Alvaro Herrera a5736bf754 Fix traversal of half-frozen update chains ... When some tuple versions in an update chain are frozen due to them being older than freeze_min_age, the xmax/xmin trail can become broken. This breaks HOT (and probably other things). A subsequent VACUUM can break things in more serious ways, such as leaving orphan heap-only tuples whose root HOT redirect items were removed. This can be seen because index creation (or REINDEX) complain like ERROR: XX000: failed to find parent tuple for heap-only tuple at (0,7) in table "t" Because of relfrozenxid contraints, we cannot avoid the freezing of the early tuples, so we must cope with the results: whenever we see an Xmin of FrozenTransactionId, consider it a match for whatever the previous Xmax value was. This problem seems to have appeared in 9.3 with multixact changes, though strictly speaking it seems unrelated. Since 9.4 we have commit 37484ad2a "Change the way we mark tuples as frozen", so the fix is simple: just compare the raw Xmin (still stored in the tuple header, since freezing merely set an infomask bit) to the Xmax. But in 9.3 we rewrite the Xmin value to FrozenTransactionId, so the original value is lost and we have nothing to compare the Xmax with. To cope with that case we need to compare the Xmin with FrozenXid, assume it's a match, and hope for the best. Sadly, since you can pg_upgrade a 9.3 instance containing half-frozen pages to newer releases, we need to keep the old check in newer versions too, which seems a bit brittle; I hope we can somehow get rid of that. I didn't optimize the new function for performance. The new coding is probably a bit slower than before, since there is a function call rather than a straight comparison, but I'd rather have it work correctly than be fast but wrong. This is a followup after 20b6552242 fixed a few related problems. Apparently, in 9.6 and up there are more ways to get into trouble, but in 9.3 - 9.5 I cannot reproduce a problem anymore with this patch, so there must be a separate bug. Reported-by: Peter Geoghegan Diagnosed-by: Peter Geoghegan, Michael Paquier, Daniel Wood, Yi Wen Wong, Álvaro Discussion: https://postgr.es/m/CAH2-Wznm4rCrhFAiwKPWTpEw2bXDtgROZK7jWWGucXeH3D1fmA@mail.gmail.com		2017-10-06 17:20:01 +02:00
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backend	Fix traversal of half-frozen update chains	2017-10-06 17:20:01 +02:00
bin	Replace most usages of ntoh[ls] and hton[sl] with pg_bswap.h.	2017-10-01 15:36:14 -07:00
common	Replace most usages of ntoh[ls] and hton[sl] with pg_bswap.h.	2017-10-01 15:36:14 -07:00
fe_utils	Provide a test for variable existence in psql	2017-09-21 19:02:23 -04:00
include	Fix traversal of half-frozen update chains	2017-10-06 17:20:01 +02:00
interfaces	Replace most usages of ntoh[ls] and hton[sl] with pg_bswap.h.	2017-10-01 15:36:14 -07:00
makefiles	Always use -fPIC, not -fpic, when building shared libraries with gcc.	2017-06-01 13:32:55 -04:00
pl	Use Py_RETURN_NONE where suitable	2017-09-29 16:51:39 -04:00
port	Yet another pg_bswap typo in a windows only file.	2017-10-01 20:05:27 -07:00
template	Remove "sco" and "unixware" ports.	2016-10-11 11:26:04 -04:00
test	Basic partition-wise join functionality.	2017-10-06 11:11:10 -04:00
timezone	Sync our copy of the timezone library with IANA tzcode master.	2017-09-22 00:04:29 -04:00
tools	Attempt to adapt windows build for 212e6f34d5.	2017-10-04 09:32:02 -07:00
tutorial	Distinguish selectivity of < from <= and > from >=.	2017-09-13 11:12:39 -04:00
.gitignore	Convert cvsignore to gitignore, and add .gitignore for build targets.	2010-09-22 12:57:04 +02:00
DEVELOPERS	Replace a couple of references to files that no longer exist in the source	2009-05-04 08:08:47 +00:00
Makefile	Remove redundant coverage target	2017-02-17 08:56:57 -05:00
Makefile.global.in	Add PostgreSQL version to coverage output	2017-09-29 08:54:47 -04:00
Makefile.shlib	Remove support for bcc and msvc standalone libpq builds	2017-04-11 15:22:21 +02:00
nls-global.mk	nls-global.mk: search build dir for source files, too	2016-06-07 18:55:18 -04:00