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Commitfa0e03c

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Remove InitXLOGAccess().
It's not great that RecoveryInProgress() calls InitXLOGAccess(),because a status inquiry function typically shouldn't have the sideeffect of performing initializations. We could fix that by callingInitXLOGAccess() from some other place, but instead, let's remove italtogether.One thing InitXLogAccess() did is initialize wal_segment_size, but itdoesn't need to do that. In the postmaster, PostmasterMain() callsLocalProcessControlFile(), and all child processes will inherit thatvalue -- except in EXEC_BACKEND bulds, but then each backend runsSubPostmasterMain() which also calls LocalProcessControlFile().The other thing InitXLOGAccess() did is update RedoRecPtr anddoPageWrites, but that's not critical, because all code that usesthem will just retry if it turns out that they've changed. Theonly difference is that most code will now see an initial value thatis definitely invalid instead of one that might have just been wayout of date, but that will only happen once per backend lifetime,so it shouldn't be a big deal.Patch by me, reviewed by Nathan Bossart, Michael Paquier, AndresFreund, Heikki Linnakangas, and Álvaro Herrera.Discussion:http://postgr.es/m/CA+TgmoY7b65qRjzHN_tWUk8B4sJqk1vj1d31uepVzmgPnZKeLg@mail.gmail.com
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4 files changed

+22
-64
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4 files changed

+22
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lines changed

‎src/backend/access/transam/xlog.c‎

Lines changed: 17 additions & 46 deletions
Original file line numberDiff line numberDiff line change
@@ -350,15 +350,27 @@ XLogRecPtrXactLastCommitEnd = InvalidXLogRecPtr;
350350
* XLogCtl->Insert.RedoRecPtr, whenever we can safely do so (ie, when we
351351
* hold an insertion lock). See XLogInsertRecord for details. We are also
352352
* allowed to update from XLogCtl->RedoRecPtr if we hold the info_lck;
353-
* see GetRedoRecPtr. A freshly spawned backend obtains the value during
354-
* InitXLOGAccess.
353+
* see GetRedoRecPtr.
354+
*
355+
* NB: Code that uses this variable must be prepared not only for the
356+
* possibility that it may be arbitrarily out of date, but also for the
357+
* possibility that it might be set to InvalidXLogRecPtr. We used to
358+
* initialize it as a side effect of the first call to RecoveryInProgress(),
359+
* which meant that most code that might use it could assume that it had a
360+
* real if perhaps stale value. That's no longer the case.
355361
*/
356362
staticXLogRecPtrRedoRecPtr;
357363

358364
/*
359365
* doPageWrites is this backend's local copy of (forcePageWrites ||
360366
* fullPageWrites). It is used together with RedoRecPtr to decide whether
361367
* a full-page image of a page need to be taken.
368+
*
369+
* NB: Initially this is false, and there's no guarantee that it will be
370+
* initialized to any other value before it is first used. Any code that
371+
* makes use of it must recheck the value after obtaining a WALInsertLock,
372+
* and respond appropriately if it turns out that the previous value wasn't
373+
* accurate.
362374
*/
363375
staticbooldoPageWrites;
364376

@@ -8390,9 +8402,6 @@ PerformRecoveryXLogAction(void)
83908402
*
83918403
* Unlike testing InRecovery, this works in any process that's connected to
83928404
* shared memory.
8393-
*
8394-
* As a side-effect, we initialize the local RedoRecPtr variable the first
8395-
* time we see that recovery is finished.
83968405
*/
83978406
bool
83988407
RecoveryInProgress(void)
@@ -8414,23 +8423,6 @@ RecoveryInProgress(void)
84148423

84158424
LocalRecoveryInProgress= (xlogctl->SharedRecoveryState!=RECOVERY_STATE_DONE);
84168425

8417-
/*
8418-
* Initialize TimeLineID and RedoRecPtr when we discover that recovery
8419-
* is finished. InitPostgres() relies upon this behaviour to ensure
8420-
* that InitXLOGAccess() is called at backend startup. (If you change
8421-
* this, see also LocalSetXLogInsertAllowed.)
8422-
*/
8423-
if (!LocalRecoveryInProgress)
8424-
{
8425-
/*
8426-
* If we just exited recovery, make sure we read TimeLineID and
8427-
* RedoRecPtr after SharedRecoveryState (for machines with weak
8428-
* memory ordering).
8429-
*/
8430-
pg_memory_barrier();
8431-
InitXLOGAccess();
8432-
}
8433-
84348426
/*
84358427
* Note: We don't need a memory barrier when we're still in recovery.
84368428
* We might exit recovery immediately after return, so the caller
@@ -8547,9 +8539,6 @@ LocalSetXLogInsertAllowed(void)
85478539

