Fix tuple routing to initialize batching only for inserts

A cross-partition update on a partitioned table is implemented as a
delete followed by an insert. With foreign partitions, this was however
causing issues, because the FDW and core may disagree on when to enable
batching.  postgres_fdw was only allowing batching for plain inserts
(CMD_INSERT) while core was trying to batch the insert component of the
cross-partition update.  Fix by restricting core to apply batching only
to plain CMD_INSERT queries.

It's possible to allow batching for cross-partition updates, but that
will require more extensive changes, so better to leave that for a
separate patch.

Author: Amit Langote
Reviewed-by: Tomas Vondra, Takayuki Tsunakawa
Discussion: https://postgr.es/m/20200628151002.7x5laxwpgvkyiu3q@development

1 files changed, 11 insertions, 2 deletions

diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index 368997d9d1f..35b48575c59 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -1934,17 +1934,26 @@ static int
 postgresGetForeignModifyBatchSize(ResultRelInfo *resultRelInfo)
 {
 	int	batch_size;
+	PgFdwModifyState *fmstate = resultRelInfo->ri_FdwState ?
+							(PgFdwModifyState *) resultRelInfo->ri_FdwState :
+							NULL;
 
 	/* should be called only once */
 	Assert(resultRelInfo->ri_BatchSize == 0);
 
 	/*
+	 * Should never get called when the insert is being performed as part of
+	 * a row movement operation.
+	 */
+	Assert(fmstate == NULL || fmstate->aux_fmstate == NULL);
+
+	/*
 	 * In EXPLAIN without ANALYZE, ri_fdwstate is NULL, so we have to lookup
 	 * the option directly in server/table options. Otherwise just use the
 	 * value we determined earlier.
 	 */
-	if (resultRelInfo->ri_FdwState)
-		batch_size = ((PgFdwModifyState *) resultRelInfo->ri_FdwState)->batch_size;
+	if (fmstate)
+		batch_size = fmstate->batch_size;
 	else
 		batch_size = get_batch_size_option(resultRelInfo->ri_RelationDesc);