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Commitfad153e

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Rewrite the sinval messaging mechanism to reduce contention and avoid
unnecessary cache resets. The major changes are:* When the queue overflows, we only issue a cache reset to the specificbackend or backends that still haven't read the oldest message, ratherthan resetting everyone as in the original coding.* When we observe backend(s) falling well behind, we signal SIGUSR1to only one backend, the one that is furthest behind and doesn't alreadyhave a signal outstanding for it. When it finishes catching up, it willin turn signal SIGUSR1 to the next-furthest-back guy, if there is one thatis far enough behind to justify a signal. The PMSIGNAL_WAKEN_CHILDRENmechanism is removed.* We don't attempt to clean out dead messages after every message-receiptoperation; rather, we do it on the insertion side, and only when the queuefullness passes certain thresholds.* Split SInvalLock into SInvalReadLock and SInvalWriteLock so that readersdon't block writers nor vice versa (except during the infrequent queuecleanout operations).* Transfer multiple sinval messages for each acquisition of a read orwrite lock.
1 parent30dc388 commitfad153e

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8 files changed

+413
-244
lines changed

8 files changed

+413
-244
lines changed

‎src/backend/postmaster/postmaster.c‎

Lines changed: 1 addition & 11 deletions
Original file line numberDiff line numberDiff line change
@@ -37,7 +37,7 @@
3737
*
3838
*
3939
* IDENTIFICATION
40-
* $PostgreSQL: pgsql/src/backend/postmaster/postmaster.c,v 1.558 2008/06/06 22:35:22 alvherre Exp $
40+
* $PostgreSQL: pgsql/src/backend/postmaster/postmaster.c,v 1.559 2008/06/19 21:32:56 tgl Exp $
4141
*
4242
* NOTES
4343
*
@@ -3829,16 +3829,6 @@ sigusr1_handler(SIGNAL_ARGS)
38293829
load_role();
38303830
}
38313831

3832-
if (CheckPostmasterSignal(PMSIGNAL_WAKEN_CHILDREN))
3833-
{
3834-
/*
3835-
* Send SIGUSR1 to all children (triggers CatchupInterruptHandler).
3836-
* See storage/ipc/sinval[adt].c for the use of this.
3837-
*/
3838-
if (Shutdown <=SmartShutdown)
3839-
SignalChildren(SIGUSR1);
3840-
}
3841-
38423832
if (CheckPostmasterSignal(PMSIGNAL_WAKEN_ARCHIVER)&&
38433833
PgArchPID!=0)
38443834
{

‎src/backend/storage/ipc/sinval.c‎

Lines changed: 69 additions & 37 deletions
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
88
*
99
*
1010
* IDENTIFICATION
11-
* $PostgreSQL: pgsql/src/backend/storage/ipc/sinval.c,v 1.85 2008/03/17 11:50:26 alvherre Exp $
11+
* $PostgreSQL: pgsql/src/backend/storage/ipc/sinval.c,v 1.86 2008/06/19 21:32:56 tgl Exp $
1212
*
1313
*-------------------------------------------------------------------------
1414
*/
@@ -17,19 +17,17 @@
1717
#include"access/xact.h"
1818
#include"commands/async.h"
1919
#include"miscadmin.h"
20-
#include"storage/backendid.h"
2120
#include"storage/ipc.h"
22-
#include"storage/proc.h"
2321
#include"storage/sinvaladt.h"
2422
#include"utils/inval.h"
2523

2624

2725
/*
2826
* Because backends sitting idle will not be reading sinval events, we
2927
* need a way to give an idle backend a swift kick in the rear and make
30-
* it catch up before the sinval queue overflows and forceseveryone
31-
* through a cache reset exercise.This is done bybroadcasting SIGUSR1
32-
* toall backends when the queue is threatening to become full.
28+
* it catch up before the sinval queue overflows and forcesit to go
29+
* through a cache reset exercise.This is done bysending SIGUSR1
30+
* toany backend that gets too far behind.
3331
*
3432
* State for catchup events consists of two flags: one saying whether
3533
* the signal handler is currently allowed to call ProcessCatchupEvent
@@ -47,67 +45,101 @@ static void ProcessCatchupEvent(void);
4745

