Function ExecHashTableCreate

src/backend/executor/nodeHash.c:538–782

---------------------------------------------------------------- * ExecHashTableCreate * * create an empty hashtable data structure for hashjoin. * ---------------------------------------------------------------- */

 * ----------------------------------------------------------------
 */
HashJoinTable
ExecHashTableCreate(HashState *state, HashJoinState *hjstate,
					List *hashOperators, List *hashCollations,
					bool keepNulls, uint64 operatorMemKB)
{
	Hash	   *node;
	HashJoinTable hashtable;
	Plan	   *outerNode;
	size_t		space_allowed;
	int			nbuckets;
	int			nbatch;
	double		rows;
	int			num_skew_mcvs;
	int			log2_nbuckets;
	int			nkeys;
	int			i;
	ListCell   *ho;
	ListCell   *hc;
	MemoryContext oldcxt;

	/*
	 * Get information about the size of the relation to be hashed (it's the
	 * "outer" subtree of this node, but the inner relation of the hashjoin).
	 * Compute the appropriate size of the hash table.
	 */
	node = (Hash *) state->ps.plan;
	outerNode = outerPlan(node);

	/*
	 * If this is shared hash table with a partial plan, then we can't use
	 * outerNode->plan_rows to estimate its size.  We need an estimate of the
	 * total number of rows across all copies of the partial plan.
	 */
	rows = node->plan.parallel_aware ? node->rows_total : outerNode->plan_rows;

	ExecChooseHashTableSize(rows, outerNode->plan_width,
							OidIsValid(node->skewTable),
							operatorMemKB,
							state->parallel_state != NULL,
							state->parallel_state != NULL ?
							state->parallel_state->nparticipants - 1 : 0,
							&space_allowed,
							&nbuckets, &nbatch, &num_skew_mcvs);

	/* nbuckets must be a power of 2 */
	log2_nbuckets = my_log2(nbuckets);
	Assert(nbuckets == (1 << log2_nbuckets));

	/*
	 * Initialize the hash table control block.
	 *
	 * The hashtable control block is just palloc'd from the executor's
	 * per-query memory context.  Everything else should be kept inside the
	 * subsidiary hashCxt or batchCxt.
	 */
	hashtable = (HashJoinTable) palloc0(sizeof(HashJoinTableData));
	hashtable->nbuckets = nbuckets;
	hashtable->nbuckets_original = nbuckets;