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c2a4078eba
The topic of turning EXPLAIN's BUFFERS option on with the ANALYZE option has come up a few times over the past few years. In many ways, doing this seems like a good idea as it may be more obvious to users why a given query is running more slowly than they might expect. Also, from my own (David's) personal experience, I've seen users posting to the mailing lists with two identical plans, one slow and one fast asking why their query is sometimes slow. In many cases, this is due to additional reads. Having BUFFERS on by default may help reduce some of these questions, and if not, make it more obvious to the user before they post, or save a round-trip to the mailing list when additional I/O effort is the cause of the slowness. The general consensus is that we want BUFFERS on by default with ANALYZE. However, there were more than zero concerns raised with doing so. The primary reason against is the additional verbosity, making it harder to read large plans. Another concern was that buffer information isn't always useful so may not make sense to have it on by default. It's currently December, so let's commit this to see if anyone comes forward with a strong objection against making this change. We have over half a year remaining in the v18 cycle where we could still easily consider reverting this if someone were to come forward with a convincing enough reason as to why doing this is a bad idea. There were two patches independently submitted to achieve this goal, one by me and the other by Guillaume. This commit is a mix of both of these patches with some additional work done by me to adjust various additional places in the documentation which include EXPLAIN ANALYZE output. Author: Guillaume Lelarge, David Rowley Reviewed-by: Robert Haas, Greg Sabino Mullane, Michael Christofides Discussion: https://postgr.es/m/CANNMO++W7MM8T0KyXN3ZheXXt-uLVM3aEtZd+WNfZ=obxffUiA@mail.gmail.com
138 lines
4.8 KiB
PL/PgSQL
138 lines
4.8 KiB
PL/PgSQL
--
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-- SELECT_INTO
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--
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SELECT *
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INTO TABLE sitmp1
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FROM onek
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WHERE onek.unique1 < 2;
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DROP TABLE sitmp1;
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SELECT *
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INTO TABLE sitmp1
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FROM onek2
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WHERE onek2.unique1 < 2;
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DROP TABLE sitmp1;
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--
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-- SELECT INTO and INSERT permission, if owner is not allowed to insert.
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--
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CREATE SCHEMA selinto_schema;
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CREATE USER regress_selinto_user;
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ALTER DEFAULT PRIVILEGES FOR ROLE regress_selinto_user
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REVOKE INSERT ON TABLES FROM regress_selinto_user;
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GRANT ALL ON SCHEMA selinto_schema TO public;
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SET SESSION AUTHORIZATION regress_selinto_user;
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-- WITH DATA, passes.
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CREATE TABLE selinto_schema.tbl_withdata1 (a)
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AS SELECT generate_series(1,3) WITH DATA;
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INSERT INTO selinto_schema.tbl_withdata1 VALUES (4);
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EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF, BUFFERS OFF)
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CREATE TABLE selinto_schema.tbl_withdata2 (a) AS
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SELECT generate_series(1,3) WITH DATA;
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-- WITH NO DATA, passes.
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CREATE TABLE selinto_schema.tbl_nodata1 (a) AS
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SELECT generate_series(1,3) WITH NO DATA;
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EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF)
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CREATE TABLE selinto_schema.tbl_nodata2 (a) AS
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SELECT generate_series(1,3) WITH NO DATA;
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-- EXECUTE and WITH DATA, passes.
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PREPARE data_sel AS SELECT generate_series(1,3);
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CREATE TABLE selinto_schema.tbl_withdata3 (a) AS
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EXECUTE data_sel WITH DATA;
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EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF)
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CREATE TABLE selinto_schema.tbl_withdata4 (a) AS
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EXECUTE data_sel WITH DATA;
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-- EXECUTE and WITH NO DATA, passes.
