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Update Statistics for a Single Index

  • reference
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    You can use the UPDATE STATISTICS statement to gather statistics on a single index.

    Purpose

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

    Syntax

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

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

    INDEX Clause

    index-clause ::= INDEX ( index-path '.' index-name | index-name ON keyspace-ref )
    'INDEX' ( index-path '.' index-name | index-name 'ON' keyspace-ref )

    For this syntax, the INDEX clause enables you to specify the index name and a keyspace.

    index-name

    (Required) A unique name that identifies the index.

    Index Path

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

    You can use a dotted notation to specify the index and the keyspace on which the index is built. Refer to the ALTER INDEX or DROP INDEX statements for details of the syntax.

    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

    Alternatively, you can use the index name with the ON keyword and a keyspace reference to specify the keyspace on which the index is built. Refer to the ALTER INDEX or DROP INDEX statements for details of the syntax.

    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.

    batch_size

    [Optional] Only applies when processing multiple index expressions at once. If there is a large number of index expressions to process, the cost-based optimizer deals with them in batches. This option is an integer specifying the maximum number of index expressions in each batch. If omitted, the default value is 10. You can specify a different value based on the memory availability of the system. Note that when index expressions are processed in batches, the update_statistics_timeout value (above) applies to each batch.

    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 index identifier
    UPDATE STATISTICS FOR
INDEX default:`travel-sample`.inventory.airport.def_inventory_airport_city;
    Example 2. UPDATE STATISTICS with ON clause
    UPDATE STATISTICS FOR
INDEX def_inventory_airport_city ON default:`travel-sample`.inventory.airport;

    This query is equivalent to the query in Example 1.

    Example 3. ANALYZE with index identifier
    ANALYZE INDEX default:`travel-sample`.inventory.airport.def_inventory_airport_city;

    This query is equivalent to the query in Example 1.

    Example 4. ANALYZE with ON clause
    ANALYZE INDEX def_inventory_airport_city ON default:`travel-sample`.inventory.airport;

    This query is equivalent to the query in Example 1.