pgsql: Fix relcache reference leak when decoding TRUNCATE

Fix relcache reference leak when decoding TRUNCATE

ReorderBufferProcessTXN() opens every relation referenced by a
TRUNCATE change. When RelationIsLogicallyLogged() returns false,
it skips the relation without releasing the reference acquired
by RelationIdGetRelation().

Looking at the in-core code paths building XLOG_HEAP_TRUNCATE records,
no relation OIDs would be included if they do not satisfy
RelationIsLogicallyLogged(). One pattern that could go through is if a
table is switched to SET UNLOGGED, but that would not be reachable in
practice as the decoding happens after a historical snapshot is taken,
so the relation should still be valid.

This is a defense-in-depth measure in practice, and we tend to be
careful about how Relations are handled when sending changes to output
plugins, so backpatch all the way down.

Author: Chao Li <li(dot)evan(dot)chao(at)gmail(dot)com>
Reviewed-by: Xuneng Zhou <xunengzhou(at)gmail(dot)com>
Discussion: https://postgr.es/m/7DD65D03-3B5A-43B2-99AD-8E6AF5372BAB@gmail.com
Backpatch-through: 14

Branch
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REL_17_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/26a9d8ea643520856ca558b926970e70fcbbf6dc

Modified Files
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src/backend/replication/logical/reorderbuffer.c | 3 +++
1 file changed, 3 insertions(+)