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Updating Statistics for Multiple Indexes

  • Couchbase Server 7.0
    +
    You can use the UPDATE STATISTICS statement to gather statistics for multiple indexes at once.

    Purpose

    The UPDATE STATISTICS statement provides a syntax which enables you to analyze multiple indexes at once. With this syntax, the statement gathers statistics for all the index key expressions from all specified indexes. This provides a shorthand so that you do not need to list all the index key expressions explicitly.

    If the same index expression is included in multiple indexes, duplicate index expressions are removed, so each index expression is only analyzed once.

    Syntax

    update-statistics-indexes ::=
      ( UPDATE STATISTICS [ FOR ] | ANALYZE [ KEYSPACE | COLLECTION ] )
      keyspace-ref indexes-clause [ index-using ] [ index-with ]
    ( 'UPDATE' 'STATISTICS' 'FOR'? | 'ANALYZE' ( 'KEYSPACE' | 'COLLECTION')? ) keyspace-ref indexes-clause index-using? index-with?

    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 | keyspace-partial
    keyspace-path ::= [ namespace ':' ] bucket [ '.' scope '.' collection ]
    ( namespace ':' )? bucket ( '.' scope '.' collection )?
    keyspace-partial ::= collection
    collection

    The simple name or fully-qualified name of the keyspace on which the indexes are built. Refer to the CREATE INDEX statement for details of the syntax.

    INDEX Clause

    indexes-clause ::= INDEX '(' index-name [ ',' index-name ]* | subquery-expr ')'
    'INDEX' '(' ( index-name ( ',' index-name )* | subquery-expr ) ')'

    For this syntax, the INDEX clause enables you to specify a comma-separated list of index names, or a subquery which returns an array of index names.

    index-name

    (Required) A unique name that identifies the index.

    Subquery Expression

    subquery-expr ::= '(' select ')'
    '(' select ')'

    Use parentheses to specify a subquery.

    The subquery must return an array of strings, each string representing the name of an index. The subquery should look for GSI indexes that are in the online state. Refer to Example 3 and Example 4 for details.

    USING Clause

    index-using ::= USING GSI
    'USING' 'GSI'

    In Couchbase Server 6.5 and later, the index type for a secondary index must be Global Secondary Index (GSI). The USING GSI keywords are optional and may be omitted.

    WITH Clause

    index-with ::= WITH expr
    'WITH' expr

    Use the WITH clause to specify additional options.

    expr

    An object with the following properties:

    sample_size

    [Optional] An integer specifying the sample size to use for distribution statistics. A minimum sample size is also calculated. If the specified sample size is smaller than the minimum sample size, the minimum sample size is used instead.

    resolution

    [Optional] A float representing the percentage of documents to store in each distribution bin. If omitted, the default value is 1.0, meaning each distribution bin contains 1% of the documents, and therefore 100 bins are required. The minimum resolution is 0.02 (5000 distribution bins) and the maximum is 5.0 (20 distribution bins).

    update_statistics_timeout

    [Optional] A number representing a duration in seconds. The command times out when this timeout period is reached. If omitted, a default timeout value is calculated based on the number of samples used.

    Refer to Distribution Statistics for more information on sample size and resolution.

    Result

    The statement returns an empty array.

    Examples

    Example 1. UPDATE STATISTICS with indexes
    UPDATE STATISTICS FOR `travel-sample`.inventory.airport
    INDEX (def_inventory_airport_faa, def_inventory_airport_city);
    Example 2. ANALYZE with indexes
    ANALYZE KEYSPACE `travel-sample`.inventory.airport
    INDEX (def_inventory_airport_faa, def_inventory_airport_city);

    This query is equivalent to the query in Example 1.

    Example 3. UPDATE STATISTICS with subquery
    UPDATE STATISTICS FOR `travel-sample`.inventory.airport INDEX (( (1)
      SELECT RAW name (2)
      FROM system:indexes
      WHERE state = "online"
        AND `using` = "gsi" (3)
        AND bucket_id = "travel-sample"
        AND scope_id = "inventory"
        AND keyspace_id = "airport" ));
    1 One set of parentheses delimits the whole group of index terms, and the other set of parentheses delimits the subquery, leading to a double set of parentheses.
    2 The RAW keyword forces the subquery to return a flattened array of strings, each of which refers to an index name.
    3 Since USING is a reserved keyword, you need to surround it in backticks in the query.
    Example 4. ANALYZE with subquery
    ANALYZE KEYSPACE `travel-sample`.inventory.airport INDEX ((
      SELECT RAW name
      FROM system:indexes
      WHERE state = "online"
        AND `using` = "gsi"
        AND bucket_id = "travel-sample"
        AND scope_id = "inventory"
        AND keyspace_id = "airport" ));

    This query is equivalent to the query in Example 4.