Load Data from MongoDB®

Replicate MongoDB® Collections using SQL

To replicate your existing MongoDB® collections to your SingleStore database using SQL syntax for pipelines, create a link to the MongoDB® endpoint using the CREATE LINK statement, and use one of the following methods:

To replicate/migrate collections (as is), use the CREATE {TABLES | TABLE} AS INFER PIPELINE ... SQL statement. Refer to Remarks for more information.
To apply transformations and manually ingest the collections,
1. Create a table with a structure that can store the ingested collections.
2. Create a stored procedure to map the MongoDB® collection to the SingleStore table and implement other transformations required.
3. Create a pipeline to ingest the MongoDB® collections using the CREATE AGGREGATOR PIPELINE SQL statement. Refer to Parameters for a list of supported parameters.
  
  Note
  
  The CDC feature only supports AGGREGATOR pipelines.
(Optional) Run the CREATE {TABLES | TABLE} AS INFER PIPELINE ... SQL statement to infer the schema of the collection(s) and generate the relevant table(s), stored procedure, and aggregator pipeline, automatically. Subsequently, use the automatically generated stored procedure and pipeline as a base for custom transformations. To inspect the stored procedure and pipeline, use the SHOW CREATE PROCEDURE and SHOW CREATE PIPELINE commands, respectively.

Once all the components are configured, start the pipelines.

Syntax

SQL

CREATE LINK [db_name.]connection_name AS MONGODB
CREDENTIALS 'credentials_json' [<link_configuration>]

Refer to CREATE LINK for the complete syntax and related information.

SQL

CREATE TABLE <table_name> AS INFER PIPELINE AS LOAD DATA 
[ LINK <link_name> FORMAT AVRO ... ] 
[ MONGODB <collection> CONFIG <conf_json> CREDENTIALS <cred_json> FORMAT AVRO ... ]

CREATE TABLES AS INFER PIPELINE AS LOAD DATA 
[ LINK <link_name> FORMAT AVRO ... ]
[ MONGODB '*' CONFIG <conf_json> CREDENTIALS <cred_json> FORMAT AVRO ... ]

Refer to CREATE TABLE for related information.

SQL

CREATE [OR REPLACE] AGGREGATOR PIPELINE [IF NOT EXISTS] <pipeline_name> AS 
LOAD DATA MONGODB <link_configuration> ...
<avro_format_options>

<link_configuration>:
   LINK [<database_name>.]<connection_name> '<path>'

<avro_format_options>:
    FORMAT AVRO SCHEMA REGISTRY {uri}
    ( {<column_name> | @<variable_name>} <- <subvalue_path>, ...)
    [SCHEMA '<avro_schema>']
    [KAFKA KEY ( {<column_name> | @<variable_name>} <- <subvalue_path>, ...)]

Refer to CREATE PIPELINE for the complete syntax and related information.

Refer to CREATE PROCEDURE for information on creating stored procedures.

Parameters

The CREATE AGGREGATOR PIPELINE ... AS LOAD DATA MONGODB statement supports the following parameters in the CONFIG/CREDENTIALS clause:

