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| author | Noah Misch <noah@leadboat.com> | 2020-08-15 10:15:53 -0700 |
|---|---|---|
| committer | Noah Misch <noah@leadboat.com> | 2020-08-15 10:15:56 -0700 |
| commit | 592a589a04bd456410b853d86bd05faa9432cbbb (patch) | |
| tree | b04dc452ff054c9281e8b1c16ed6f50145cee4d3 /src/backend/executor/nodeFunctionscan.c | |
| parent | b538e83f17e36fd0fe0686815da0ff5866ce8a64 (diff) | |
| download | postgresql-592a589a04bd456410b853d86bd05faa9432cbbb.tar.gz postgresql-592a589a04bd456410b853d86bd05faa9432cbbb.zip | |
Prevent concurrent SimpleLruTruncate() for any given SLRU.
The SimpleLruTruncate() header comment states the new coding rule. To
achieve this, add locktype "frozenid" and two LWLocks. This closes a
rare opportunity for data loss, which manifested as "apparent
wraparound" or "could not access status of transaction" errors. Data
loss is more likely in pg_multixact, due to released branches' thin
margin between multiStopLimit and multiWrapLimit. If a user's physical
replication primary logged ": apparent wraparound" messages, the user
should rebuild standbys of that primary regardless of symptoms. At less
risk is a cluster having emitted "not accepting commands" errors or
"must be vacuumed" warnings at some point. One can test a cluster for
this data loss by running VACUUM FREEZE in every database. Back-patch
to 9.5 (all supported versions).
Discussion: https://postgr.es/m/20190218073103.GA1434723@rfd.leadboat.com
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