable exists for backwards compatibility with MySQL and is non-operational in SingleStore DB.

en_US

load_data_batch_size

This variable has been deprecated and is no longer operational in SingleStore DB version 5.0 or newer.

local_infile

This variable exists for backwards compatibility with MySQL and is non-operational in SingleStore DB.

ON

locked_in_memory

This variable exists for backwards compatibility with MySQL and is non-operational in SingleStore DB.

OFF

materialize_ctes

Specifies the setting to materialize the common table expressions (CTEs). If set to OFF, it inlines the CTEs similar to view definitions. If set to ALL, then each CTE appearing more than once in a query is materialized into an internal result table. If set to AUTO, optimizations are enabled. Currently, only the predicate pushdown optimization is available. This engine variable is experimental and should not be enabled in production. For more information, see Materializing Common Table Expressions.

OFF

max_user_connections

This variable exists for backwards compatibility with MySQL and is non-operational in SingleStore DB.

memsql_id

The ID of the SingleStore DB node whose config you would like to update. This variable is read-only.

memsql_version

SingleStore DB version number. This variable is read-only.

memsql_version_date

The build date of the SingleStore DB version currently running. This variable is read-only.

memsql_version_hash

SingleStore DB version hash. This variable is read-only.

minimal_disk_space

Sets the minimal available disk space allowed (in MBs). If the available disk space falls below minimal_disk_space on the disk where the data directories (such as logs, snapshots, blobs, plancache, and tracelogs) are mounted, SingleStore DB will halt new write queries.

100 MB

net_buffer_length

Specifies the size of the connection buffer and the result buffer with which each client thread starts. This is a session variable that can also be set globally.

102400 bytes

net_retry_count

This variable exists for backwards compatibility with MySQL and is non-operational in SingleStore DB.

10

pid_file

The path name of the process ID file.

/var/lib/memsql/memsql.pid

You can only set this variable while the node is offline. The changes to this variable will take effect on the next start of the node.

profile_for_debug

This variable enables collection of additional data with PROFILE that can be displayed using SHOW PROFILE JSON and is useful for troubleshooting query optimizer issues. For more information, see PROFILE. This is a session variable that can also be set globally.

OFF

protocol_version

Specifies the version of the client/server protocol. This variable is read-only.

10

proxy_user

This variable exists for backwards compatibility with MySQL and is non-operational in SingleStore DB.

ref_repl_mgmt_threads

The number of threads pooled for replication management of reference databases. Must be between 1 and 100.

8

repl_mgmt_threads

The number of threads pooled for replication management of partition databases. Must be between 1 and 100.

8

resource_pool

Specifies the resource pool to be used. This is a session variable that can also be set globally. It can be set while a node is running, but cannot be set on node startup. For more information on this variable, see Setting Resource Limits.

default_pool

rewrite_verbose

This variable determines verbose debug tracing for rewrites. OFF: no output. ON: query before and after each rewrite; some extra tracing inside some rewrites.

OFF

saml_assertion_audience

Specifies a single audience restriction for the SAML assertion. For more information on this variable, see Configuring SAML Global Variables.

You can only set this variable while the node is offline. The changes to this variable will take effect on the next start of the node.

saml_message_recipient

Specifies the intended recipient for a wrapped encryption key. For more information on this variable, see Configuring SAML Global Variables.

You can only set this variable while the node is offline. The changes to this variable will take effect on the next start of the node.

saml_private_decryption_key

Specifies the file path for the private key used to decrypt an encrypted assertion. For more information on this variable, see Configuring SAML Global Variables.

You can only set this variable while the node is offline. The changes to this variable will take effect on the next start of the node.

saml_require_encryption

Specifies if authentication should fail when both the SAML response and SAML assertion are unencrypted. For more information on this variable, see Configuring SAML Global Variables.

OFF

You can only set this variable while the node is offline. The changes to this variable will take effect on the next start of the node.

saml_require_signature_validation

Specifies if authentication should fail when both the SAML response an SAML assertion are unsigned. For more information on this variable, see Configuring SAML Global Variables.

OFF

You can only set this variable while the node is offline. The changes to this variable will take effect on the next start of the node.

saml_use_NameID

Specifies whether a username value should be extracted from the <saml:NameID> element in a SAML assertion. For more information on this variable, see Configuring SAML Global Variables.

OFF

You can only set this variable while the node is offline. The changes to this variable will take effect on the next start of the node.

saml_user_name_attribute

Specifies the username attribute in a SAML assertion that should be used to determine if a user exists in the database. For more information on this variable, see Configuring SAML Global Variables.

