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Rewrite the sinval messaging mechanism to reduce contention and avoid

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unnecessary cache resets.  The major changes are:

* When the queue overflows, we only issue a cache reset to the specific
backend or backends that still haven't read the oldest message, rather
than resetting everyone as in the original coding.

* When we observe backend(s) falling well behind, we signal SIGUSR1
to only one backend, the one that is furthest behind and doesn't already
have a signal outstanding for it.  When it finishes catching up, it will
in turn signal SIGUSR1 to the next-furthest-back guy, if there is one that
is far enough behind to justify a signal.  The PMSIGNAL_WAKEN_CHILDREN
mechanism is removed.

* We don't attempt to clean out dead messages after every message-receipt
operation; rather, we do it on the insertion side, and only when the queue
fullness passes certain thresholds.

* Split SInvalLock into SInvalReadLock and SInvalWriteLock so that readers
don't block writers nor vice versa (except during the infrequent queue
cleanout operations).

* Transfer multiple sinval messages for each acquisition of a read or
write lock.
This commit is contained in:
Tom Lane
2008-06-19 21:32:56 +00:00
parent 30dc388a0d
commit fad153ec45
8 changed files with 416 additions and 247 deletions
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14
src/include/storage/sinvaladt.h
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@@ -1,12 +1,13 @@
/*-------------------------------------------------------------------------
*
* sinvaladt.h
* POSTGRES shared cache invalidation segment definitions.
* POSTGRES shared cache invalidation data manager.
*
* The shared cache invalidation manager is responsible for transmitting
* invalidation messages between backends. Any message sent by any backend
* must be delivered to all already-running backends before it can be
* forgotten.
* forgotten. (If we run out of space, we instead deliver a "RESET"
* message to backends that have fallen too far behind.)
*
* The struct type SharedInvalidationMessage, defining the contents of
* a single message, is defined in sinval.h.
@@ -14,7 +15,7 @@
* Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* $PostgreSQL: pgsql/src/include/storage/sinvaladt.h,v 1.47 2008/03/17 11:50:27 alvherre Exp $
* $PostgreSQL: pgsql/src/include/storage/sinvaladt.h,v 1.48 2008/06/19 21:32:56 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -23,7 +24,6 @@
#include "storage/sinval.h"
/*
* prototypes for functions in sinvaladt.c
*/
@@ -31,9 +31,9 @@ extern Size SInvalShmemSize(void);
extern void CreateSharedInvalidationState(void);
extern void SharedInvalBackendInit(void);
extern bool SIInsertDataEntry(SharedInvalidationMessage *data);
extern int SIGetDataEntry(int backendId, SharedInvalidationMessage *data);
extern void SIDelExpiredDataEntries(bool locked);
extern void SIInsertDataEntries(const SharedInvalidationMessage *data, int n);
extern int SIGetDataEntries(SharedInvalidationMessage *data, int datasize);
extern void SICleanupQueue(bool callerHasWriteLock, int minFree);
extern LocalTransactionId GetNextLocalTransactionId(void);