mongodb.hosts: A comma-separated list of MongoDB® servers (nodes) in the replica set, in 'hostname:[port]' format.
- If mongodb.members.auto.discover is set to FALSE, you must prefix the 'hostname:[port]' with the name of the replica set in mongodb.hosts, e.g., rset0/svchost-xxx:27017. The first node specified in mongodb.hosts is always selected as the primary node.
- If mongodb.members.auto.discover is set to TRUE, you must specify both the primary and secondary nodes in the replica set in mongodb.hosts.
mongodb.members.auto.discover: Specifies whether the MongoDB® servers defined in mongodb.hosts should be used to discover all the members of the replica set. If disabled, the servers are used as is.
mongodb.user: The name of the database user to use when connecting to MongoDB® servers.
mongodb.password: The password to use when connecting to MongoDB® servers.
mongodb.ssl.enabled: Enables the connector to use SSL when connecting to MongoDB® servers.
mongodb.authsource: Specifies the database containing MongoDB® credentials to use as an authentication source. This parameter is only required when the MongoDB® instance is configured to use authentication with an authentication database other than admin.
collection.include.list: A comma-separated list of regular expressions that match fully-qualified namespaces (in databaseName.collectionName format) for MongoDB® collections to monitor. Collections excluded from the list are not monitored. By default, all collections are monitored, except for those in the local and admin databases. The list must contain the singlestore.signals collection, in addition to the specified regular expressions. Also, the MongoDB® user must have write permissions to the singlestore.signals collection.
signal.data.collection (Optional): A collection in the remote source that is used by SingleStore to generate special markings for snapshotting and synchronization. By default, this parameter is set to singlestore.signals. The default signal collection is in the database named singlestore. The MongoDB® user must have write permissions to this collection.
max.queue.size: Specifies the size of the queue inside the extractor process for records that are ready for ingestion. The default queue size is 1024. This variable also specifies the number of rows for each partition. Increasing the queue size results in an increase in the memory consumption by the replication process and you may need to increase the pipelines_cdc_java_heap_size.
max.batch.size: Specifies the maximum number of rows of data fetched from the remote source in a single iteration (batch). The default batch size is 512. max.batch.size must be lower than max.queue.size.
poll.interval.ms: Specifies the interval for polling of remote sources if there were no new records in the previous iteration in the replication process. The default interval is 500 milliseconds.
snapshot.mode: Specifies the snapshot mode for the pipeline. It can have one of the following values:
- "initial" (Default): Perform a full snapshot first and replay CDC events created during the snapshot. Then, continue ingestion using CDC.
- "incremental": Start the snapshot operation and CDC simultaneously.
- "never": Skip the snapshot, and ingest changes using CDC.
Refer to CDC Snapshot Strategies for more information.

Remarks

The CREATE TABLE <table_name> AS INFER PIPELINE statement,
1. Connects to the MongoDB® servers using the specified LINK <link_name> or MONGODB <collection> CONFIG <conf_json> CREDENTIALS <cred_json> clause.
2. Discovers the available databases and collections filtered by collection.include.list.
3. Infers the schema of the collection and then creates a table (named <table_name>) in SingleStore using the inferred schema. You can also specify a table name that differs from the name of the source MongoDB® collection.
4. Creates a pipeline (named <table_name>) and stored procedure (named <table_name>_apply_changes) that maps the AVRO data structure to the SingleStore data structure.
The CREATE TABLES AS INFER PIPELINE statement creates a table for each collection in the source database using the same set of operations as the CREATE TABLE <table_name> AS INFER PIPELINE statement (specified in the previous list item).
The MONGODB source only supports AVRO data type.
Use the SYNC PIPELINE <pipeline_name> statement to replicate (sync with) the data source.

Source Database Requirements

The replication feature uses MongoDB® change streams, and it works only with replica sets. A MongoDB® user must have the following roles (privileges) to replicate the collections in SingleStore:

Read the admin database for the operation log (oplog)
Read the config database in the configuration server
listDatabases privilege
Cluster-wide find and changeStream privileges

CDC Snapshot Strategies

SingleStore supports the following strategies for creating snapshots:

Perform a full snapshot before CDC: The pipeline captures the position in the oplog and then performs a full snapshot of the data. Once the snapshot is complete, the pipeline continues ingestion using CDC. This strategy is enabled by default.

To use this strategy, set "snapshot.mode":"initial" in the CONFIG JSON.

Requirement: The oplog retention period must be long enough to maintain the records while the snapshot is in progress. Otherwise, the pipeline will fail and the process will have to be started over.
CDC only: The pipeline will not ingest existing data, and only the changes are captured using CDC.

