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
Database	Maximum path depth	32	Maximum number of nested path elements (directories, tables).	MaxDepth	SCHEME_ERROR
Database	Maximum number of paths (schema objects)	10,000	Maximum number of path elements (directories, tables) in a 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 a database reaches the maximum number of tablets, no automatic table sharding takes place.	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 a table	MaxPathElementLength	SCHEME_ERROR
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	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 a column name	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 followers	3	Maximum number of read-only replicas that can be specified when creating a table with followers.	MaxFollowersCount	GENERIC_ERROR
Table	Maximum number of tables to copy	10,000	Limit on the size of the table list for persistent table copy operations	MaxConsistentCopyTargets	GENERIC_ERROR

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	Status in case of a violation of the limit
Query duration	1800 seconds (30 minutes)	The maximum amount of time allowed for a single query to execute.	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.	OVERLOADED
Maximum query text length	10 KB	The maximum allowable length of YQL query text.	BAD_REQUEST
Maximum size of parameter values	50 MB	The maximum total size of parameters passed when executing a previously prepared query.	BAD_REQUEST

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

Topic limits

Parameter	Value
Maximum size of a transmitted message	12 MB