Database Limits

This section describes the parameters of limits set in YDB.

Schema Object Limits

The table below shows the limits that apply to schema objects: tables, databases, and columns. The "Object" column specifies the type of schema object that the limit applies to.
The "Error type" column shows the status that the query ends with if an error occurs. For more information about statuses, see Error handling in the API.

Objects	Limit	Value	Explanation	Internal name	Error type	Error message
Database	Maximum path depth	32	Maximum number of nested path elements (directories, tables).	MaxDepth	SCHEME_ERROR	Paths depth limit exceeded
Database	Maximum number of paths (schema objects)	10,000	Maximum number of path elements (directories, tables) in a database.	MaxPaths	PRECONDITION_FAILED	Paths count limit exceeded
Database	Maximum number of tablets	200,000	Maximum number of tablets (table shards and system tablets) that can run in the database. An error is returned if a query to create, copy, or update a table exceeds this limit. When a database reaches the maximum number of tablets, no automatic table sharding takes place.	MaxShards	PRECONDITION_FAILED	Shards count limit exceeded (in subdomain)
Database	Maximum object name length	255	Limits the number of characters in the name of a schema object, such as a directory or a table.	MaxPathElementLength	SCHEME_ERROR	Path part is too long
Database	Maximum ACL size	10 KB	Maximum total size of all access control rules that can be saved for the schema object in question.	MaxAclBytesSize	BAD_REQUEST	ACL size limit exceeded
Directory	Maximum number of objects	100,000	Maximum number of tables and child directories created in a directory.	MaxChildrenInDir	PRECONDITION_FAILED	Children count limit exceeded
Table	Maximum number of table shards	35,000	Maximum number of table shards.	MaxShardsInPath	PRECONDITION_FAILED	Shards count limit exceeded (in dir)
Table	Maximum number of columns	200	Limits the total number of columns in a table.	MaxTableColumns	SCHEME_ERROR on CREATE / BAD_REQUEST on ALTER	Too many columns
Table	Maximum column name length	255	Limits the number of characters in a column name.	MaxTableColumnNameLength	SCHEME_ERROR	Column name too long
Table	Maximum number of columns in a primary key	20	Each table must have a primary key. The number of columns in the primary key may not exceed this limit.	MaxTableKeyColumns	SCHEME_ERROR	Too many key columns
Table	Maximum number of indexes	20	Maximum number of indexes other than the primary key index that can be created in a table.	MaxTableIndices	PRECONDITION_FAILED	Indexes count has reached maximum value in the table
Table	Maximum number of followers	3	Maximum number of read-only replicas that can be specified when creating a table with followers.	MaxFollowersCount	BAD_REQUEST	Too much followers
Table	Maximum number of tables to copy	10,000	Limit on the size of the table list for persistent table copy operations.	MaxConsistentCopyTargets	BAD_REQUEST	Consistent copy object count limit exceeded

Size Limits for Stored Data

Parameter	Value	Error type
Maximum total size of all columns in a primary key	1 MB	GENERIC_ERROR
Maximum size of a string column value	16 MB	GENERIC_ERROR

Analytical Table Limits

Parameter	Value
Maximum row size	8 MB
Maximum size of an inserted data block	8 MB

Limits on Query Execution

The table below lists the limits that apply to query execution.

Parameter	Default	Explanation	Effect in case of a violation of the limit
Query duration	2 hours	The maximum amount of time allowed for a single query to execute.	Returns status code `TIMEOUT`
Maximum number of sessions per cluster node	1,000	The limit on the number of sessions that clients can create with each YDB node.	Returns status code `OVERLOADED`
Maximum query text length	10 KB	The maximum allowable length of YQL query text.	Returns status code `BAD_REQUEST`
Maximum size of parameter values	50 MB	The maximum total size of parameters passed when executing a previously prepared query.	Returns status code `BAD_REQUEST`
Maximum size of a row	50 MB	The maximum total size of all fields of a single row returned or produced by the query.	Returns status code `PRECONDITION_FAILED`
Maximum number of locks per DataShard	10,000	The number of lock ranges per DataShard	Converts some locks to whole-shard locks, which use less memory but lock the entire shard instead of just a part.

Legacy Limits

In previous versions of YDB, queries were typically executed using an API called "Table Service". This API had the following limitations, which have been addressed by replacing it with a new API called "Query Service".

Parameter	Default	Explanation	Status in case of a violation of the limit
Maximum number of rows in query results	1,000	The complete results of some queries executed using the `ExecuteDataQuery` method may contain more rows than allowed. In such cases, the query will return the maximum number of rows allowed, and the result will have the `truncated` flag set.	SUCCESS
Maximum query result size	50 MB	The complete results of some queries may exceed the set limit. If this occurs, the query will fail and return no data.	PRECONDITION_FAILED

Resource pool limits

Parameter	Value
Maximum number of resource pool classifiers	1000

Limits on resource counts are also constrained by schema object limits. See above.

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