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Hot Standby feedback for avoidance of cleanup conflicts on standby.

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Standby optionally sends back information about oldestXmin of queries
which is then checked and applied to the WALSender's proc->xmin.
GetOldestXmin() is modified slightly to agree with GetSnapshotData(),
so that all backends on primary include WALSender within their snapshots.
Note this does nothing to change the snapshot xmin on either master or
standby. Feedback piggybacks on the standby reply message.
vacuum_defer_cleanup_age is no longer used on standby, though parameter
still exists on primary, since some use cases still exist.

Simon Riggs, review comments from Fujii Masao, Heikki Linnakangas, Robert Haas
This commit is contained in:
Simon Riggs
2011-02-16 19:29:37 +00:00
parent 65076269ea
commit bca8b7f16a
11 changed files with 245 additions and 50 deletions
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src/backend/utils/misc/postgresql.conf.sample
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@ -196,6 +196,7 @@
#hot_standby = off # "on" allows queries during recovery
# (change requires restart)
#hot_standby_feedback = off # info from standby to prevent query conflicts
#max_standby_archive_delay = 30s # max delay before canceling queries
# when reading WAL from archive;
# -1 allows indefinite delay