You can only set this variable while the node is offline. The changes to this variable will take effect on the next start of the node.

saml_x509_certificate

Specifies the file path for the identity provider’s public x509 signing certificate. For more information on this variable, see Configuring SAML Global Variables.

You can only set this variable while the node is offline. The changes to this variable will take effect on the next start of the node.

secure_file_priv

Specifies the directory to which any import or export operations should be limited, or disables import and export entirely if set to NULL.

You can only set this variable while the node is offline. The changes to this variable will take effect on the next start of the node.

show_query_parameters

If ON, query parameters will be visible in the output of SHOW PROCESSLIST and in the output of SELECT from INFORMATION_SCHEMA.PROCESSLIST. If it is OFF, parameters will be hidden.

ON

You can only set this variable while the node is offline. The changes to this variable will take effect on the next start of the node.

socket

Specifies the Unix socket file to use for local connections.

memsql.sock

You can only set this variable while the node is offline. The changes to this variable will take effect on the next start of the node.

sql_mode

Specifies the SQL mode or modes that affect the SQL syntax SingleStore DB supports and the query validation checks it performs. This is a session variable that can also be set globally. See the sql_mode section below for more information.

STRICT_ALL_TABLES

sql_quote_show_create

If ON, identifiers are quoted by the server for SHOW CREATE commands. This is a session variable that can also be set globally.

ON

system_time_zone

System time zone. This variable is read-only.

PST

table_name_case_sensitivity

Sets the case-sensitivity for database object names. If set to OFF, tables, views, table aliases, and user-defined table-valued functions (TVFs) are not case-sensitive. For details on case-sensitivity, refer to Database Object Case-Sensitivity. This variable can sync to all aggregators and all leaves.

ON

table_precompiled_header

This variable has been deprecated and is no longer operational in SingleStore DB version 5.0 or newer.

thread_cache_size

Specifies how many inactive connection threads should be cached.

0

thread_handling

Determines how the server handles connection threads. A value of no-threads will cause the server to use a single thread to handle one connection. one-thread-per-connection causes the server to use one thread for each client connection.

one-thread-per-connection

You can only set this variable while the node is offline. The changes to this variable will take effect on the next start of the node.

thread_stack

Specifies the stack size for each thread.

1048576 bytes

You can only set this variable while the node is offline. The changes to this variable will take effect on the next start of the node.

time_format

This variable exists for backwards compatibility with MySQL and is non-operational in SingleStore DB.

%H:%i:%s

time_zone

The current time zone. By default, it is set to the same value as that of system_time_zone. This is a session variable that can also be set globally, but it is a noop, for MySQL compatibility. Change the time zone using your OS (preferred) or the Setting the Time Zone config variable.

SYSTEM

timestamp

Used to capture the original timestamp of the client. This is a session variable that can also be set globally. It can be set while a node is running, but cannot be set on node startup.

1391112305 seconds

tls_version

Indicates the TLS version with which to configure the node. For more information, see Specifying the TLS Version

You can only set this variable while the node is offline. The changes to this variable will take effect on the next start of the node.

tmpdir

MemSQL Ops writes temporary data to /tmp and requires available free space. It is possible to change the temporary directory by changing tmpdir.

You can only set this variable while the node is offline. The changes to this variable will take effect on the next start of the node.

transaction_read_only

This variable exists for backwards compatibility with MySQL and is non-operational in SingleStore.

tx_isolation

Transaction isolation level. This is a session variable that can also be set globally.

READ-COMMITTED

tx_read_only

This variable exists for backwards compatibility with MySQL and is non-operational in SingleStore.

use_vectorized_join

This variable has been deprecated and is no longer operational in SingleStore DB version 5.0 or newer.

version

This variable exists for backwards compatibility with MySQL and is non-operational in SingleStore DB. To check the version of SingleStore DB you are running, use the memsql_version variable instead.

version_comment

This variable exists for backwards compatibility with MySQL and is non-operational in SingleStore DB.

version_compile_machine

The type of the server binary. This variable is read-only.

x86_64

version_compile_os

The operating system on which SingleStore DB was built. This variable is read-only.

Linux

wait_timeout

This variable exists for backwards compatibility with MySQL and is non-operational in SingleStore DB.

28800 seconds

warning_count

This variable exists for backwards compatibility with MySQL and is non-operational in SingleStore DB.

0

In-Depth Variable Definitions

This section contains supplemental information about engine variables that require more understanding to configure properly. Ensure that you understand these details before modifying any engine variables listed in this section.

max_connection_threads

max_connection_threads is the maximum number of kernel-level threads the SingleStore DB node will use to handle connections (i.e. running queries - not including background threads). Each query takes exactly one thread on the aggregator, so the max_connection_threads setting on an aggregator is essentially a limit on the number of queries - including internal SingleStore DB queries - the aggregator will run simultaneously. When the limit is reached, further queries are queued until a thread becomes available.

