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.

Table 1: Schema object limits

Objects	Limit	Value	Explanation	Internal name	Error type
Database	Maximum path depth	32	Maximum number of nested path elements (directories, tables)	MaxDepth	SCHEME_ERROR
Database	Maximum number of paths (schema objects)	200,000	Maximum number of path elements (directories, tables) in the database	MaxPaths	GENERIC_ERROR
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 the maximum number of tablets in the database is reached, no automatic table sharding is performed	MaxShards	GENERIC_ERROR
Database	Maximum object name length	255	Limits the number of characters in the name of a schema object, such as a directory or table	MaxPathElementLength	SCHEME_ERROR
Database	Maximum ACL size	10 KB	Maximum total size of all access control rules that can be saved for a single schema object	MaxAclBytesSize	GENERIC_ERROR
Directory	Maximum number of objects	100,000	Maximum number of tables and child directories created in a directory	MaxChildrenInDir	SCHEME_ERROR
Table	Maximum number of table shards	35,000	Maximum number of table shards	MaxShardsInPath	GENERIC_ERROR
Table	Maximum number of columns	200	Limits the total number of columns in a table	MaxTableColumns	GENERIC_ERROR
Table	Maximum column name length	255	Limits the number of characters in the name of a column	MaxTableColumnNameLength	GENERIC_ERROR
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	GENERIC_ERROR
Table	Maximum number of indexes	20	Maximum number of indexes other than the primary key index that can be created in a table	MaxTableIndices	GENERIC_ERROR
Table	Maximum number of slaves	3	Maximum number of read-only replicas that can be specified when creating a table with slaves	MaxSlavesCount	GENERIC_ERROR
Table	Maximum number of tables to copy	1000	Limit on the size of the list of tables for persistent table copy operations	MaxConsistentCopyTargets	GENERIC_ERROR

Size limits for stored data

Table 2: 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	8 MB	GENERIC_ERROR

Limits that apply when executing queries

The table below lists the limits that apply to query execution. The Call column specifies the public API call that will end with the error status specified in the Status column.

Table 3: Limits that apply when executing queries

Parameter	Value	Call	Explanation	Status in case of a violation of the limit
Maximum number of rows in query results	1000	ExecuteDataQuery	Complete results of some queries executed using the ExecuteDataQuery method may contain more rows than allowed. In this case, the maximum allowed number of rows will be returned in response to the query and the result will have the flag truncated	SUCCESS
Maximum query result size	50 MB	ExecuteDataQuery	Complete results of some queries may exceed the set limit. In this case, the query fails and no data is returned	PRECONDITION_FAILED
Maximum number of sessions per cluster node	1000	CreateSession	Using the library for working with YDB, an application can create sessions within a connection. Sessions are linked to a node. You can create a limited number of sessions with a single node	OVERLOADED
Maximum query text length	10 KB	ExecuteDataQuery	Limit on the length of YQL query text	BAD_REQUEST
Maximum size of parameter values	50 MB	ExecuteDataQuery	Limit on the total size of parameters passed when executing a previously prepared query	BAD_REQUEST