PostgreSQL Query Plan – Get Query Plan for SQL Statement in PL/pgSQL Function

functionsperformanceplpgsqlpostgresql

It's possible when using the pgadmin or plsql to get a hold of a query plan for a sql statement executed inside a user defined function (UDF) using EXPLAIN. So how do I get hold of the query plan for a particular invocation of a UDF? I see the UDF abstracted away into a single operation F() in pgadmin.

I have looked at documentation but I couldn't find anything.

Currently I'm pulling out the statements and running them manually. But this isn't going to cut it for large queries.

For example, consider the UDF below. This UDF, even though it has the ability to print out its query string, will not work with a copy-paste as it has a local created temporary table, which does not exist when you paste and execute it.

CREATE OR REPLACE FUNCTION get_paginated_search_results(
    forum_id_ INTEGER,
    query_    CHARACTER VARYING,
    from_date_ TIMESTAMP WITHOUT TIME ZONE DEFAULT NULL,
    to_date_ TIMESTAMP WITHOUT TIME ZONE DEFAULT NULL,
    in_categories_ INTEGER[] DEFAULT '{}')
RETURNS SETOF post_result_entry AS $$
DECLARE
    join_string CHARACTER VARYING := ' ';
    from_where_date CHARACTER VARYING := ' ';
    to_where_date CHARACTER VARYING := ' ';
    query_string_ CHARACTER VARYING := ' ';
BEGIN
    IF NOT from_date_ IS NULL THEN
        from_where_date := ' AND fp.posted_at > ''' || from_date_ || '''';
    END IF;

    IF NOT to_date_ IS NULL THEN
        to_where_date := ' AND fp.posted_at < ''' || to_date_ || '''';
    END IF;

    CREATE LOCAL TEMP TABLE un_cat(id) ON COMMIT DROP AS (select * from unnest(in_categories_)) ;

    if in_categories_ != '{}' THEN
        join_string := ' INNER JOIN forum_topics ft ON fp.topic_id = ft.id ' ||
        ' INNER JOIN un_cat uc ON uc.id = ft.category_id ' ;
    END IF;

    query_string_ := '
    SELECT index,posted_at,post_text,name,join_date,quotes
    FROM forum_posts fp
    INNER JOIN forum_user fu ON
    fu.forum_id = fp.forum_id AND fu.id = fp.user_id' ||
        join_string
    ||
    'WHERE fu.forum_id = ' || forum_id_ || ' AND
    to_tsvector(''english'',fp.post_text) @@ to_tsquery(''english'','''|| query_||''')' || 
        from_where_date || 
        to_where_date
    ||';';

    RAISE NOTICE '%', query_string_ ;

    RETURN QUERY
    EXECUTE query_string_;
END;
$$ LANGUAGE plpgsql;

Best Answer

You should be able to use auto-explain. Turn it on and

SET auto_explain.log_min_duration = 0;

and you should get the plans in your log for all statements run in that session.

You might also want to set

SET auto_explain.log_analyze = true; but you'll essentially run everything double - once for 'real' and once to EXPLAIN ANALYZE on. During a non-timing performance testing phase, this output can be much more useful than EXPLAIN plans alone, as it provides what plan actually happened.

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