f63a5ead9d
In what seems like a fit of misplaced optimization, ExtractReplicaIdentity() accessed the relation's replica-identity index without taking any lock on it. Usually, the surrounding query already holds some lock so this is safe enough ... but in the case of a previously-planned delete, there might be no existing lock. Given a suitable test case, this is exposed in v12 and HEAD by an assertion added by commit b04aeb0a0. The whole thing's rather poorly thought out anyway; rather than looking directly at the index, we should use the index-attributes bitmap that's held by the parent table's relcache entry, as the caller functions do. This is more consistent and likely a bit faster, since it avoids a cache lookup. Hence, change to doing it that way. While at it, rather than blithely assuming that the identity columns are non-null (with catastrophic results if that's wrong), add assertion checks that they aren't null. Possibly those should be actual test-and-elog, but I'll leave it like this for now. In principle, this is a bug that's been there since this code was introduced (in 9.4). In practice, the risk seems quite low, since we do have a lock on the index's parent table, so concurrent changes to the index's catalog entries seem unlikely. Given the precedent that commit 9c703c169 wasn't back-patched, I won't risk back-patching this further than v12. Per report from Hadi Moshayedi. Discussion: https://postgr.es/m/CAK=1=Wrek44Ese1V7LjKiQS-Nd-5LgLi_5_CskGbpggKEf3tKQ@mail.gmail.com
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