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Commit6eba5a7

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Change pg_last_xlog_receive_location() not to move backwards. That makes
it a lot more useful for determining which standby is most up-to-date,for example. There was long discussions on whether overwriting existingexisting WAL makes sense to begin with, and whether we should do some moreextensive variable renaming, but this change nevertheless seems quiteuncontroversial.Fujii Masao, reviewed by Jeff Janes, Robert Haas, Stephen Frost.
1 parent47ad791 commit6eba5a7

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4 files changed

+29
-13
lines changed

4 files changed

+29
-13
lines changed

‎doc/src/sgml/func.sgml

Lines changed: 2 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -14179,10 +14179,8 @@ postgres=# SELECT * FROM pg_xlogfile_name_offset(pg_stop_backup());
1417914179
<entry><type>text</type></entry>
1418014180
<entry>Get last transaction log location received and synced to disk by
1418114181
streaming replication. While streaming replication is in progress
14182-
this will increase monotonically. But when streaming replication is
14183-
restarted this will back off to the replication starting position,
14184-
typically the beginning of the WAL file containing the current
14185-
replay location. If recovery has completed this will remain static at
14182+
this will increase monotonically. If recovery has completed this will
14183+
remain static at
1418614184
the value of the last WAL record received and synced to disk during
1418714185
recovery. If streaming replication is disabled, or if it has not yet
1418814186
started, the function returns NULL.

‎src/backend/replication/walreceiver.c

Lines changed: 6 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -218,7 +218,7 @@ WalReceiverMain(void)
218218

219219
/* Fetch information required to start streaming */
220220
strlcpy(conninfo, (char*)walrcv->conninfo,MAXCONNINFO);
221-
startpoint=walrcv->receivedUpto;
221+
startpoint=walrcv->receiveStart;
222222
SpinLockRelease(&walrcv->mutex);
223223

224224
/* Arrange to clean up at walreceiver exit */
@@ -558,8 +558,11 @@ XLogWalRcvFlush(bool dying)
558558

559559
/* Update shared-memory status */
560560
SpinLockAcquire(&walrcv->mutex);
561-
walrcv->latestChunkStart=walrcv->receivedUpto;
562-
walrcv->receivedUpto=LogstreamResult.Flush;
561+
if (XLByteLT(walrcv->receivedUpto,LogstreamResult.Flush))
562+
{
563+
walrcv->latestChunkStart=walrcv->receivedUpto;
564+
walrcv->receivedUpto=LogstreamResult.Flush;
565+
}
563566
SpinLockRelease(&walrcv->mutex);
564567

565568
/* Signal the startup process that new WAL has arrived */

‎src/backend/replication/walreceiverfuncs.c

Lines changed: 11 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -199,8 +199,17 @@ RequestXLogStreaming(XLogRecPtr recptr, const char *conninfo)
199199
walrcv->walRcvState=WALRCV_STARTING;
200200
walrcv->startTime=now;
201201

202-
walrcv->receivedUpto=recptr;
203-
walrcv->latestChunkStart=recptr;
202+
/*
203+
* If this is the first startup of walreceiver, we initialize
204+
* receivedUpto and latestChunkStart to receiveStart.
205+
*/
206+
if (walrcv->receiveStart.xlogid==0&&
207+
walrcv->receiveStart.xrecoff==0)
208+
{
209+
walrcv->receivedUpto=recptr;
210+
walrcv->latestChunkStart=recptr;
211+
}
212+
walrcv->receiveStart=recptr;
204213

205214
SpinLockRelease(&walrcv->mutex);
206215

‎src/include/replication/walreceiver.h

Lines changed: 10 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -51,12 +51,18 @@ typedef struct
5151
WalRcvStatewalRcvState;
5252
pg_time_tstartTime;
5353

54+
/*
55+
* receiveStart is the first byte position that will be received.
56+
* When startup process starts the walreceiver, it sets receiveStart
57+
* to the point where it wants the streaming to begin.
58+
*/
59+
XLogRecPtrreceiveStart;
60+
5461
/*
5562
* receivedUpto-1 is the last byte position that has already been
56-
* received. When startup process starts the walreceiver, it sets
57-
* receivedUpto to the point where it wants the streaming to begin. After
58-
* that, walreceiver updates this whenever it flushes the received WAL to
59-
* disk.
63+
* received. At the first startup of walreceiver, receivedUpto is
64+
* set to receiveStart. After that, walreceiver updates this whenever
65+
* it flushes the received WAL to disk.
6066
*/
6167
XLogRecPtrreceivedUpto;
6268

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