Movatterモバイル変換

[0]ホーム
URL:

Skip to content

Navigation Menu

Sign in
Appearance settings

Search code, repositories, users, issues, pull requests...

Provide feedback

We read every piece of feedback, and take your input very seriously.

Saved searches

Use saved searches to filter your results more quickly

 Sign up
Appearance settings

Commit6308ba0

Browse files
committed
Improve control logic for bgwriter hibernation mode.
Commit6d90eaa added a hibernation modeto the bgwriter to reduce the server's idle-power consumption. However,its interaction with the detailed behavior of BgBufferSync's feedbackcontrol loop wasn't very well thought out. That control loop dependsprimarily on the rate of buffer allocation, not the rate of bufferdirtying, so the hibernation mode has to be designed to operate only whenno new buffer allocations are happening. Also, the check for whether thesystem is effectively idle was not quite right and would fail to detecta constant low level of activity, thus allowing the bgwriter to go intohibernation mode in a way that would let the cycle time vary quite a bit,possibly further confusing the feedback loop. To fix, move the wakeupsupport from MarkBufferDirty and SetBufferCommitInfoNeedsSave intoStrategyGetBuffer, and prevent the bgwriter from entering hibernation modeunless no buffer allocations have happened recently.In addition, fix the delaying logic to remove the problem of possibly notresponding to signals promptly, which was basically caused by trying to usethe process latch's is_set flag for multiple purposes. I can't prove itbut I'm suspicious that that hack was responsible for the intermittent"postmaster does not shut down" failures we've been seeing in the buildfarmlately. In any case it did nothing to improve the readability orrobustness of the code.In passing, express the hibernation sleep time as a multiplier onBgWriterDelay, not a constant. I'm not sure whether there's any value inexposing the longer sleep time as an independently configurable setting,but we can at least make it act like this for little extra code.
1 parent668f959 commit6308ba0

File tree

7 files changed

+145
-169
lines changed

7 files changed

+145
-169
lines changed

‎src/backend/postmaster/bgwriter.c‎

Lines changed: 64 additions & 132 deletions
Original file line numberDiff line numberDiff line change
@@ -21,10 +21,7 @@
2121
*
2222
* If the bgwriter exits unexpectedly, the postmaster treats that the same
2323
* as a backend crash: shared memory may be corrupted, so remaining backends
24-
* should be killed by SIGQUIT and then a recovery cycle started. (Even if
25-
* shared memory isn't corrupted, we have lost information about which
26-
* files need to be fsync'd for the next checkpoint, and so a system
27-
* restart needs to be forced.)
24+
* should be killed by SIGQUIT and then a recovery cycle started.
2825
*
2926
*
3027
* Portions Copyright (c) 1996-2012, PostgreSQL Global Development Group
@@ -48,6 +45,7 @@
4845
#include"pgstat.h"
4946
#include"postmaster/bgwriter.h"
5047
#include"storage/bufmgr.h"
48+
#include"storage/buf_internals.h"
5149
#include"storage/ipc.h"
5250
#include"storage/lwlock.h"
5351
#include"storage/pmsignal.h"
@@ -66,9 +64,10 @@
6664
intBgWriterDelay=200;
6765

6866
/*
69-
* Time to sleep between bgwriter rounds, when it has no work to do.
67+
* Multiplier to apply to BgWriterDelay when we decide to hibernate.
68+
* (Perhaps this needs to be configurable?)
7069
*/
71-
#defineBGWRITER_HIBERNATE_MS10000
70+
#defineHIBERNATE_FACTOR50
7271

7372
/*
7473
* Flags set by interrupt handlers for later service in the main loop.
@@ -81,10 +80,6 @@ static volatile sig_atomic_t shutdown_requested = false;
8180
*/
8281
staticboolam_bg_writer= false;
8382

84-
/* Prototypes for private functions */
85-
86-
staticvoidBgWriterNap(boolhibernating);
87-
8883
/* Signal handlers */
8984

9085
staticvoidbg_quickdie(SIGNAL_ARGS);
@@ -104,7 +99,7 @@ BackgroundWriterMain(void)
10499
{
105100
sigjmp_buflocal_sigjmp_buf;
106101
MemoryContextbgwriter_context;
107-
boolhibernating;
102+
boolprev_hibernate;
108103

