Example #1
0
/* ----------------------------------------------------------------
 *		BitmapHeapNext
 *
 *		Retrieve next tuple from the BitmapHeapScan node's currentRelation
 * ----------------------------------------------------------------
 */
static TupleTableSlot *
BitmapHeapNext(BitmapHeapScanState *node)
{
	ExprContext *econtext;
	HeapScanDesc scan;
	TIDBitmap  *tbm;
	TBMIterator *tbmiterator;
	TBMIterateResult *tbmres;
	TBMIterator *prefetch_iterator;
	OffsetNumber targoffset;
	TupleTableSlot *slot;

	/*
	 * extract necessary information from index scan node
	 */
	econtext = node->ss.ps.ps_ExprContext;
	slot = node->ss.ss_ScanTupleSlot;
	scan = node->ss.ss_currentScanDesc;
	tbm = node->tbm;
	tbmiterator = node->tbmiterator;
	tbmres = node->tbmres;
	prefetch_iterator = node->prefetch_iterator;

	/*
	 * If we haven't yet performed the underlying index scan, do it, and begin
	 * the iteration over the bitmap.
	 *
	 * For prefetching, we use *two* iterators, one for the pages we are
	 * actually scanning and another that runs ahead of the first for
	 * prefetching.  node->prefetch_pages tracks exactly how many pages ahead
	 * the prefetch iterator is.  Also, node->prefetch_target tracks the
	 * desired prefetch distance, which starts small and increases up to the
	 * GUC-controlled maximum, target_prefetch_pages.  This is to avoid doing
	 * a lot of prefetching in a scan that stops after a few tuples because of
	 * a LIMIT.
	 */
	if (tbm == NULL)
	{
		tbm = (TIDBitmap *) MultiExecProcNode(outerPlanState(node));

		if (!tbm || !IsA(tbm, TIDBitmap))
			elog(ERROR, "unrecognized result from subplan");

		node->tbm = tbm;
		node->tbmiterator = tbmiterator = tbm_begin_iterate(tbm);
		node->tbmres = tbmres = NULL;

#ifdef USE_PREFETCH
		if (target_prefetch_pages > 0)
		{
			node->prefetch_iterator = prefetch_iterator = tbm_begin_iterate(tbm);
			node->prefetch_pages = 0;
			node->prefetch_target = -1;
		}
#endif   /* USE_PREFETCH */
	}

	for (;;)
	{
		Page		dp;
		ItemId		lp;

		/*
		 * Get next page of results if needed
		 */
		if (tbmres == NULL)
		{
			node->tbmres = tbmres = tbm_iterate(tbmiterator);
			if (tbmres == NULL)
			{
				/* no more entries in the bitmap */
				break;
			}

#ifdef USE_PREFETCH
			if (node->prefetch_pages > 0)
			{
				/* The main iterator has closed the distance by one page */
				node->prefetch_pages--;
			}
			else if (prefetch_iterator)
			{
				/* Do not let the prefetch iterator get behind the main one */
				TBMIterateResult *tbmpre = tbm_iterate(prefetch_iterator);

				if (tbmpre == NULL || tbmpre->blockno != tbmres->blockno)
					elog(ERROR, "prefetch and main iterators are out of sync");
			}
#endif   /* USE_PREFETCH */

			/*
			 * Ignore any claimed entries past what we think is the end of the
			 * relation.  (This is probably not necessary given that we got at
			 * least AccessShareLock on the table before performing any of the
			 * indexscans, but let's be safe.)
			 */
			if (tbmres->blockno >= scan->rs_nblocks)
			{
				node->tbmres = tbmres = NULL;
				continue;
			}

			/*
			 * Fetch the current heap page and identify candidate tuples.
			 */
			bitgetpage(scan, tbmres);

			/*
			 * Set rs_cindex to first slot to examine
			 */
			scan->rs_cindex = 0;

#ifdef USE_PREFETCH

			/*
			 * Increase prefetch target if it's not yet at the max.  Note that
			 * we will increase it to zero after fetching the very first
			 * page/tuple, then to one after the second tuple is fetched, then
			 * it doubles as later pages are fetched.
			 */
			if (node->prefetch_target >= target_prefetch_pages)
				 /* don't increase any further */ ;
			else if (node->prefetch_target >= target_prefetch_pages / 2)
				node->prefetch_target = target_prefetch_pages;
			else if (node->prefetch_target > 0)
				node->prefetch_target *= 2;
			else
				node->prefetch_target++;
#endif   /* USE_PREFETCH */
		}
		else
		{
			/*
			 * Continuing in previously obtained page; advance rs_cindex
			 */
			scan->rs_cindex++;

#ifdef USE_PREFETCH

			/*
			 * Try to prefetch at least a few pages even before we get to the
			 * second page if we don't stop reading after the first tuple.
			 */
			if (node->prefetch_target < target_prefetch_pages)
				node->prefetch_target++;
#endif   /* USE_PREFETCH */
		}

