Remove unnecessary failure cases in RemoveRoleFromObjectPolicy().

Enterprise / PostgreSQL - Tom Lane [sss.pgh.pa.us] - 25 June 2021 17:59 UTC

It's not really necessary for this function to open or lock the relation associated with the pg_policy entry it's modifying. The error checks it's making on the rel are if anything counterproductive (e.g., if we don't want to allow installation of policies on system catalogs, here is not the place to prevent that). In particular, it seems just wrong to insist on an ownership check. That has the net effect of forcing people to use superuser for DROP OWNED BY, which surely is not an effect we want. Also there is no point in rebuilding the dependencies of the policy expressions, which aren't being changed. Lastly, locking the table also seems counterproductive; it's not helping to prevent race conditions, since we failed to re-read the pg_policy row after acquiring the lock. That means that concurrent DDL would likely result in "tuple concurrently updated/deleted" errors; which is the same behavior this code will produce, with less overhead.

Per discussion of bug #17062. Back-patch to all supported versions, as the failure cases this eliminates seem just as undesirable in 9.6 as in HEAD.

Discussion: https://postgr.es/m/1573181.1624220108@sss.pgh.pa.us

5a0f1c8c01 Remove unnecessary failure cases in RemoveRoleFromObjectPolicy().
src/backend/commands/policy.c | 195 ++++++++++--------------------------------
1 file changed, 47 insertions(+), 148 deletions(-)

Upstream: git.postgresql.org


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