Multiple Adaptive Hash Search Partitions

The InnoDB adaptive hash index can have contention issues on multi-core systems when you run a mix of read and write queries that need to scan secondary indexes. This feature splits the adaptive hash index across several partitions to avoid such problems.

The number of adaptive hash partitions specified by the variable innodb_adaptive_hash_index_partitions are created, and hash indexes are assigned to each one based on index_id. This should help to solve contention problems in the adaptive hash search process when they occur.

Version Specific Information

Percona Server Version Comments 5.5.8-20.0 Initially released.

System Variables

variable innodb_adaptive_hash_index_partitions

Version Info:

• 5.5.8-20.0 – Introduced

Command Line:

Yes

Config File:

Yes

Scope:

Global

Dynamic:

No

Variable Type:

Numeric

Def :

1

Range:

1-64, (on 32-bit platform 1-32)

Specifies the number of partitions to use in the adaptive hash search process.

When set to one, no extra partitions are created and the normal process is in effect. When greater than one, the specified number of partitions are created across which to perform the adaptive search.

Other reading

• Index lock and adaptive search