Store XML explain plan in PostgreSQL database

问题

How can I store XML explain plan (or any other format) in PostgreSQL database?

Test data: explain (verbose, format xml) select 1

Table to store results: create table tmp.explain_plan_data (expp xml);

My naive test failed:

insert into tmp.explain_plan_data values (explain (verbose, format xml) select 1);

It seems that explain cannot be used in any other select statement, the following statement does not work either:

select * from (explain (verbose, format xml) select 1) a

We are using PostreSQL 9.1.6

回答1:

It is not possible to capture EXPLAIN output using subqueries, you should go for a PL/pgSQL procedure:

CREATE OR REPLACE FUNCTION explain_v_xml(in_sql text)
RETURNS TABLE(explain_line xml) AS $explain_v_xml$
BEGIN
    RETURN QUERY EXECUTE 'EXPLAIN (VERBOSE, FORMAT xml) '||in_sql;
END;
$explain_v_xml$ LANGUAGE plpgsql;

Now you can query it like this:

SELECT explain_line FROM explain_v_xml('SELECT * FROM pg_locks');

And insert into your target table:

INSERT INTO tmp.explain_plan_data SELECT explain_v_xml('SELECT 1');
SELECT * FROM tmp.explain_plan_data;

Perhaps explain output alone in the table is not so handy, I would rather added original query and timestamptz of the insert.

回答2:

I'm not 100% sure, but I think this only possible using a stored procedure. You could use the DO statement:

DO
$$
DECLARE
    _result xml;
BEGIN
    EXECUTE 'explain (verbose, format xml) select 1' INTO _result;

    INSERT INTO tmp.explain_plan_data(expp) VALUES(_result);
END;
$$;

来源：https://stackoverflow.com/questions/14747331/store-xml-explain-plan-in-postgresql-database

标签

xml

plpgsql

postgresql-9.1

explain