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commit    bee4a4d361c054c531c3a27024f9ff3efef3635b
Author:   Fujii Masao <fujii@postgresql.org>
Date:     Tue Jun 25 17:19:26 2013 +0000
First released in: 9.4.0, 9.1.10, 9.2.5, 9.3.0

    Support clean switchover.
    
    In replication, when we shutdown the master, walsender tries to send
    all the outstanding WAL records to the standby, and then to exit. This
    basically means that all the WAL records are fully synced between
    two servers after the clean shutdown of the master. So, after
    promoting the standby to new master, we can restart the stopped
    master as new standby without the need for a fresh backup from
    new master.
    
    But there was one problem so far: though walsender tries to send all
    the outstanding WAL records, it doesn't wait for them to be replicated
    to the standby. Then, before receiving all the WAL records,
    walreceiver can detect the closure of connection and exit. We cannot
    guarantee that there is no missing WAL in the standby after clean
    shutdown of the master. In this case, backup from new master is
    required when restarting the stopped master as new standby.
    
    This patch fixes this problem. It just changes walsender so that it
    waits for all the outstanding WAL records to be replicated to the
    standby before closing the replication connection.
    
    Per discussion, this is a fix that needs to get backpatched rather than
    new feature. So, back-patch to 9.1 where enough infrastructure for
    this exists.
    
    Patch by me, reviewed by Andres Freund.


 src/backend/replication/walsender.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 5c9314695fe..bd64c2873f7 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -22,7 +22,8 @@
  * If the server is shut down, postmaster sends us SIGUSR2 after all
  * regular backends have exited and the shutdown checkpoint has been written.
  * This instruct walsender to send any outstanding WAL, including the
- * shutdown checkpoint record, and then exit.
+ * shutdown checkpoint record, wait for it to be replicated to the standby,
+ * and then exit.
  *
  *
  * Portions Copyright (c) 2010-2012, PostgreSQL Global Development Group
@@ -800,7 +801,8 @@ WalSndLoop(void)
 
 			/*
 			 * When SIGUSR2 arrives, we send any outstanding logs up to the
-			 * shutdown checkpoint record (i.e., the latest record) and exit.
+			 * shutdown checkpoint record (i.e., the latest record), wait
+			 * for them to be replicated to the standby, and exit.
 			 * This may be a normal termination at shutdown, or a promotion,
 			 * the walsender is not sure which.
 			 */
@@ -808,7 +810,8 @@ WalSndLoop(void)
 			{
 				/* ... let's just be real sure we're caught up ... */
 				XLogSend(output_message, &caughtup);
-				if (caughtup && !pq_is_send_pending())
+				if (caughtup && XLByteEQ(sentPtr, MyWalSnd->flush) &&
+					!pq_is_send_pending())
 				{
 					walsender_shutdown_requested = true;
 					continue;	/* don't want to wait more */


[parent: 99ee15b315c1]