109104
am_bg_writer= true;
110105

@@ -126,7 +121,7 @@ BackgroundWriterMain(void)
126121
* handler is still needed for latch wakeups.
127122
*/
128123
pqsignal(SIGHUP,BgSigHupHandler);/* set flag to read config file */
129-
pqsignal(SIGINT,SIG_IGN);/* as of 9.2 no longer requests checkpoint */
124+
pqsignal(SIGINT,SIG_IGN);
130125
pqsignal(SIGTERM,ReqShutdownHandler);/* shutdown */
131126
pqsignal(SIGQUIT,bg_quickdie);/* hard crash time */
132127
pqsignal(SIGALRM,SIG_IGN);
@@ -146,12 +141,6 @@ BackgroundWriterMain(void)
146141
/* We allow SIGQUIT (quickdie) at all times */
147142
sigdelset(&BlockSig,SIGQUIT);
148143

149-
/*
150-
* Advertise our latch that backends can use to wake us up while we're
151-
* sleeping.
152-
*/
153-
ProcGlobal->bgwriterLatch=&MyProc->procLatch;
154-
155144
/*
156145
* Create a resource owner to keep track of our resources (currently only
157146
* buffer pins).
@@ -246,26 +235,26 @@ BackgroundWriterMain(void)
246235
if (RecoveryInProgress())
247236
ThisTimeLineID=GetRecoveryTargetTLI();
248237

238+
/*
239+
* Reset hibernation state after any error.
240+
*/
241+
prev_hibernate= false;
242+
249243
/*
250244
* Loop forever
251245
*/
252-
hibernating= false;
253246
for (;;)
254247
{
255-
boollapped;
248+
boolcan_hibernate;
249+
intrc;
256250

257-
/*
258-
* Emergency bailout if postmaster has died. This is to avoid the
259-
* necessity for manual cleanup of all postmaster children.
260-
*/
261-
if (!PostmasterIsAlive())
262-
exit(1);
251+
/* Clear any already-pending wakeups */
252+
ResetLatch(&MyProc->procLatch);
263253

264254
if (got_SIGHUP)
265255
{
266256
got_SIGHUP= false;
267257
ProcessConfigFile(PGC_SIGHUP);
268-
/* update global shmem state for sync rep */
269258
}
270259
if (shutdown_requested)
271260
{
@@ -281,126 +270,69 @@ BackgroundWriterMain(void)
281270
/*
282271
* Do one cycle of dirty-buffer writing.
283272
*/
284-
if (hibernating&&bgwriter_lru_maxpages>0)
285-
ResetLatch(&MyProc->procLatch);
286-
lapped=BgBufferSync();
287-
288-
if (lapped&& !hibernating)
289-
{
290-
/*
291-
* BgBufferSync did nothing. Since there doesn't seem to be any
292-
* work for the bgwriter to do, go into slower-paced
293-
* "hibernation" mode, where we sleep for much longer times than
294-
* bgwriter_delay says. Fewer wakeups saves electricity. If a
295-
* backend starts dirtying pages again, it will wake us up by
296-
* setting our latch.
297-
*
298-
* The latch is kept set during productive cycles where buffers
299-
* are written, and only reset before going into a longer sleep.
300-
* That ensures that when there's a constant trickle of activity,
301-
* the SetLatch() calls that backends have to do will see the
302-
* latch as already set, and are not slowed down by having to
303-
* actually set the latch and signal us.
304-
*/
305-
hibernating= true;
306-
307-
/*
308-
* Take one more short nap and perform one more bgwriter cycle -
309-
* someone might've dirtied a buffer just after we finished the
310-
* previous bgwriter cycle, while the latch was still set. If
311-
* we still find nothing to do after this cycle, the next sleep
312-
* will be longer.
313-
*/
314-
BgWriterNap(false);
315-
continue;
316-
}
317-
elseif (!lapped&&hibernating)
318-
{
319-
/*
320-
* Woken up from hibernation. Set the latch just in case it's
321-
* not set yet (usually we wake up from hibernation because a
322-
* backend already set the latch, but not necessarily).
323-
*/
324-
SetLatch(&MyProc->procLatch);
325-
hibernating= false;
326-
}
273+
can_hibernate=BgBufferSync();
327274

328275
/*
329-
* Take a short or long nap, depending on whether there was any work
330-
* to do.
276+
* Send off activity statistics to the stats collector
331277
*/
332-
BgWriterNap(hibernating);
333-
}
334-
}
278+
pgstat_send_bgwriter();
335279

