Function evalHashKey

src/backend/executor/nodeMotion.c:1087–1139

* Experimental code that will be replaced later with new hashing mechanism */

 * Experimental code that will be replaced later with new hashing mechanism
 */
uint32
evalHashKey(ExprContext *econtext, List *hashkeys, CdbHash * h)
{
	ListCell   *hk;
	MemoryContext oldContext;
	unsigned int target_seg;

	ResetExprContext(econtext);

	oldContext = MemoryContextSwitchTo(econtext->ecxt_per_tuple_memory);

	/*
	 * If we have 1 or more distribution keys for this relation, hash them.
	 * However, If this happens to be a relation with an empty policy
	 * (partitioning policy with a NULL distribution key list) then we have no
	 * hash key value to feed in, so use cdbhashrandomseg() to pick a segment
	 * at random.
	 */
	if (list_length(hashkeys) > 0)
	{
		int			i;

		cdbhashinit(h);

		i = 0;
		foreach(hk, hashkeys)
		{
			ExprState  *keyexpr = (ExprState *) lfirst(hk);
			Datum		keyval;
			bool		isNull;

			/*
			 * Get the attribute value of the tuple
			 */
			keyval = ExecEvalExpr(keyexpr, econtext, &isNull);

			/*
			 * Compute the hash function
			 */
			cdbhash(h, i + 1, keyval, isNull);
			i++;
		}
		target_seg = cdbhashreduce(h);
	}
	else
	{
		target_seg = cdbhashrandomseg(h->numsegs);
	}

	MemoryContextSwitchTo(oldContext);

	return target_seg;
}


void