The maximum value of max_connection_threads is 8192. The default for aggregators is 192, and the default for leaves is 8192. Since leaves are defaulted to the highest setting, there is typically no reason to change this variable for leaves.

If the max_connection_threads limit is reached on an aggregator, queries are queued until a thread becomes available, which can potentially cause unresponsiveness, latency spikes, and failures. On the other hand, in rarer cases, too many queries running simultaneously on some workloads (such as high volume concurrent writes on larger clusters) can exhaust cluster resources. Typically, if the max_connection_threads limit is reached on an aggregator, increasing the limit should solve the problem. If raising the limit causes further problems on your workload, you may need to explore other avenues to resolve the root cause.

max_pooled_connections

max_pooled_connections is the maximum number of connections cached between nodes. Every connection that is opened to run a query between nodes will be left open and reused until the limit set by max_pooled_connections is reached. If more connections are needed to run a workload, the connections will be opened/closed as needed as the query runs. This is why running SHOW PROCESSLIST on a leaf that has been running a workload will show both open and idle connections.

The default value is 1024, which is typically sufficient. Some heavy distributed join workloads may need more internode connections, in which case this variable can be changed.

max_connections

max_connections is the maximum number of connections that can be open to a SingleStore DB node at one time. The default is 100,000, which is the maximum allowed. There is no reason to change the value of max_connections as lowering its value would not impact resource allocation.

node_degree_of_parallelism

Sets the per-node degree of parallelism for applicable query operators. If the variable is set to 0 the parallelism is chosen automatically (i.e. no change from default behavior).

When node_degree_of_parallelism is set to a value other than 0, say n, then n processor threads are started on each leaf node to handle all the partitions on that leaf.

interpreter_mode

Controls both whether and how SingleStore DB compiles or interprets query plans. Allowed settings include the following modes:

  • llvm or compile: Queries are compiled to machine code. compile is an alias for llvm.

  • mbc or interpret : Queries are interpreted and not compiled. interpret is an alias for mbc.

  • interpret_first: Queries start out as interpreted and dynamically switch to compiled during the first query execution. This mode can help improve ad-hoc query performance. The interpret_first mode is turned on by default and can be used in production deployments.

This variable can also be set as a query option by adding OPTION (interpreter_mode = { interpret | compile | interpret_first}) at the end of the query. interpreter_mode is non-operational on the leaf node since it is forwarded from the aggregator to the leaf.

For more information on interpreter_mode and query compilation behavior, see Code Generation.

sp_query_dynamic_param
Syntax
SET GLOBAL sp_query_dynamic_param = {ON | OFF};
Remarks

When set to ON, sp_query_dynamic_param changes the plan generation behavior as follows:

  • Calls to a stored procedure use the same plan, regardless of whether the arguments to the procedure are NULL or not NULL. For example, the following procedure calls use the same plan:

    CALL proc_test(1, NULL, 7);
    CALL proc_test("Adam", NULL, 4);
    CALL proc_test(NULL, "Sam", "Smith");
    

    The following procedure calls use different query plans, because of different number of arguments:

    CALL proc_test(NULL);
    CALL proc_test(NULL, 7);
    
  • All occurrences of a query, inside a stored procedure, that uses variables will use the same plan, regardless of whether the variable values are NULL or not NULL. This applies when such a query appears in the stored procedure multiple times or when the query runs repeatedly via multiple calls to the stored procedure.

When sp_query_dynamic_param is enabled, compilation time and plancache size are reduced.

Notice

The OFF setting of sp_query_dynamic_param disables the plan generation behavior described above. This setting will no longer be supported around May 2021. You should remove any dependencies on the setting by this time.

Example: Changes in Type Conversion Behavior

A query returns different results for cases where an invalid conversion is being done, depending on the value of sp_query_dynamic_param. For example, in the query below, 9006060 is an invalid value for TIME datatype.

