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Tom Lane 8aa3e47510 Account for catalog snapshot in PGXACT->xmin updates. ... The CatalogSnapshot was not plugged into SnapshotResetXmin()'s accounting for whether MyPgXact->xmin could be cleared or advanced. In normal transactions this was masked by the fact that the transaction snapshot would be older, but during backend startup and certain utility commands it was possible to re-use the CatalogSnapshot after MyPgXact->xmin had been cleared, meaning that recently-deleted rows could be pruned even though this snapshot could still see them, causing unexpected catalog lookup failures. This effect appears to be the explanation for a recent failure on buildfarm member piculet. To fix, add the CatalogSnapshot to the RegisteredSnapshots heap whenever it is valid. In the previous logic, it was possible for the CatalogSnapshot to remain valid across waits for client input, but with this change that would mean it delays advance of global xmin in cases where it did not before. To avoid possibly causing new table-bloat problems with clients that sit idle for long intervals, add code to invalidate the CatalogSnapshot before waiting for client input. (When the backend is busy, it's unlikely that the CatalogSnapshot would be the oldest snap for very long, so we don't worry about forcing early invalidation of it otherwise.) In passing, remove the CatalogSnapshotStale flag in favor of using "CatalogSnapshot != NULL" to represent validity, as we do for the other special snapshots in snapmgr.c. And improve some obsolete comments. No regression test because I don't know a deterministic way to cause this failure. But the stress test shown in the original discussion provokes "cache lookup failed for relation 1255" within a few dozen seconds for me. Back-patch to 9.4 where MVCC catalog scans were introduced. (Note: it's quite easy to produce similar failures with the same test case in branches before 9.4. But MVCC catalog scans were supposed to fix that.) Discussion: <16447.1478818294@sss.pgh.pa.us>		9 years ago
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backend	Account for catalog snapshot in PGXACT->xmin updates.	9 years ago
bin	Change qr/foo$/m to qr/foo\n/m, for Perl 5.8.8.	9 years ago
common	…
fe_utils	Fix assorted places in psql to print version numbers >= 10 in new style.	10 years ago
include	Account for catalog snapshot in PGXACT->xmin updates.	9 years ago
interfaces	Stamp 9.6.1.	9 years ago
makefiles	…
pl	Rationalize and document pltcl's handling of magic ".tupno" array element.	9 years ago
port	Stamp 9.6.1.	9 years ago
template	…
test	Change qr/foo$/m to qr/foo\n/m, for Perl 5.8.8.	9 years ago
timezone	More zic cleanup.	9 years ago
tools	Change qr/foo$/m to qr/foo\n/m, for Perl 5.8.8.	9 years ago
tutorial	…
.gitignore	…
DEVELOPERS	…
Makefile	Install TAP test infrastructure so it's available for extension testing.	9 years ago
Makefile.global.in	Make TAP test suites to work, when @INC does not contain current dir.	9 years ago
Makefile.shlib	Fix misstatement in comment in Makefile.shlib.	9 years ago
bcc32.mak	…
nls-global.mk	…
win32.mak	…