+ nbytes = offsetof(ParallelIndexScanDescData, ps_snapshot_data);
+ nbytes = add_size(nbytes, EstimateSnapshotSpace(snapshot));
+ nbytes = MAXALIGN(nbytes);
+
+ /*
+ * If amestimateparallelscan is not provided, assume there is no
+ * AM-specific data needed. (It's hard to believe that could work, but
+ * it's easy enough to cater to it here.)
+ */
+ if (indexRelation->rd_amroutine->amestimateparallelscan != NULL)
+ nbytes = add_size(nbytes,
+ indexRelation->rd_amroutine->amestimateparallelscan());
+
+ return nbytes;
+}
+
+/*
+ * index_parallelscan_initialize - initialize parallel scan
+ *
+ * We initialize both the ParallelIndexScanDesc proper and the AM-specific
+ * information which follows it.
+ *
+ * This function calls access method specific initialization routine to
+ * initialize am specific information. Call this just once in the leader
+ * process; then, individual workers attach via index_beginscan_parallel.
+ */
+void
+index_parallelscan_initialize(Relation heapRelation, Relation indexRelation,
+ Snapshot snapshot, ParallelIndexScanDesc target)
+{
+ Size offset;
+
+ RELATION_CHECKS;
+
+ offset = add_size(offsetof(ParallelIndexScanDescData, ps_snapshot_data),
+ EstimateSnapshotSpace(snapshot));
+ offset = MAXALIGN(offset);
+
+ target->ps_relid = RelationGetRelid(heapRelation);
+ target->ps_indexid = RelationGetRelid(indexRelation);
+ target->ps_offset = offset;
+ SerializeSnapshot(snapshot, target->ps_snapshot_data);
+
+ /* aminitparallelscan is optional; assume no-op if not provided by AM */
+ if (indexRelation->rd_amroutine->aminitparallelscan != NULL)