Fix memory leak in SnapBuildSerialize.

The memory for the snapshot was leaked while serializing it to disk during
logical decoding. This memory will be freed only once walsender stops
streaming the changes. This can lead to a huge memory increase when master
logs Standby Snapshot too frequently say when the user is trying to create
many replication slots.

Reported-by: funnyxj.fxj@alibaba-inc.com
Diagnosed-by: funnyxj.fxj@alibaba-inc.com
Author: Amit Kapila
Backpatch-through: 9.5
Discussion: https://postgr.es/m/033ab54c-6393-42ee-8ec9-2b399b5d8cde.funnyxj.fxj@alibaba-inc.com

diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index 15b07a54c1172b9606d71e4cf669a30d06f9f77b..71d510e305e142b9e955cc2b5379be3680befed5 100644 (file)
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -1488,7 +1488,7 @@ static void
 SnapBuildSerialize(SnapBuild *builder, XLogRecPtr lsn)
 {
        Size            needed_length;
-       SnapBuildOnDisk *ondisk;
+       SnapBuildOnDisk *ondisk = NULL;
        char       *ondisk_c;
        int                     fd;
        char            tmppath[MAXPGPATH];
@@ -1687,6 +1687,9 @@ SnapBuildSerialize(SnapBuild *builder, XLogRecPtr lsn)
 out:
        ReorderBufferSetRestartPoint(builder->reorder,
                                                                 builder->last_serialized_snapshot);
+       /* be tidy */
+       if (ondisk)
+               pfree(ondisk);
 }
 
 /*