On Thu, 22 Nov 2018 at 22:33, Rushabh Lathia <rushabh.lathia@gmail.com> wrote: > CREATE TABLE foo (x int primary key); > INSERT INTO foo VALUES (1), (2), (3), (4), (5); > > CREATE OR REPLACE FUNCTION f1(a int) RETURNS int > AS $$ > BEGIN > DELETE FROM foo where x = a; > return 0; > END; > $$ LANGUAGE plpgsql; > > postgres@100858=#set plan_cache_mode = force_generic_plan; > SET > postgres@100858=#select f1(4); > f1 > ---- > 0 > (1 row) > > postgres@100858=#select f1(4); > server closed the connection unexpectedly
> Now, to fix this issue either we need to hold proper lock before reaching > to ExecInitIndexScan() or teach ExecInitIndexScan() to take AccessShareLock > on the scan coming from CMD_DELETE.
I'd say the following comment and code in nodeIndexscan.c is outdated:
/* * Open the index relation. * * If the parent table is one of the target relations of the query, then * InitPlan already opened and write-locked the index, so we can avoid * taking another lock here. Otherwise we need a normal reader's lock. */ relistarget = ExecRelationIsTargetRelation(estate, node->scan.scanrelid); indexstate->iss_RelationDesc = index_open(node->indexid, relistarget ? NoLock : AccessShareLock);
Despite what the above comment claims, these indexes have not been opened in InitPlan since 389af951552ff2. As you mentioned, they're opened in nodeModifyTable.c for non-delete statements.
+1.
I tried the same approach and with further testing I haven't found
any issues.
I think we either need to update the above code to align it to what's now in nodeModifyTable.c, or just obtain an AccessShareLock regardless. I kinda think we should just take the lock regardless as determining if the relation is a result relation may be much more expensive than just taking another lower-level lock on the index.
Anyway. I've attached a small patch to update the above fragment.
