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 9b81874ce19be43e6e7e870c4a3096911448496e..521e5d238f1b5263a0367ed73a6ce42a33ae7fa4 100644 (file)
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -1486,7 +1486,7 @@ static void
 SnapBuildSerialize(SnapBuild *builder, XLogRecPtr lsn)
 {
        Size            needed_length;
-       SnapBuildOnDisk *ondisk;
+       SnapBuildOnDisk *ondisk = NULL;
        char       *ondisk_c;
        int                     fd;
        char            tmppath[MAXPGPATH];
@@ -1681,6 +1681,9 @@ SnapBuildSerialize(SnapBuild *builder, XLogRecPtr lsn)
 out:
        ReorderBufferSetRestartPoint(builder->reorder,
                                                                 builder->last_serialized_snapshot);
+       /* be tidy */
+       if (ondisk)
+               pfree(ondisk);
 }
 
 /*