是否可以暂时禁用 Postgres 中的索引？

Question

我想暂时禁用表中的一个索引，但我找不到任何文档表明它是可能的。

原因：我有一个索引，它可能会导致与它旨在加速的任何查询无关的查询问题。这是一个新的索引，自从它被引入以来，整个系统似乎变慢了。我只是希望能够可靠地消除它作为罪魁祸首，这似乎是最简单的方法，也欢迎其他解决方案建议以及更好的问题建议。

Answer 1

你可以戳系统目录来禁用索引：

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

这意味着索引不会用于查询，但仍会更新。它是用于并发索引构建的标志之一。请注意，我只是做了一个快速测试，看看索引是否仍然在更新，请注意。

Answer 2

begin;
drop index foo_ndx;
explain analyze select * from foo;
rollback;

我认为没有办法只禁用一个，尽管您可以在事务中执行此操作以使从中恢复非常简单。您还可以禁用 indexscan 以禁用所有索引。

另外，请确保您在查询时使用explain analyze。

Answer 3

我已经创建（并审查了）一个函数，它可以在各种情况下执行此操作。你肯定需要小心它，但它确实有效。

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
;