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# Test race conditions involving:
# - s1: VACUUM inplace-updating a pg_class row
# - s2: GRANT/REVOKE making pg_class rows dead
# - s3: "VACUUM pg_class" making dead rows LP_UNUSED; DDL reusing them
# Need GRANT to make a non-HOT update. Otherwise, "VACUUM pg_class" would
# leave an LP_REDIRECT that persists. To get non-HOT, make rels so the
# pg_class row for vactest.orig50 is on a filled page (assuming BLCKSZ=8192).
# Just to save on filesystem syscalls, use relkind=c for every other rel.
setup
{
CREATE EXTENSION injection_points;
CREATE SCHEMA vactest;
CREATE FUNCTION vactest.mkrels(text, int, int) RETURNS void
LANGUAGE plpgsql SET search_path = vactest AS $$
DECLARE
tname text;
BEGIN
FOR i in $2 .. $3 LOOP
tname := $1 || i;
EXECUTE FORMAT('CREATE TYPE ' || tname || ' AS ()');
RAISE DEBUG '% at %', tname, ctid
FROM pg_class WHERE oid = tname::regclass;
END LOOP;
END
$$;
}
setup { VACUUM FULL pg_class; -- reduce free space }
setup
{
SELECT vactest.mkrels('orig', 1, 49);
CREATE TABLE vactest.orig50 ();
SELECT vactest.mkrels('orig', 51, 100);
}
teardown
{
DROP SCHEMA vactest CASCADE;
DROP EXTENSION injection_points;
}
# Wait during inplace update, in a VACUUM of vactest.orig50.
session s1
setup {
SELECT injection_points_set_local();
SELECT injection_points_attach('inplace-before-pin', 'wait');
}
step vac1 { VACUUM vactest.orig50; -- wait during inplace update }
# One bug scenario leaves two live pg_class tuples for vactest.orig50 and zero
# live tuples for one of the "intruder" rels. REINDEX observes the duplicate.
step read1 {
REINDEX TABLE pg_class; -- look for duplicates
SELECT reltuples = -1 AS reltuples_unknown
FROM pg_class WHERE oid = 'vactest.orig50'::regclass;
}
# Transactional updates of the tuple vac1 is waiting to inplace-update.
session s2
step grant2 { GRANT SELECT ON TABLE vactest.orig50 TO PUBLIC; }
step revoke2 { REVOKE SELECT ON TABLE vactest.orig50 FROM PUBLIC; }
step begin2 { BEGIN; }
step c2 { COMMIT; }
step r2 { ROLLBACK; }
# Non-blocking actions.
session s3
step vac3 { VACUUM pg_class; }
# Reuse the lp that vac1 is waiting to change. I've observed reuse at the 1st
# or 18th CREATE, so create excess.
step mkrels3 {
SELECT vactest.mkrels('intruder', 1, 100); -- repopulate LP_UNUSED
SELECT injection_points_detach('inplace-before-pin');
SELECT injection_points_wakeup('inplace-before-pin');
}
# target gains a successor at the last moment
permutation
vac1(mkrels3) # reads pg_class tuple T0 for vactest.orig50, xmax invalid
grant2 # T0 becomes eligible for pruning, T1 is successor
vac3 # T0 becomes LP_UNUSED
mkrels3 # vac1 wakes, scans to T1
read1
# target already has a successor, which commits
permutation
begin2
grant2 # T0.t_ctid = T1
vac1(mkrels3) # reads T0 for vactest.orig50
c2 # T0 becomes eligible for pruning
vac3 # T0 becomes LP_UNUSED
mkrels3 # vac1 wakes, scans to T1
read1
# target already has a successor, which becomes LP_UNUSED at the last moment
permutation
begin2
grant2 # T0.t_ctid = T1
vac1(mkrels3) # reads T0 for vactest.orig50
r2 # T1 becomes eligible for pruning
vac3 # T1 becomes LP_UNUSED
mkrels3 # reuse T1; vac1 scans to T0
read1
# target already has a successor, which becomes LP_REDIRECT at the last moment
permutation
begin2
grant2 # T0.t_ctid = T1, non-HOT due to filled page
vac1(mkrels3) # reads T0
c2
revoke2 # HOT update to T2
grant2 # HOT update to T3
vac3 # T1 becomes LP_REDIRECT
mkrels3 # reuse T2; vac1 scans to T3
read1
# waiting for updater to end
permutation
vac1(c2) # reads pg_class tuple T0 for vactest.orig50, xmax invalid
begin2
grant2 # T0.t_ctid = T1, non-HOT due to filled page
revoke2 # HOT update to T2
mkrels3 # vac1 awakes briefly, then waits for s2
c2
read1
# Another LP_UNUSED. This time, do change the live tuple. Final live tuple
# body is identical to original, at a different TID.
permutation
begin2
grant2 # T0.t_ctid = T1, non-HOT due to filled page
vac1(mkrels3) # reads T0
r2 # T1 becomes eligible for pruning
grant2 # T0.t_ctid = T2; T0 becomes eligible for pruning
revoke2 # T2.t_ctid = T3; T2 becomes eligible for pruning
vac3 # T0, T1 & T2 become LP_UNUSED
mkrels3 # reuse T0, T1 & T2; vac1 scans to T3
read1
# Another LP_REDIRECT. Compared to the earlier test, omit the last grant2.
# Hence, final live tuple body is identical to original, at a different TID.
permutation begin2 grant2 vac1(mkrels3) c2 revoke2 vac3 mkrels3 read1
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