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cb5b28613d
Commit 147e3722f7 changed Tid scan so that it calls table_beginscan()
and uses the scan option for seq scan. This change caused two issues.
(1) The change caused Tid scan to take a predicate lock on the entire
relation in serializable transaction even when relation-level
lock is not necessary. This could lead to an unexpected
serialization error.
(2) The change caused Tid scan to increment the number of seq_scan
in pg_stat_*_tables views even though it's not seq scan. This
could confuse the users.
This commit adds the scan option for Tid scan and makes Tid scan
use it, to avoid those issues.
Back-patch to v12, where the bug was introduced.
Author: Tatsuhito Kasahara
Reviewed-by: Kyotaro Horiguchi, Masahiko Sawada, Fujii Masao
Discussion: https://postgr.es/m/CAP0=ZVKy+gTbFmB6X_UW0pP3WaeJ-fkUWHoD-pExS=at3CY76g@mail.gmail.com
105 lines
3.5 KiB
PL/PgSQL
105 lines
3.5 KiB
PL/PgSQL
-- tests for tidscans
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CREATE TABLE tidscan(id integer);
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-- only insert a few rows, we don't want to spill onto a second table page
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INSERT INTO tidscan VALUES (1), (2), (3);
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-- show ctids
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SELECT ctid, * FROM tidscan;
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-- ctid equality - implemented as tidscan
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EXPLAIN (COSTS OFF)
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SELECT ctid, * FROM tidscan WHERE ctid = '(0,1)';
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SELECT ctid, * FROM tidscan WHERE ctid = '(0,1)';
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EXPLAIN (COSTS OFF)
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SELECT ctid, * FROM tidscan WHERE '(0,1)' = ctid;
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SELECT ctid, * FROM tidscan WHERE '(0,1)' = ctid;
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-- OR'd clauses
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EXPLAIN (COSTS OFF)
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SELECT ctid, * FROM tidscan WHERE ctid = '(0,2)' OR '(0,1)' = ctid;
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SELECT ctid, * FROM tidscan WHERE ctid = '(0,2)' OR '(0,1)' = ctid;
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-- ctid = ScalarArrayOp - implemented as tidscan
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EXPLAIN (COSTS OFF)
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SELECT ctid, * FROM tidscan WHERE ctid = ANY(ARRAY['(0,1)', '(0,2)']::tid[]);
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SELECT ctid, * FROM tidscan WHERE ctid = ANY(ARRAY['(0,1)', '(0,2)']::tid[]);
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-- ctid != ScalarArrayOp - can't be implemented as tidscan
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EXPLAIN (COSTS OFF)
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SELECT ctid, * FROM tidscan WHERE ctid != ANY(ARRAY['(0,1)', '(0,2)']::tid[]);
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SELECT ctid, * FROM tidscan WHERE ctid != ANY(ARRAY['(0,1)', '(0,2)']::tid[]);
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-- tid equality extracted from sub-AND clauses
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EXPLAIN (COSTS OFF)
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SELECT ctid, * FROM tidscan
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WHERE (id = 3 AND ctid IN ('(0,2)', '(0,3)')) OR (ctid = '(0,1)' AND id = 1);
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SELECT ctid, * FROM tidscan
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WHERE (id = 3 AND ctid IN ('(0,2)', '(0,3)')) OR (ctid = '(0,1)' AND id = 1);
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-- nestloop-with-inner-tidscan joins on tid
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SET enable_hashjoin TO off; -- otherwise hash join might win
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EXPLAIN (COSTS OFF)
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SELECT t1.ctid, t1.*, t2.ctid, t2.*
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FROM tidscan t1 JOIN tidscan t2 ON t1.ctid = t2.ctid WHERE t1.id = 1;
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SELECT t1.ctid, t1.*, t2.ctid, t2.*
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FROM tidscan t1 JOIN tidscan t2 ON t1.ctid = t2.ctid WHERE t1.id = 1;
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EXPLAIN (COSTS OFF)
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SELECT t1.ctid, t1.*, t2.ctid, t2.*
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FROM tidscan t1 LEFT JOIN tidscan t2 ON t1.ctid = t2.ctid WHERE t1.id = 1;
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SELECT t1.ctid, t1.*, t2.ctid, t2.*
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FROM tidscan t1 LEFT JOIN tidscan t2 ON t1.ctid = t2.ctid WHERE t1.id = 1;
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RESET enable_hashjoin;
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-- exercise backward scan and rewind
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BEGIN;
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DECLARE c CURSOR FOR
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SELECT ctid, * FROM tidscan WHERE ctid = ANY(ARRAY['(0,1)', '(0,2)']::tid[]);
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FETCH ALL FROM c;
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FETCH BACKWARD 1 FROM c;
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FETCH FIRST FROM c;
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ROLLBACK;
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-- tidscan via CURRENT OF
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BEGIN;
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DECLARE c CURSOR FOR SELECT ctid, * FROM tidscan;
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FETCH NEXT FROM c; -- skip one row
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FETCH NEXT FROM c;
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-- perform update
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EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF)
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UPDATE tidscan SET id = -id WHERE CURRENT OF c RETURNING *;
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FETCH NEXT FROM c;
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-- perform update
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EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF)
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UPDATE tidscan SET id = -id WHERE CURRENT OF c RETURNING *;
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SELECT * FROM tidscan;
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-- position cursor past any rows
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FETCH NEXT FROM c;
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-- should error out
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EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF)
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UPDATE tidscan SET id = -id WHERE CURRENT OF c RETURNING *;
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ROLLBACK;
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-- bulk joins on CTID
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-- (these plans don't use TID scans, but this still seems like an
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-- appropriate place for these tests)
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EXPLAIN (COSTS OFF)
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SELECT count(*) FROM tenk1 t1 JOIN tenk1 t2 ON t1.ctid = t2.ctid;
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SELECT count(*) FROM tenk1 t1 JOIN tenk1 t2 ON t1.ctid = t2.ctid;
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SET enable_hashjoin TO off;
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EXPLAIN (COSTS OFF)
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SELECT count(*) FROM tenk1 t1 JOIN tenk1 t2 ON t1.ctid = t2.ctid;
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SELECT count(*) FROM tenk1 t1 JOIN tenk1 t2 ON t1.ctid = t2.ctid;
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RESET enable_hashjoin;
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-- check predicate lock on CTID
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BEGIN ISOLATION LEVEL SERIALIZABLE;
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SELECT * FROM tidscan WHERE ctid = '(0,1)';
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-- locktype should be 'tuple'
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SELECT locktype, mode FROM pg_locks WHERE pid = pg_backend_pid() AND mode = 'SIReadLock';
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ROLLBACK;
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DROP TABLE tidscan;
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