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Andres Freund 5c8dabecdb Reconsider when to wait for WAL flushes/syncrep during commit. ... Up to now RecordTransactionCommit() waited for WAL to be flushed (if synchronous_commit != off) and to be synchronously replicated (if enabled), even if a transaction did not have a xid assigned. The primary reason for that is that sequence's nextval() did not assign a xid, but are worthwhile to wait for on commit. This can be problematic because sometimes read only transactions do write WAL, e.g. HOT page prune records. That then could lead to read only transactions having to wait during commit. Not something people expect in a read only transaction. This lead to such strange symptoms as backends being seemingly stuck during connection establishment when all synchronous replicas are down. Especially annoying when said stuck connection is the standby trying to reconnect to allow syncrep again... This behavior also is involved in a rather complicated <= 9.4 bug where the transaction started by catchup interrupt processing waited for syncrep using latches, but didn't get the wakeup because it was already running inside the same overloaded signal handler. Fix the issue here doesn't properly solve that issue, merely papers over the problems. In 9.5 catchup interrupts aren't processed out of signal handlers anymore. To fix all this, make nextval() acquire a top level xid, and only wait for transaction commit if a transaction both acquired a xid and emitted WAL records. If only a xid has been assigned we don't uselessly want to wait just because of writes to temporary/unlogged tables; if only WAL has been written we don't want to wait just because of HOT prunes. The xid assignment in nextval() is unlikely to cause overhead in real-world workloads. For one it only happens SEQ_LOG_VALS/32 values anyway, for another only usage of nextval() without using the result in an insert or similar is affected. Discussion: 20150223165359.GF30784@awork2.anarazel.de, 369698E947874884A77849D8FE3680C2@maumau, 5CF4ABBA67674088B3941894E22A0D25@maumau Per complaint from maumau and Thom Brown Backpatch all the way back; 9.0 doesn't have syncrep, but it seems better to be consistent behavior across all maintained branches.		11 years ago
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common	Remove tabs after spaces in C comments	12 years ago
gin	Fix bug where GIN scan keys were not initialized with gin_fuzzy_search_limit.	11 years ago
gist	Cannot rely on %z printf length modifier.	11 years ago
hash	Fix race condition between hot standby and restoring a full-page image.	11 years ago
heap	Fix race condition between hot standby and restoring a full-page image.	11 years ago
index	Fix BuildIndexValueDescription for expressions	11 years ago
nbtree	Fix column-privilege leak in error-message paths	11 years ago
transam	Reconsider when to wait for WAL flushes/syncrep during commit.	11 years ago
Makefile	Remove cvs keywords from all files.	16 years ago