85488540
LocalXLogInsertAllowed=1;
85498541

8550-
/* Initialize as RecoveryInProgress() would do when switching state */
8551-
InitXLOGAccess();
8552-
85538542
returnoldXLogAllowed;
85548543
}
85558544

@@ -8656,25 +8645,6 @@ ReadCheckpointRecord(XLogReaderState *xlogreader, XLogRecPtr RecPtr,
86568645
returnrecord;
86578646
}
86588647

8659-
/*
8660-
* This must be called in a backend process before creating WAL records
8661-
* (except in a standalone backend, which does StartupXLOG instead). We need
8662-
* to initialize the local copy of RedoRecPtr.
8663-
*/
8664-
void
8665-
InitXLOGAccess(void)
8666-
{
8667-
XLogCtlInsert*Insert=&XLogCtl->Insert;
8668-
8669-
/* set wal_segment_size */
8670-
wal_segment_size=ControlFile->xlog_seg_size;
8671-
8672-
/* Use GetRedoRecPtr to copy the RedoRecPtr safely */
8673-
(void)GetRedoRecPtr();
8674-
/* Also update our copy of doPageWrites. */
8675-
doPageWrites= (Insert->fullPageWrites||Insert->forcePageWrites);
8676-
}
8677-
86788648
/*
86798649
* Return the current Redo pointer from shared memory.
86808650
*
@@ -8706,8 +8676,9 @@ GetRedoRecPtr(void)
87068676
* full-page image to be included in the WAL record.
87078677
*
87088678
* The returned values are cached copies from backend-private memory, and
8709-
* possibly out-of-date. XLogInsertRecord will re-check them against
8710-
* up-to-date values, while holding the WAL insert lock.
8679+
* possibly out-of-date or, indeed, uninitalized, in which case they will
8680+
* be InvalidXLogRecPtr and false, respectively. XLogInsertRecord will
8681+
* re-check them against up-to-date values, while holding the WAL insert lock.
87118682
*/
87128683
void
87138684
GetFullPageWriteInfo(XLogRecPtr*RedoRecPtr_p,bool*doPageWrites_p)

‎src/backend/postmaster/auxprocess.c‎

Lines changed: 0 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -154,7 +154,6 @@ AuxiliaryProcessMain(AuxProcType auxtype)
154154
proc_exit(1);
155155

156156
caseWalWriterProcess:
157-
InitXLOGAccess();
158157
WalWriterMain();
159158
proc_exit(1);
160159

‎src/backend/utils/init/postinit.c‎

Lines changed: 5 additions & 16 deletions
Original file line numberDiff line numberDiff line change
@@ -624,25 +624,14 @@ InitPostgres(const char *in_dbname, Oid dboid, const char *username,
624624
}
625625

626626
/*
627-
* Initialize local process's access to XLOG.
627+
* If this is either a bootstrap process nor a standalone backend, start
628+
* up the XLOG machinery, and register to have it closed down at exit.
629+
* In other cases, the startup process is responsible for starting up
630+
* the XLOG machinery, and the checkpointer for closing it down.
628631
*/
629-
if (IsUnderPostmaster)
630-
{
631-
/*
632-
* The postmaster already started the XLOG machinery, but we need to
633-
* call InitXLOGAccess(), if the system isn't in hot-standby mode.
634-
* This is handled by calling RecoveryInProgress and ignoring the
635-
* result.
636-
*/
637-
(void)RecoveryInProgress();
638-
}
639-
else
632+
if (!IsUnderPostmaster)
640633
{
641634
/*
642-
* We are either a bootstrap process or a standalone backend. Either
643-
* way, start up the XLOG machinery, and register to have it closed
644-
* down at exit.
645-
*
646635
* We don't yet have an aux-process resource owner, but StartupXLOG
647636
* and ShutdownXLOG will need one. Hence, create said resource owner
648637
* (and register a callback to clean it up after ShutdownXLOG runs).

‎src/include/access/xlog.h‎

Lines changed: 0 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -299,7 +299,6 @@ extern void BootStrapXLOG(void);
299299
externvoidLocalProcessControlFile(boolreset);
300300
externvoidStartupXLOG(void);
301301
externvoidShutdownXLOG(intcode,Datumarg);
302-
externvoidInitXLOGAccess(void);
303302
externvoidCreateCheckPoint(intflags);
304303
externboolCreateRestartPoint(intflags);
305304
externWALAvailabilityGetWALAvailability(XLogRecPtrtargetLSN);

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