To use this strategy, set "snapshot.mode":"never" in the CONFIG JSON.
Perform a snapshot in parallel to CDC: The pipeline captures the position in the oplog and starts capturing the changes using CDC. In parallel, the pipeline performs incremental snapshots of the existing data and merges it with the CDC records.

To use this strategy, set "snapshot.mode":"incremental" in the CONFIG JSON.

Requirement: The oplog retention period must be long enough to compensate for unexpected pipeline downtime.
Manually perform the snapshot and capture changes using the CDC pipeline:
1. Create a pipeline and then wait for at least one batch of ingestion to capture the oplog position.
2. Stop the pipeline.
3. Snapshot the data using any of the suitable methods, for example, mongodump and mongorestore.
4. Start the pipeline.
To use this strategy, set "snapshot.mode":"never" in the CONFIG JSON.

Requirement: The oplog retention period must be long enough to maintain the records while the snapshot is in progress. Otherwise, the pipeline will fail and the process will have to be started over.

Configure Ingestion Speed Limit

Use the pipelines_cdc_row_emit_delay_us engine variable to limit the impact of CDC pipelines on the master aggregator node. It specifies a forced delay in row emission during ingest. This variable can be set to a maximum value of 1000000. To disable the forced delay while ingestion, set this variable to 0.

Warning

Disabling the emit delay may result in excessive CPU usage on master aggregator nodes.

Use the max.queue.size parameter in the CONFIG JSON to control the ingestion speed. SingleStore recommends setting max.batch.size to half of max.queue.size. Increasing the queue size requires a larger Java heap limit, adjust the pipelines_cdc_java_heap_size engine variable accordingly. Query the INFORMATION_SCHEMA.PIPELINES_BATCHES_SUMMARY table for information on pipeline batch performance.

Examples

Example 1 - Replicate Collections using SQL

The following example replicates data from an existing MongoDB® Atlas cluster into SingleStore.

Create a link to the MongoDB® endpoint, for example, the primary node of a MongoDB® Atlas cluster.

SQL

CREATE LINK <linkname> AS MONGODB
CONFIG '{"mongodb.hosts":"<Hostname>",
"collection.include.list": "<Collection list>",
"mongodb.ssl.enabled":"true",
"mongodb.authsource":"admin"}'
CREDENTIALS '{"mongodb.user":"<username>",
"mongodb.password":"<password>"}';

Create tables in SingleStore.

SQL

## Infer tables from source
CREATE TABLES AS INFER PIPELINE AS LOAD DATA LINK <linkname> '*' FORMAT AVRO;

Once the link and the tables are created, run the following command to start all the pipelines and begin the data replication process:
SQL
```
## Start pipelines
START ALL PIPELINES;
```

To view the status of all the pipelines, query the information_schema.pipelines_cursors table. Run the following SQL statement to display the status of the replication task:

SQL

SELECT SOURCE_PARTITION_ID, 
 EARLIEST_OFFSET,
 LATEST_OFFSET,
 LATEST_EXPECTED_OFFSET-LATEST_OFFSET as DIFF,
 UPDATED_UNIX_TIMESTAMP 
FROM information_schema.pipelines_cursors;

Example 2 - Create Tables with Different Names from the Source Collection

To create tables in SingleStore with names that differ from the name of the source MongoDB® collection, use the following syntax:

SQL

CREATE TABLE <new_table_name> AS INFER PIPELINE AS LOAD DATA 
LINK <link_name> '<source_db.source_collection>' FORMAT AVRO;

You can also use this command to import collections if a table with the same name already exists in SingleStore. Additionally, you can use this syntax to reimport a collection with a distinct table name.

Load Data from MongoDB®

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Replicate MongoDB® Collections using SQL

Syntax

Parameters

Remarks

Source Database Requirements

CDC Snapshot Strategies

Configure Ingestion Speed Limit

Examples

Example 1 - Replicate Collections using SQL

Example 2 - Create Tables with Different Names from the Source Collection

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