Delete Statistics

reference

Enterprise Edition
Couchbase Server 7.0

You can use the UPDATE STATISTICS statement to delete statistics.

Purpose

The UPDATE STATISTICS statement provides a syntax which enables you to delete statistics for a set of index expressions, or for an entire keyspace.

Since the cost-based optimizer uses statistics for cost calculations, deleting statistics for a set of index expressions effectively turns off the cost-based optimizer for queries which utilize predicates on those expressions. Deleting all statistics for a keyspace turns off the cost-based optimizer for all queries referencing that keyspace.

Syntax

update-statistics-delete ::=
  ( UPDATE STATISTICS [ FOR ] | ANALYZE [ KEYSPACE | COLLECTION ] )
    keyspace-ref delete-clause

( 'UPDATE' 'STATISTICS' 'FOR'? | 'ANALYZE' ( 'KEYSPACE' | 'COLLECTION')? ) keyspace-ref delete-clause

For this syntax, UPDATE STATISTICS and ANALYZE are synonyms. The statement must begin with one of these alternatives.

When using the UPDATE STATISTICS keywords, the FOR keyword is optional. Including this keyword makes no difference to the operation of the statement.

When using the ANALYZE keyword, the COLLECTION or KEYSPACE keywords are optional. Including either of these keywords makes no difference to the operation of the statement.

Keyspace Reference

keyspace-ref ::= keyspace-path | keyspace-partial

keyspace-path ::= [ namespace ':' ] bucket [ '.' scope '.' collection ]

( namespace ':' )? bucket ( '.' scope '.' collection )?

keyspace-partial ::= collection

The simple name or fully-qualified name of the keyspace for which you want to delete statistics. Refer to the CREATE INDEX statement for details of the syntax.

DELETE Clause

delete-clause ::= DELETE delete-expressions | delete-all

The DELETE clause enables you to provide a comma-separated list of index expressions for which you want to delete statistics, or to specify that you want to delete all statistics for the keyspace.

Delete Expressions

delete-expressions ::= [ STATISTICS ] '(' index-expr [ ',' index-expr ]* ')'

'STATISTICS'? '(' index-expr ( ',' index-expr )* ')'

If you used the UPDATE STATISTICS keywords at the beginning of the statement, you may not use the STATISTICS keyword in this clause.

Conversely, if you used the ANALYZE keyword at the beginning of the statement, you must include the STATISTICS keyword in this clause.

index-expr

The expression for which you want to delete statistics. This may be any expression that is supported as an index key, including, but not limited to:

A N1QL expression over any fields in the document, as used in a secondary index.
An array expression, as used when creating an array index.
An expression with the META() function, as used in a metadata index.

Delete All Statistics

delete-all ::= ALL | STATISTICS

If you used the UPDATE STATISTICS keywords at the beginning of the statement, you must use the ALL keyword in this clause.

Conversely, if you used the ANALYZE keyword at the beginning of the statement, you must use the STATISTICS keyword in this clause.

Result

The statement returns an empty array.

Examples

Example 1. Delete statistics with UPDATE STATISTICS

UPDATE STATISTICS FOR `travel-sample`.inventory.hotel
DELETE (city, country, free_breakfast);

Example 2. Delete statistics with ANALYZE

ANALYZE KEYSPACE `travel-sample`.inventory.hotel
DELETE STATISTICS (city, country, free_breakfast);

This query is equivalent to the query in Example 1.

Example 3. Delete all statistics with UPDATE STATISTICS

UPDATE STATISTICS FOR `travel-sample`.inventory.airport DELETE ALL;

Example 4. Delete all statistics with ANALYZE

ANALYZE KEYSPACE `travel-sample`.inventory.airport DELETE STATISTICS;

This query is equivalent to the query in Example 3.