Reset hot standby xmin after restart

Hot_standby_feedback could be reset by reload and worked correctly, but if
the server was restarted rather than reloaded the xmin was not reset.
Force reset always if hot_standby_feedback is enabled at startup.

Ants Aasma, Craig Ringer

Reported-by: Ants Aasma

diff --git a/src/backend/replication/walreceiver.c b/src/backend/replication/walreceiver.c
index 41e57f24397348c183d3a1eab77455042644375b..42f6c26f28b0d3aebc57dae654026614bf6ab578 100644 (file)
--- a/src/backend/replication/walreceiver.c
+++ b/src/backend/replication/walreceiver.c
@@ -1093,7 +1093,10 @@ XLogWalRcvSendReply(bool force, bool requestReply)
  * in case they don't have a watch.
  *
  * If the user disables feedback, send one final message to tell sender
- * to forget about the xmin on this standby.
+ * to forget about the xmin on this standby. We also send this message
+ * on first connect because a previous connection might have set xmin
+ * on a replication slot. (If we're not using a slot it's harmless to
+ * send a feedback message explicitly setting InvalidTransactionId).
  */
 static void
 XLogWalRcvSendHSFeedback(bool immed)
@@ -1103,7 +1106,8 @@ XLogWalRcvSendHSFeedback(bool immed)
        uint32          nextEpoch;
        TransactionId xmin;
        static TimestampTz sendTime = 0;
-       static bool master_has_standby_xmin = false;
+       /* initially true so we always send at least one feedback message */
+       static bool master_has_standby_xmin = true;
 
        /*
         * If the user doesn't want status to be reported to the master, be sure
@@ -1128,14 +1132,17 @@ XLogWalRcvSendHSFeedback(bool immed)
        }
 
        /*
-        * If Hot Standby is not yet active there is nothing to send. Check this
-        * after the interval has expired to reduce number of calls.
+        * If Hot Standby is not yet accepting connections there is nothing to
+        * send. Check this after the interval has expired to reduce number of
+        * calls.
+        *
+        * Bailing out here also ensures that we don't send feedback until we've
+        * read our own replication slot state, so we don't tell the master to
+        * discard needed xmin or catalog_xmin from any slots that may exist
+        * on this replica.
         */
        if (!HotStandbyActive())
-       {
-               Assert(!master_has_standby_xmin);
                return;
-       }
 
        /*
         * Make the expensive call to get the oldest xmin once we are certain