Function ExecHashIncreaseNumBatches

src/backend/executor/nodeHash.c:1132–1329

* ExecHashIncreaseNumBatches * increase the original number of batches in order to reduce * current memory consumption */

 *		current memory consumption
 */
static void
ExecHashIncreaseNumBatches(HashJoinTable hashtable)
{
	int			oldnbatch = hashtable->nbatch;
	int			curbatch = hashtable->curbatch;
	int			nbatch;
	MemoryContext oldcxt;
	long		ninmemory;
	long		nfreed;
	HashMemoryChunk oldchunks;
	Size		spaceUsedBefore = hashtable->spaceUsed;
	Size		spaceFreed = 0;
	HashJoinTableStats *stats = hashtable->stats;

	/* do nothing if we've decided to shut off growth */
	if (!hashtable->growEnabled)
		return;

	/* safety check to avoid overflow */
	if (oldnbatch > Min(INT_MAX / 2, MaxAllocSize / (sizeof(void *) * 2)))
		return;

	/* A reusable hash table can only respill during first pass */
	AssertImply(hashtable->hjstate->reuse_hashtable, hashtable->first_pass);

	nbatch = oldnbatch * 2;
	Assert(nbatch > 1);

#ifdef HJDEBUG
	printf("Hashjoin %p: increasing nbatch to %d because space = %zu\n",
		   hashtable, nbatch, hashtable->spaceUsed);
#endif

	oldcxt = MemoryContextSwitchTo(hashtable->hashCxt);

	if (hashtable->innerBatchFile == NULL)
	{
		/* we had no file arrays before */
		hashtable->innerBatchFile = (BufFile **)
			palloc0(nbatch * sizeof(BufFile *));
		hashtable->outerBatchFile = (BufFile **)
			palloc0(nbatch * sizeof(BufFile *));
		/* time to establish the temp tablespaces, too */
		PrepareTempTablespaces();
	}
	else
	{
		/* enlarge arrays and zero out added entries */
		hashtable->innerBatchFile = (BufFile **)
			repalloc(hashtable->innerBatchFile, nbatch * sizeof(BufFile *));
		hashtable->outerBatchFile = (BufFile **)
			repalloc(hashtable->outerBatchFile, nbatch * sizeof(BufFile *));
		MemSet(hashtable->innerBatchFile + oldnbatch, 0,
			   (nbatch - oldnbatch) * sizeof(BufFile *));
		MemSet(hashtable->outerBatchFile + oldnbatch, 0,
			   (nbatch - oldnbatch) * sizeof(BufFile *));
	}