If sp_query_dynamic_param is disabled,

DELIMITER //

CREATE OR REPLACE PROCEDURE sp_ex (t TIME) AS
BEGIN
  ECHO SELECT t AS "t";
END; //

DELIMITER ;

CALL sp_ex(9006060);
****
+-----------+
| t         |
+-----------+
| 838:59:59 |
+-----------+

If sp_query_dynamic_param is enabled,

DELIMITER //

CREATE OR REPLACE PROCEDURE sp_ex (t TIME) AS
BEGIN
  ECHO SELECT t AS "t";
END; //

DELIMITER ;

CALL sp_ex(9006060);
****
+----------+
| t        |
+----------+
| 00:00:00 |
+----------+
json_extract_string_collation

json_extract_string_collation allows you to control the collation of JSON_EXTRACT_STRING output. It takes the following values:

  • json: Specifies that the result of JSON_EXTRACT_STRING will use the standard collation used for JSON (binary), which is utf8_bin.

  • server: Specifies that the collation of JSON_EXTRACT_STRING result will be the same as collation of the server defined by the collation_server variable. Generally, this value is utf8_general_ci.

  • auto: Interpreted as the server setting for json_extract_string_collation.

skip_name_resolve

skip_name_resolve controls whether the server performs name resolution via DNS lookup upon login. The possible values for this variable are:

  • AUTO: By default, AUTO will only perform a reverse DNS lookup if there are any host-based security rules.

  • OFF: Always uses name resolution. This is not recommended without a reliable existing DNS.

  • ON: Disables DNS and never uses name resolution. The server matches only IP addresses (not host names) to the list of grants. This can improve performance for users with a slow DNS and many hosts.

sql_mode

sql_mode specifies the current SQL mode (or modes) that the current session runs in. Currently, SingleStore DB supports the following SQL modes:

  • ANSI_QUOTES: Changes " to be treated as the identifier quote character (like the ` quote character) and not as a string quote character. You can still use ` as an identifier quote character with this mode enabled. With ANSI_QUOTES enabled, you cannot use double quotation marks to quote literal strings because they are interpreted as identifiers.

  • ANSI: Sets sql_mode to STRICT_ALL_TABLES, ONLY_FULL_GROUP_BY, PIPES_AS_CONCAT, and ANSI_QUOTES together.

  • NO_AUTO_CREATE_USER: Throws an error when using GRANT on non-existent users. Default behavior is to create a user instead.

  • ONLY_FULL_GROUP_BY: Throws an error when fields in the SELECT list, HAVING condition, or ORDER BY list are not in a GROUP BY clause, or are outside of an aggregate function. This is because the result set could include multiple possible values for the non-grouped, non-aggregated field.

  • PIPES_AS_CONCAT: Changes || to be treated as string concatenation operation and not as an OR operation. You can still use built-in function CONCAT as a string concatenation with this mode enabled.

  • STRICT_ALL_TABLES: Always enabled, regardless of other modes being enabled or not. If set to an empty value, behavior is the same as if STRICT_ALL_TABLES is set.

ssl_key_passphrase

The passphrase specified with ssl_key_passphrase is used to decrypt the encrypted Privacy Enhanced Mail (PEM) or Password Protected (PASS) file. It can be added for encrypted SSL either at runtime or in memsql.cnf file and can used for both intra-cluster and inter-cluster configuration. The PEM or PASS file is decrypted once at boot time.

Example

The following examples show how to set sql_mode with one more or more values.

SELECT @@sql_mode;
+-------------------+
| @@sql_mode        |
+-------------------+
| STRICT_ALL_TABLES |
+-------------------+
1 row in set (0.00 sec)

-- Set sql_mode to include ONLY_FULL_GROUP_BY

SET sql_mode = 'ONLY_FULL_GROUP_BY';
Query OK, 0 rows affected (0.00 sec)

SELECT @@sql_mode;
+--------------------------------------+
| @@sql_mode                           |
+--------------------------------------+
| ONLY_FULL_GROUP_BY,STRICT_ALL_TABLES |
+--------------------------------------+
1 row in set (0.01 sec)

-- Set sql_mode to ANSI_QUOTES, which replaces ONLY_FULL_GROUP_BY

SET sql_mode = 'ANSI_QUOTES';
Query OK, 0 rows affected (0.00 sec)

SELECT @@sql_mode;
+-------------------------------+
| @@sql_mode                    |
+-------------------------------+
| ANSI_QUOTES,STRICT_ALL_TABLES |
+-------------------------------+
1 row in set (0.00 sec)

-- Set ONLY_FULL_GROUP_BY and ANSI_QUOTES together

SET sql_mode = 'ONLY_FULL_GROUP_BY,ANSI_QUOTES';
Query OK, 0 rows affected (0.01 sec)

SELECT @@sql_mode;
+--------------------------------------------------+
| @@sql_mode                                       |
+--------------------------------------------------+
| ANSI_QUOTES,ONLY_FULL_GROUP_BY,STRICT_ALL_TABLES |
+--------------------------------------------------+
1 row in set (0.01 sec)