0001-Mark-snapshot-consistent-when-all-running-txes-have.patch

From 67e902eef33da9e241c079eaed9ab12a88616296 Mon Sep 17 00:00:00 2001
From: Petr Jelinek <pjmodos@pjmodos.net>
Date: Sat, 10 Dec 2016 21:56:44 +0100
Subject: [PATCH 1/2] Mark snapshot consistent when all running txes have
 finished.

---
 src/backend/replication/logical/snapbuild.c | 29 +++++++++++++++++++++--------
 1 file changed, 21 insertions(+), 8 deletions(-)

diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index 8b59fc5..5836d52 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -1213,9 +1213,11 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * Build catalog decoding snapshot incrementally using information about
 	 * the currently running transactions. There are several ways to do that:
 	 *
-	 * a) There were no running transactions when the xl_running_xacts record
-	 *	  was inserted, jump to CONSISTENT immediately. We might find such a
-	 *	  state we were waiting for b) and c).
+	 * a) Either there were no running transactions when the xl_running_xacts
+	 *    record was inserted (we might find this while waiting for b) or c))
+	 *    or the running transactions we've been tracking have all finished
+	 *    by the time the xl_running_xacts was inserted. We can jump to
+	 *    CONSISTENT immediately.
 	 *
 	 * b) Wait for all toplevel transactions that were running to end. We
 	 *	  simply track the number of in-progress toplevel transactions and
@@ -1251,13 +1253,18 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	}
 
 	/*
-	 * a) No transaction were running, we can jump to consistent.
+	 * a) Either no transaction were running or we've been tracking running
+	 *    transactions and the new snapshot has them all finished, we can
+	 *    jump to consistent.
 	 *
-	 * NB: We might have already started to incrementally assemble a snapshot,
-	 * so we need to be careful to deal with that.
+	 * NB: Since we might have already started to incrementally assemble a
+	 * snapshot, we need to be careful to deal with that.
 	 */
-	if (running->xcnt == 0)
+	if (running->xcnt == 0 ||
+		(builder->running.xcnt > 0 &&
+		 running->oldestRunningXid > builder->running.xmax))
 	{
+
 		if (builder->start_decoding_at == InvalidXLogRecPtr ||
 			builder->start_decoding_at <= lsn)
 			/* can decode everything after this */
@@ -1278,10 +1285,16 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 
 		builder->state = SNAPBUILD_CONSISTENT;
 
+		/*
+		 * Give different log detail based on actual state for easier
+		 * debugging.
+		 */
 		ereport(LOG,
 				(errmsg("logical decoding found consistent point at %X/%X",
 						(uint32) (lsn >> 32), (uint32) lsn),
-				 errdetail("There are no running transactions.")));
+				 errdetail(running->xcnt == 0 ?
+						   "There are no running transactions." :
+						   "All running transactions have finished.")));
 
 		return false;
 	}
-- 
2.7.4