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Handle impending sinval queue overflow by means of a separate signal

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(SIGUSR1, which we have not been using recently) instead of piggybacking
on SIGUSR2-driven NOTIFY processing.  This has several good results:
the processing needed to drain the sinval queue is a lot less than the
processing needed to answer a NOTIFY; there's less contention since we
don't have a bunch of backends all trying to acquire exclusive lock on
pg_listener; backends that are sitting inside a transaction block can
still drain the queue, whereas NOTIFY processing can't run if there's
an open transaction block.  (This last is a fairly serious issue that
I don't think we ever recognized before --- with clients like JDBC that
tend to sit with open transaction blocks, the sinval queue draining
mechanism never really worked as intended, probably resulting in a lot
of useless cache-reset overhead.)  This is the last of several proposed
changes in response to Philip Warner's recent report of sinval-induced
performance problems.
This commit is contained in:
Tom Lane
2004-05-23 03:50:45 +00:00
parent 4d86ae4260
commit ebfc56d3fb
8 changed files with 289 additions and 37 deletions
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15
src/include/storage/sinval.h
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@@ -7,7 +7,7 @@
* Portions Copyright (c) 1996-2003, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* $PostgreSQL: pgsql/src/include/storage/sinval.h,v 1.33 2004/02/10 01:55:26 tgl Exp $
* $PostgreSQL: pgsql/src/include/storage/sinval.h,v 1.34 2004/05/23 03:50:45 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -99,10 +99,19 @@ extern bool DatabaseHasActiveBackends(Oid databaseId, bool ignoreMyself);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestXmin(bool allDbs);
extern int CountActiveBackends(void);
extern int CountEmptyBackendSlots(void);
/* Use "struct PGPROC", not PGPROC, to avoid including proc.h here */
extern struct PGPROC *BackendIdGetProc(BackendId procId);
extern int CountEmptyBackendSlots(void);
/* signal handler for catchup events (SIGUSR1) */
extern void CatchupInterruptHandler(SIGNAL_ARGS);
/*
* enable/disable processing of catchup events directly from signal handler.
* The enable routine first performs processing of any catchup events that
* have occurred since the last disable.
*/
extern void EnableCatchupInterrupt(void);
extern bool DisableCatchupInterrupt(void);
#endif /* SINVAL_H */