Function IsIndexIsValidForQuery

pg_documentdb/src/index_am/rum.c:834–909

* Validates whether an index path descriptor * can be satisfied by the current index. */

 * can be satisfied by the current index.
 */
static bool
IsIndexIsValidForQuery(IndexPath *path)
{
	if (IsA(path, IndexOnlyScan))
	{
		/* We don't support index only scans in RUM */
		return false;
	}

	if (path->indexorderbys != NIL &&
		!ValidateMatchForOrderbyQuals(path))
	{
		/* Only return valid cost if the order by present
		 * matches the index fully
		 */
		return false;
	}

	if (list_length(path->indexclauses) >= 1)
	{
		/* if there's at least one other index clause,
		 * then this index is already valid
		 */
		return true;
	}

	if (path->indexinfo->indpred == NIL)
	{
		/*
		 * if the index is not a partial index, the useful_predicate
		 * clause does not apply. If there's no filter clauses, we
		 * can't really use this index (don't wanna do a full index scan)
		 */
		return false;
	}

	if (path->indexinfo->indpred != NIL)
	{
		ListCell *cell;
		foreach(cell, path->indexinfo->indpred)
		{
			Node *predQual = (Node *) lfirst(cell);

			/* walk the index predicates and check if they match the index */
			/* TODO: Do we need a query walk here */
			if (IsA(predQual, OpExpr))
			{
				OpExpr *expr = (OpExpr *) predQual;
				for (int32_t indexCol = 0; indexCol < path->indexinfo->nkeycolumns;
					 indexCol++)
				{
					if (MatchClauseWithIndexForFuncExpr(path, indexCol, expr->opfuncid,
														expr->args))
					{
						return true;
					}
				}
			}