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 3e9d4cd79f95622cc8e3eaedfba7fa37271edce4..4ec0003550e4f858b0a0430e794f0c65afc449f7 100644 (file)
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -1485,7 +1485,7 @@ static void
 SnapBuildSerialize(SnapBuild *builder, XLogRecPtr lsn)
 {
        Size            needed_length;
-       SnapBuildOnDisk *ondisk;
+       SnapBuildOnDisk *ondisk = NULL;
        char       *ondisk_c;
        int                     fd;
        char            tmppath[MAXPGPATH];
@@ -1684,6 +1684,9 @@ SnapBuildSerialize(SnapBuild *builder, XLogRecPtr lsn)
 out:
        ReorderBufferSetRestartPoint(builder->reorder,
                                                                 builder->last_serialized_snapshot);
+       /* be tidy */
+       if (ondisk)
+               pfree(ondisk);
 }
 
 /*