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CREATE TABLE selinto_schema.tbl_nodata3 (a) AS
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EXECUTE data_sel WITH NO DATA;
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EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF, BUFFERS OFF)
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CREATE TABLE selinto_schema.tbl_nodata4 (a) AS
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EXECUTE data_sel WITH NO DATA;
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RESET SESSION AUTHORIZATION;
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ALTER DEFAULT PRIVILEGES FOR ROLE regress_selinto_user
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GRANT INSERT ON TABLES TO regress_selinto_user;
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SET SESSION AUTHORIZATION regress_selinto_user;
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RESET SESSION AUTHORIZATION;
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DEALLOCATE data_sel;
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DROP SCHEMA selinto_schema CASCADE;
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DROP USER regress_selinto_user;
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-- Tests for WITH NO DATA and column name consistency
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CREATE TABLE ctas_base (i int, j int);
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INSERT INTO ctas_base VALUES (1, 2);
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CREATE TABLE ctas_nodata (ii, jj, kk) AS SELECT i, j FROM ctas_base; -- Error
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CREATE TABLE ctas_nodata (ii, jj, kk) AS SELECT i, j FROM ctas_base WITH NO DATA; -- Error
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CREATE TABLE ctas_nodata (ii, jj) AS SELECT i, j FROM ctas_base; -- OK
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CREATE TABLE ctas_nodata_2 (ii, jj) AS SELECT i, j FROM ctas_base WITH NO DATA; -- OK
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CREATE TABLE ctas_nodata_3 (ii) AS SELECT i, j FROM ctas_base; -- OK
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CREATE TABLE ctas_nodata_4 (ii) AS SELECT i, j FROM ctas_base WITH NO DATA; -- OK
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SELECT * FROM ctas_nodata;
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SELECT * FROM ctas_nodata_2;
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SELECT * FROM ctas_nodata_3;
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SELECT * FROM ctas_nodata_4;
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DROP TABLE ctas_base;
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DROP TABLE ctas_nodata;
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DROP TABLE ctas_nodata_2;
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DROP TABLE ctas_nodata_3;
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DROP TABLE ctas_nodata_4;
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--
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-- CREATE TABLE AS/SELECT INTO as last command in a SQL function
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-- have been known to cause problems
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--
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CREATE FUNCTION make_table() RETURNS VOID
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AS $$
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CREATE TABLE created_table AS SELECT * FROM int8_tbl;
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$$ LANGUAGE SQL;
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SELECT make_table();
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SELECT * FROM created_table;
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-- Try EXPLAIN ANALYZE SELECT INTO and EXPLAIN ANALYZE CREATE TABLE AS
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-- WITH NO DATA, but hide the outputs since they won't be stable.
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DO $$
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BEGIN
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EXECUTE 'EXPLAIN ANALYZE SELECT * INTO TABLE easi FROM int8_tbl';
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EXECUTE 'EXPLAIN ANALYZE CREATE TABLE easi2 AS SELECT * FROM int8_tbl WITH NO DATA';
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END$$;
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DROP TABLE created_table;
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DROP TABLE easi, easi2;
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--
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-- Disallowed uses of SELECT ... INTO. All should fail
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--
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DECLARE foo CURSOR FOR SELECT 1 INTO int4_tbl;
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COPY (SELECT 1 INTO frak UNION SELECT 2) TO 'blob';
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SELECT * FROM (SELECT 1 INTO f) bar;
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CREATE VIEW foo AS SELECT 1 INTO int4_tbl;
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INSERT INTO int4_tbl SELECT 1 INTO f;
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-- Test CREATE TABLE AS ... IF NOT EXISTS
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CREATE TABLE ctas_ine_tbl AS SELECT 1;
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CREATE TABLE ctas_ine_tbl AS SELECT 1 / 0; -- error
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CREATE TABLE IF NOT EXISTS ctas_ine_tbl AS SELECT 1 / 0; -- ok
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CREATE TABLE ctas_ine_tbl AS SELECT 1 / 0 WITH NO DATA; -- error
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CREATE TABLE IF NOT EXISTS ctas_ine_tbl AS SELECT 1 / 0 WITH NO DATA; -- ok
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EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF)
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CREATE TABLE ctas_ine_tbl AS SELECT 1 / 0; -- error
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EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF)
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CREATE TABLE IF NOT EXISTS ctas_ine_tbl AS SELECT 1 / 0; -- ok
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EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF)
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CREATE TABLE ctas_ine_tbl AS SELECT 1 / 0 WITH NO DATA; -- error
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EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF)
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CREATE TABLE IF NOT EXISTS ctas_ine_tbl AS SELECT 1 / 0 WITH NO DATA; -- ok
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PREPARE ctas_ine_query AS SELECT 1 / 0;
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EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF)
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CREATE TABLE ctas_ine_tbl AS EXECUTE ctas_ine_query; -- error
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EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF)
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CREATE TABLE IF NOT EXISTS ctas_ine_tbl AS EXECUTE ctas_ine_query; -- ok
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DROP TABLE ctas_ine_tbl;
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