Avoid deadlock during orphan temp table removal.
If temp tables have dependencies (such as sequences) then it's
possible for autovacuum's cleanup of orphan temp tables to deadlock
against an incoming backend that's trying to clean out the temp
namespace for its own use. That can happen because RemoveTempRelations'
performDeletion call can visit objects within the namespace in
an order different from the order in which a per-table deletion
will visit them.
To fix, observe that performDeletion will begin by taking an exclusive
lock on the temp namespace (even though it won't actually delete it).
So, if we can get a shared lock on the namespace, we can be sure we're
not running concurrently with RemoveTempRelations, while also not
conflicting with ordinary use of the namespace. This requires
introducing a conditional version of LockDatabaseObject, but that's no
big deal. (It's surprising we've got along without that this long.)
Report and patch by Mikhail Zhilin. Back-patch to all supported
branches.
Discussion: https://postgr.es/m/c43ce028-2bc2-4865-9b89-3f706246eed5@postgrespro.ru
Branch
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REL_12_STABLE
Details
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https://git.postgresql.org/pg/commitdiff/f5d9212e53913d091e63f081e136f08b5c1595ff
Modified Files
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src/backend/postmaster/autovacuum.c | 21 +++++++++++++++++++-
src/backend/storage/lmgr/lmgr.c | 38 +++++++++++++++++++++++++++++++++++++
src/include/storage/lmgr.h | 2 ++
3 files changed, 60 insertions(+), 1 deletion(-)