336-
/*
337-
* BgWriterNap -- Nap for the configured time or until a signal is received.
338-
*
339-
* If 'hibernating' is false, sleeps for bgwriter_delay milliseconds.
340-
* Otherwise sleeps longer, but also wakes up if the process latch is set.
341-
*/
342-
staticvoid
343-
BgWriterNap(boolhibernating)
344-
{
345-
longudelay;
346-
347-
/*
348-
* Send off activity statistics to the stats collector
349-
*/
350-
pgstat_send_bgwriter();
351-
352-
/*
353-
* If there was no work to do in the previous bgwriter cycle, take a
354-
* longer nap.
355-
*/
356-
if (hibernating)
357-
{
358280
/*
359-
* We wake on a buffer being dirtied. It's possible that some
360-
* useful work will become available for the bgwriter to do without
361-
* a buffer actually being dirtied, like when a dirty buffer's usage
362-
* count is decremented to zero or it's unpinned. This corner case
363-
* is judged as too marginal to justify adding additional SetLatch()
364-
* calls in very hot code paths, cheap though those calls may be.
281+
* Sleep until we are signaled or BgWriterDelay has elapsed.
365282
*
366-
* We still wake up periodically, so that BufferAlloc stats are
367-
* updated reasonably promptly.
283+
* Note: the feedback control loop in BgBufferSync() expects that we
284+
* will call it every BgWriterDelay msec. While it's not critical for
285+
* correctness that that be exact, the feedback loop might misbehave
286+
* if we stray too far from that. Hence, avoid loading this process
287+
* down with latch events that are likely to happen frequently during
288+
* normal operation.
368289
*/
369-
intres=WaitLatch(&MyProc->procLatch,
370-
WL_LATCH_SET |WL_TIMEOUT |WL_POSTMASTER_DEATH,
371-
BGWRITER_HIBERNATE_MS);
290+
rc=WaitLatch(&MyProc->procLatch,
291+
WL_LATCH_SET |WL_TIMEOUT |WL_POSTMASTER_DEATH,
292+
BgWriterDelay/* ms */);
372293

373294
/*
374-
* Only do a quick return if timeout was reached (or postmaster died)
375-
* to ensure that no less than BgWriterDelay ms has passed between
376-
* BgBufferSyncs - WaitLatch() might have returned instantaneously.
295+
* If no latch event and BgBufferSync says nothing's happening, extend
296+
* the sleep in "hibernation" mode, where we sleep for much longer
297+
* than bgwriter_delay says. Fewer wakeups save electricity. When a
298+
* backend starts using buffers again, it will wake us up by setting
299+
* our latch. Because the extra sleep will persist only as long as no
300+
* buffer allocations happen, this should not distort the behavior of
301+
* BgBufferSync's control loop too badly; essentially, it will think
302+
* that the system-wide idle interval didn't exist.
303+
*
304+
* There is a race condition here, in that a backend might allocate a
305+
* buffer between the time BgBufferSync saw the alloc count as zero
306+
* and the time we call StrategyNotifyBgWriter. While it's not
307+
* critical that we not hibernate anyway, we try to reduce the odds of
308+
* that by only hibernating when BgBufferSync says nothing's happening
309+
* for two consecutive cycles. Also, we mitigate any possible
310+
* consequences of a missed wakeup by not hibernating forever.
377311
*/
378-
if (res& (WL_TIMEOUT |WL_POSTMASTER_DEATH))
379-
return;
380-
}
312+
if (rc==WL_TIMEOUT&&can_hibernate&&prev_hibernate)
313+
{
314+
/* Ask for notification at next buffer allocation */
315+
StrategyNotifyBgWriter(&MyProc->procLatch);
316+
/* Sleep ... */
317+
rc=WaitLatch(&MyProc->procLatch,
318+
WL_LATCH_SET |WL_TIMEOUT |WL_POSTMASTER_DEATH,
319+
BgWriterDelay*HIBERNATE_FACTOR);
320+
/* Reset the notification request in case we timed out */
321+
StrategyNotifyBgWriter(NULL);
322+
}
381323

382-
/*
383-
* Nap for the configured time.
384-
*
385-
* On some platforms, signals won't interrupt the sleep. To ensure we
386-
* respond reasonably promptly when someone signals us, break down the
387-
* sleep into 1-second increments, and check for interrupts after each
388-
* nap.
389-
*/
390-
udelay=BgWriterDelay*1000L;
324+
/*
325+
* Emergency bailout if postmaster has died. This is to avoid the
326+
* necessity for manual cleanup of all postmaster children.
327+
*/
328+
if (rc&WL_POSTMASTER_DEATH)
329+
exit(1);
391330

392-
while (udelay>999999L)
393-
{
394-
if (got_SIGHUP||shutdown_requested)
395-
break;
396-
pg_usleep(1000000L);
397-
udelay-=1000000L;
331+
prev_hibernate=can_hibernate;
398332
}
399-
400-
if (!(got_SIGHUP||shutdown_requested))
401-
pg_usleep(udelay);
402333
}
403334

335+
404336
/* --------------------------------
405337
*signal handler routines
406338
* --------------------------------

0 commit comments

Comments
 (0)
[8]ページ先頭
©2009-2025 Movatter.jp