Is it possible to temporarily disable an index in Postgres?

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失恋的感觉
失恋的感觉 2021-01-30 03:57

I have got one index on a table that I would like to temporarily disable, I can\'t find any documentation suggesting that it\'s possible, though.

Reason: I\'ve got an in

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  • 2021-01-30 04:32

    You can poke the system catalogue to disable an index:

    update pg_index set indisvalid = false where indexrelid = 'test_pkey'::regclass
    

    This means that the index won't be used for queries but will still be updated. It's one of the flags used for concurrent index building. Note that I've only done a quick test to see if the index still seems to be updated, caveat emptor.

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  • 2021-01-30 04:38
    begin;
    drop index foo_ndx;
    explain analyze select * from foo;
    rollback;
    

    I don't think there is a way to disable just one, though you can do this in a transaction to make recovering from it dead simple. You can also disable indexscan to disable all indices.

    Also, make sure you are doing explain analyze on your queries.

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  • 2021-01-30 04:40

    I've created (and vetted) a function that does this for a wide variety of circumstances. You definitely need to be careful with it, but it does work.

    CREATE OR REPLACE PROCEDURE global.enable_indexes(
        IN schema_name TEXT
    ,   IN table_name TEXT
    ,   IN index_name TEXT
    ,   IN enable_use BOOLEAN
    ,   IN enable_updates BOOLEAN
    ,   IN skip_essentials BOOLEAN DEFAULT TRUE
    ) AS
    $$
    DECLARE
        each_record RECORD;
    BEGIN
    
    /*
    USAGE:
    
    schema_name:
    - filters down by schema name
    - if NULL then does not filter
    table_name:
    - filters down by table name (careful - not schema qualified)
    - if NULL then does not filter
    index_name:
    - filters down by index name (careful - not schema qualified)
    - if NULL then does not filter
    enable_use:
    - This SETs the index as being available for use.
    - If enable_updates is FALSE, then automatically FALSE
    enable_updates:
    - This SETs the index to be updated (which doesn't imply that it is enabled for use)
    - When this was previously FALSE for the given index, then when setting to true will also trigger a rebuild of the index
    skip_essentials:
    - When this is true, PRIMARY and UNIQUE indexes will not be included in the scope (no changes).
    - Optional
    */
    
    
    IF array_replace(ARRAY[schema_name, table_name, index_name], NULL, '') <@ ARRAY[''] THEN
        RAISE EXCEPTION 'Error: Must specify at least one of schema_name | table_name | index_name';
    END IF;
    
    IF enable_updates IS FALSE THEN
        enable_use := FALSE;
        RAISE INFO 'FYI: Because enable_updates is FALSE, then likewise enable_use must be as well';
    END IF;
    
    FOR each_record IN
        select
            indexrelid
        ,   (schemaname||'.'||indexname) as index_name
        ,   indisvalid
        ,   indisready
        ,   (schemaname||'.'||tablename) as table_name
        ,   (CASE WHEN indisready IS FALSE and enable_use IS TRUE AND enable_updates IS TRUE THEN TRUE ELSE FALSE END) as needs_rebuilding
        FROM pg_indexes, pg_index
        WHERE
            indexrelid = (schemaname||'.'||indexname)::regclass
        AND case when schema_name <> '' THEN schemaname = schema_name ELSE TRUE END
        AND case when table_name <> '' THEN tablename = table_name ELSE TRUE END
        AND case when index_name <> '' THEN indexname = index_name ELSE TRUE END
        AND case when true THEN least(indisprimary, indisunique) = FALSE ELSE TRUE END
        AND case when skip_essentials THEN least(indisprimary, indisunique) = FALSE ELSE TRUE END
    LOOP
        BEGIN
    
        RAISE INFO 'Set index % to have use % and updates %.'
            ,   each_record.index_name
            ,   (case when each_record.indisvalid AND enable_use THEN 'enabled (not changed)' WHEN NOT each_record.indisvalid AND enable_use THEN 'enabled (changed)' else 'disabled' END)
            ,   (case when each_record.indisready AND enable_updates THEN 'enabled (not changed)' WHEN NOT each_record.indisready AND enable_updates THEN 'enabled (changed)' else 'disabled' END)
        ;
    
        UPDATE pg_index
        SET
            indisvalid = enable_use
        ,   indisready = enable_updates
        WHERE
            indexrelid = each_record.indexrelid
        ;
    
        IF each_record.needs_rebuilding THEN
            RAISE INFO '... Reindexing and Analyzing %', each_record.index_name;
            EXECUTE format('REINDEX INDEX %1$s; ANALYZE %2$s;', each_record.index_name, each_record.table_name);
        END IF;
    
        COMMIT;
    
        END;
    
    END LOOP;
    
    END
    $$
    LANGUAGE plpgsql
    ;
    
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