OPTIMIZE

Optimize one or more tables explicitly.

Table of contents

Synopsis

OPTIMIZE TABLE table_ident [ PARTITION (partition_column=value [ , ... ]) ] [, ...]
[ WITH ( optimization_parameter [= value] [, ... ] ) ]

Description

The OPTIMIZE TABLE command optimizes tables and table partitions by merging the segments of a table or a partition and reducing their number. It is also used to upgrade tables and table partitions to the current version of the storage engine. This command will block until the optimization process is complete. If the connection to CrateDB is lost, the request will continue in the background, and any new requests will block until the previous optimization is complete.

The PARTITION clause can be used to only optimize specific partitions of a partitioned table. Specified values for all partition columns are required.

In case the PARTITION clause is omitted all open partitions will be optimized. Closed partitions are not optimized. For performance reasons doing that should be avoided if possible.

See Partitioned tables for more information on partitioned tables.

For further information see Optimization.

Note

System tables cannot be optimized.

Parameters

table_ident

The name (optionally schema-qualified) of an existing table that is to be optimized.

Clauses

PARTITION

If the table is partitioned, the optional PARTITION clause can be used to optimize one partition exclusively.

[ PARTITION ( partition_column = value [ , ... ] ) ]

partition_column

One of the column names used for table partitioning.

value

The respective column value.

All partition columns (specified by the PARTITIONED BY clause) must be listed inside the parentheses along with their respective values using the partition_column = value syntax (separated by commas).

Because each partition corresponds to a unique set of partition column row values, this clause uniquely identifies a single partition to optimize.

Tip

The SHOW CREATE TABLE statement will show you the complete list of partition columns specified by the PARTITIONED BY clause.

WITH

The optional WITH clause can specify parameters for the optimization request.

[ WITH ( optimization_parameter [= value] [, ... ] ) ]

optimization_parameter

Specifies an optional parameter for the optimization request.

Available parameters are:

max_num_segments

The number of segments to merge to. To fully merge the table or partition set it to 1.

Defaults to simply checking if a merge is necessary, and if so, executes it.

Caution

Forcing a merge to a small number of segments can harm query performance if segments become too big.

If max_num_segments gets omitted, CrateDB will automatically determine the ideal number of segments based on internal criteria.

only_expunge_deletes

Should the merge process only expunge segments with deletes in it.

In CrateDB, a row is not deleted from a segment, just marked as deleted. During a merge process of segments, a new segment is created that does not have those deletes. This flag allows to only merge segments that have deletes.

Defaults to false.

flush

Instructs if a flush should be performed after the optimization.

Defaults to true.

upgrade_segments

This option is deprecated and has no effect anymore.