We are using the foreign data wrapper API to integrate YugaByte DB (
https://github.com/yugabyte/yugabyte-db) with PostgreSQL, so scanning tables stored in YugaByte DB is being done through Foreign Scan callbacks. These callbacks in turn read data from the underlying YugaByte DB cluster and maintain reference counts on RPC-related resources needed for that. Currently we are using PostgreSQL 10.4 codebase for this integration. I am trying to figure out what is the right way for foreign data wrappers to ensure resources used in a query are freed in all cases. It looks like the EndForeignScan callback is not being called in case an error happens during expression evaluation, such as during this query from int2.sql:
SELECT '' AS five, i.f1, i.f1 * int2 '2' AS x FROM INT2_TBL i;
ERROR: smallint out of range
ExecEndForeignScan (postgres/src/backend/executor/nodeForeignscan.c:293)
ExecEndNode (postgres/src/backend/executor/execProcnode.c:649)
ExecEndPlan (postgres/src/backend/executor/execMain.c:1607)
standard_ExecutorEnd (postgres/src/backend/executor/execMain.c:495)
ExecutorEnd (postgres/src/backend/executor/execMain.c:466)
PortalCleanup (postgres/src/backend/commands/portalcmds.c:302)
PortalDrop (postgres/src/backend/utils/mmgr/portalmem.c:489)
exec_simple_query (postgres/src/backend/tcop/postgres.c:1118)
PostgresMain (postgres/src/backend/tcop/postgres.c:4126)
BackendRun (postgres/src/backend/postmaster/postmaster.c:4411)
BackendStartup (postgres/src/backend/postmaster/postmaster.c:4083)
ServerLoop (postgres/src/backend/postmaster/postmaster.c:1758)
PostmasterMain (postgres/src/backend/postmaster/postmaster.c:1366)
PostgresServerProcessMain (postgres/src/backend/main/main.c:228)
However, I see that ExecutorEnd is not being executed at all in PortalCleanup in portalcmds.c in case portal->status is PORTAL_FAILED. If this is by design, what would be the right callback mechanism for foreign data wrappers to ensure resources are freed?Would RegisterResourceReleaseCallback from resowner.h be more appropriate for this use case? I only see that being used for OpenSSL-related resources at the moment.
