System Limits

Cluster-Level Limits

Item	Max Spec (enforced)	Max Spec (recommended)	Comments
Number of hosts in a cluster	None	Workloads that generate significant network traffic between hosts should be limited to clusters with smaller number of hosts.
Number of nodes in a cluster (includes leaves and aggregators)	None	Workloads that generate significant network traffic between nodes should be limited to clusters with smaller number of nodes.
Number of databases in a cluster	None		Each database requires memory for transaction buffer and more databases implies greater demand on available memory.
Concurrent queries in a cluster	None		Each aggregator will only actually execute a limited number of queries at once (defined by max_connection_threads, default 192). Beyond that concurrency, queries will be queued up.
Simultaneous client connections	100,000 per aggregator		For more information, read about max_connections

Database-Level Limits

Item	Max Spec (enforced)	Comments
Number of tables in a database		Each table costs some per-table memory overhead.
Number of partitions in a cluster	None
Number of database partitions per node	2414

Table-Level Limits

Item	Max Spec (enforced)	Max Spec (recommended)	Comments
Number of columns per table	4096
Row size in bytes	64KB *		Limit does not apply to variable-length strings such as VARCHAR, VARBINARY, TEXT, etc.
Length of names in characters (applies to table names, column names)	64
Number of indexes per table	63
Number of columns per index	32
Number of tables in a join for each SELECT	253
Number of entries in a `SELECT` projection (target) list	12800
Number of nested sub-select queries using the `UNION` statement	337	40	Beyond 40 the `UNION` statements are converted to `TABLE` function.

* The number of fields that will fit in the 64KB maximum row size is determined by the field types and how rows are laid out in the in-memory rowstore format. In some cases, writes (inserts and updates) to columnstore tables are implemented by storing the newly written rows in a rowstore format before flushing them to the column-oriented format. The row size limit applies to fixed-width data which includes a 4-byte nullability flag for nullable fields. The row size limit does not include the body of variable-width fields, but only the in-row portion, which includes an 8-byte memory location pointer and an optional 4-byte nullability flag. The sum of the in-row data size for all columns cannot exceed 64KB."

Naming Constraints

Item	Constraints
General	Maximum length is 64 characters unless specified otherwise below. Name cannot be blank. Name cannot end with a space.
Database names	Database names can only contain alphanumeric characters and underscores, and cannot start with a digit.
Table names	Table names can contain both alphanumeric and non-alphanumeric characters, but cannot contain the `/` character.
Other database objects (stored procedures, views, user-defined functions, user-defined aggregate functions, and table-valued functions)	Maximum length of 64 characters.
User names	Maximum length of 32 characters.
Role names	No length limit. Cannot contain commas or spaces.
Group names	No length limit. Cannot contain commas or spaces.