Function ExecFindInitialMatchingSubPlans

src/backend/executor/execPartition.c:2056–2214

* ExecFindInitialMatchingSubPlans * Identify the set of subplans that cannot be eliminated by initial * pruning, disregarding any pruning constraints involving PARAM_EXEC * Params. * * If additional pruning passes will be required (because of PARAM_EXEC * Params), we must also update the translation data that allows conversion * of partition indexes into subplan indexes to account for th

 * 'nsubplans' must be passed as the total number of unpruned subplans.
 */
Bitmapset *
ExecFindInitialMatchingSubPlans(PartitionPruneState *prunestate, int nsubplans)
{
	Bitmapset  *result = NULL;
	MemoryContext oldcontext;
	int			i;

	/* Caller error if we get here without do_initial_prune */
	Assert(prunestate->do_initial_prune);

	/*
	 * Switch to a temp context to avoid leaking memory in the executor's
	 * query-lifespan memory context.
	 */
	oldcontext = MemoryContextSwitchTo(prunestate->prune_context);

	/*
	 * For each hierarchy, do the pruning tests, and add nondeletable
	 * subplans' indexes to "result".
	 */
	for (i = 0; i < prunestate->num_partprunedata; i++)
	{
		PartitionPruningData *prunedata;
		PartitionedRelPruningData *pprune;

		prunedata = prunestate->partprunedata[i];
		pprune = &prunedata->partrelprunedata[0];

		/* Perform pruning without using PARAM_EXEC Params */
		find_matching_subplans_recurse(prunedata, pprune, true, &result);

		/* Expression eval may have used space in node's ps_ExprContext too */
		if (pprune->initial_pruning_steps)
			ResetExprContext(pprune->initial_context.planstate->ps_ExprContext);
	}

	/* Add in any subplans that partition pruning didn't account for */
	result = bms_add_members(result, prunestate->other_subplans);

	MemoryContextSwitchTo(oldcontext);

	/* Copy result out of the temp context before we reset it */
	result = bms_copy(result);

	MemoryContextReset(prunestate->prune_context);

	/*
	 * If exec-time pruning is required and we pruned subplans above, then we
	 * must re-sequence the subplan indexes so that ExecFindMatchingSubPlans
	 * properly returns the indexes from the subplans which will remain after
	 * execution of this function.
	 *
	 * We can safely skip this when !do_exec_prune, even though that leaves
	 * invalid data in prunestate, because that data won't be consulted again
	 * (cf initial Assert in ExecFindMatchingSubPlans).
	 */
	if (prunestate->do_exec_prune && bms_num_members(result) < nsubplans)
	{