4846

4947
/*
50-
*SendSharedInvalidMessage
51-
*Addashared-cache-invalidation message to the global SI message queue.
48+
*SendSharedInvalidMessages
49+
*Add shared-cache-invalidation message(s) to the global SI message queue.
5250
*/
5351
void
54-
SendSharedInvalidMessage(SharedInvalidationMessage*msg)
52+
SendSharedInvalidMessages(constSharedInvalidationMessage*msgs,intn)
5553
{
56-
boolinsertOK;
57-
58-
insertOK=SIInsertDataEntry(msg);
59-
if (!insertOK)
60-
elog(DEBUG4,"SI buffer overflow");
54+
SIInsertDataEntries(msgs,n);
6155
}
6256

6357
/*
6458
* ReceiveSharedInvalidMessages
6559
*Process shared-cache-invalidation messages waiting for this backend
6660
*
61+
* We guarantee to process all messages that had been queued before the
62+
* routine was entered. It is of course possible for more messages to get
63+
* queued right after our last SIGetDataEntries call.
64+
*
6765
* NOTE: it is entirely possible for this routine to be invoked recursively
6866
* as a consequence of processing inside the invalFunction or resetFunction.
69-
* Hence, we must be holding no SI resources when we call them. The only
70-
* bad side-effect is that SIDelExpiredDataEntries might be called extra
71-
* times on the way out of a nested call.
67+
* Furthermore, such a recursive call must guarantee that all outstanding
68+
* inval messages have been processed before it exits. This is the reason
69+
* for the strange-looking choice to use a statically allocated buffer array
70+
* and counters; it's so that a recursive call can process messages already
71+
* sucked out of sinvaladt.c.
7272
*/
7373
void
7474
ReceiveSharedInvalidMessages(
7575
void (*invalFunction) (SharedInvalidationMessage*msg),
7676
void (*resetFunction) (void))
7777
{
78-
SharedInvalidationMessagedata;
79-
intgetResult;
80-
boolgotMessage= false;
78+
#defineMAXINVALMSGS 32
79+
staticSharedInvalidationMessagemessages[MAXINVALMSGS];
80+
/*
81+
* We use volatile here to prevent bugs if a compiler doesn't realize
82+
* that recursion is a possibility ...
83+
*/
84+
staticvolatileintnextmsg=0;
85+
staticvolatileintnummsgs=0;
8186

82-
for (;;)
87+
/* Deal with any messages still pending from an outer recursion */
88+
while (nextmsg<nummsgs)
8389
{
84-
/*
85-
* We can discard any pending catchup event, since we will not exit
86-
* this loop until we're fully caught up.
87-
*/
88-
catchupInterruptOccurred=0;
90+
SharedInvalidationMessage*msg=&messages[nextmsg++];
8991

90-
getResult=SIGetDataEntry(MyBackendId,&data);
92+
invalFunction(msg);
93+
}
94+
95+
do
96+
{
97+
intgetResult;
98+
99+
nextmsg=nummsgs=0;
100+
101+
/* Try to get some more messages */
102+
getResult=SIGetDataEntries(messages,MAXINVALMSGS);
91103

92-
if (getResult==0)
93-
break;/* nothing more to do */
94104
if (getResult<0)
95105
{
96106
/* got a reset message */
97107
elog(DEBUG4,"cache state reset");
98108
resetFunction();
109+
break;/* nothing more to do */
99110
}
100-
else
111+
112+
/* Process them, being wary that a recursive call might eat some */
113+
nextmsg=0;
114+
nummsgs=getResult;
115+
116+
while (nextmsg<nummsgs)
101117
{
102-
/* got a normal data message */
103-
invalFunction(&data);
118+
SharedInvalidationMessage*msg=&messages[nextmsg++];
119+
120+
invalFunction(msg);
104121
}
105-
gotMessage= true;
106-
}
107122

108-
/* If we got any messages, try to release dead messages */
109-
if (gotMessage)
110-
SIDelExpiredDataEntries(false);
123+
/*
124+
* We only need to loop if the last SIGetDataEntries call (which
125+
* might have been within a recursive call) returned a full buffer.
126+
*/
127+
}while (nummsgs==MAXINVALMSGS);
128+
129+
/*
130+
* We are now caught up. If we received a catchup signal, reset that
131+
* flag, and call SICleanupQueue(). This is not so much because we
132+
* need to flush dead messages right now, as that we want to pass on
133+
* the catchup signal to the next slowest backend. "Daisy chaining" the
134+
* catchup signal this way avoids creating spikes in system load for
135+
* what should be just a background maintenance activity.
136+
*/
137+
if (catchupInterruptOccurred)
138+
{
139+
catchupInterruptOccurred=0;
140+
elog(DEBUG4,"sinval catchup complete, cleaning queue");
141+
SICleanupQueue(false,0);
142+
}
111143
}
112144

113145

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