pgsql: Fix memory leak in SnapBuildSerialize.

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: [hidden email]
Diagnosed-by: [hidden email]
Author: Amit Kapila
Backpatch-through: 9.5
Discussion: https://postgr.es/m/033ab54c-6393-42ee-8ec9-2b399b5d8cde.funnyxj.fxj@...

Branch
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REL_13_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/0685c5c1b9225352bbaf4fe81c550f09508379ce

Modified Files
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src/backend/replication/logical/snapbuild.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)