		/*
		 * Out of range?  If so, nothing more to look at on this page
		 */
		if (scan->rs_cindex < 0 || scan->rs_cindex >= scan->rs_ntuples)
		{
			node->tbmres = tbmres = NULL;
			continue;
		}

#ifdef USE_PREFETCH

		/*
		 * We issue prefetch requests *after* fetching the current page to try
		 * to avoid having prefetching interfere with the main I/O. Also, this
		 * should happen only when we have determined there is still something
		 * to do on the current page, else we may uselessly prefetch the same
		 * page we are just about to request for real.
		 */
		if (prefetch_iterator)
		{
			while (node->prefetch_pages < node->prefetch_target)
			{
				TBMIterateResult *tbmpre = tbm_iterate(prefetch_iterator);

				if (tbmpre == NULL)
				{
					/* No more pages to prefetch */
					tbm_end_iterate(prefetch_iterator);
					node->prefetch_iterator = prefetch_iterator = NULL;
					break;
				}
				node->prefetch_pages++;
				PrefetchBuffer(scan->rs_rd, MAIN_FORKNUM, tbmpre->blockno);
			}
		}
#endif   /* USE_PREFETCH */

		/*
		 * Okay to fetch the tuple
		 */
		targoffset = scan->rs_vistuples[scan->rs_cindex];
		dp = (Page) BufferGetPage(scan->rs_cbuf);
		lp = PageGetItemId(dp, targoffset);
		Assert(ItemIdIsNormal(lp));

		scan->rs_ctup.t_data = (HeapTupleHeader) PageGetItem((Page) dp, lp);
		scan->rs_ctup.t_len = ItemIdGetLength(lp);
		ItemPointerSet(&scan->rs_ctup.t_self, tbmres->blockno, targoffset);

		pgstat_count_heap_fetch(scan->rs_rd);

		/*
		 * Set up the result slot to point to this tuple. Note that the slot
		 * acquires a pin on the buffer.
		 */
		ExecStoreTuple(&scan->rs_ctup,
					   slot,
					   scan->rs_cbuf,
					   false);

		/*
		 * If we are using lossy info, we have to recheck the qual conditions
		 * at every tuple.
		 */
		if (tbmres->recheck)
		{
			econtext->ecxt_scantuple = slot;
			ResetExprContext(econtext);

			if (!ExecQual(node->bitmapqualorig, econtext, false))
			{
				/* Fails recheck, so drop it and loop back for another */
				ExecClearTuple(slot);
				continue;
			}
		}

		/* OK to return this tuple */
		return slot;
	}

	/*
	 * if we get here it means we are at the end of the scan..
	 */
	return ExecClearTuple(slot);
}
/*
 * BitmapPrefetch - Prefetch, if prefetch_pages are behind prefetch_target
 */
static inline void
BitmapPrefetch(BitmapHeapScanState *node, HeapScanDesc scan)
{
#ifdef USE_PREFETCH
	ParallelBitmapHeapState *pstate = node->pstate;

	if (pstate == NULL)
	{
		TBMIterator *prefetch_iterator = node->prefetch_iterator;

		if (prefetch_iterator)
		{
			while (node->prefetch_pages < node->prefetch_target)
			{
				TBMIterateResult *tbmpre = tbm_iterate(prefetch_iterator);

				if (tbmpre == NULL)
				{
					/* No more pages to prefetch */
					tbm_end_iterate(prefetch_iterator);
					node->prefetch_iterator = NULL;
					break;
				}
				node->prefetch_pages++;
				PrefetchBuffer(scan->rs_rd, MAIN_FORKNUM, tbmpre->blockno);
			}
		}

		return;
	}

	if (pstate->prefetch_pages < pstate->prefetch_target)
	{
		TBMSharedIterator *prefetch_iterator = node->shared_prefetch_iterator;

		if (prefetch_iterator)
		{
			while (1)
			{
				TBMIterateResult *tbmpre;
				bool		do_prefetch = false;

				/*
				 * Recheck under the mutex. If some other process has already
				 * done enough prefetching then we need not to do anything.
				 */
				SpinLockAcquire(&pstate->mutex);
				if (pstate->prefetch_pages < pstate->prefetch_target)
				{
					pstate->prefetch_pages++;
					do_prefetch = true;
				}
				SpinLockRelease(&pstate->mutex);

				if (!do_prefetch)
					return;

				tbmpre = tbm_shared_iterate(prefetch_iterator);
				if (tbmpre == NULL)
				{
					/* No more pages to prefetch */
					tbm_end_shared_iterate(prefetch_iterator);
					node->shared_prefetch_iterator = NULL;
					break;
				}

				PrefetchBuffer(scan->rs_rd, MAIN_FORKNUM, tbmpre->blockno);
			}
		}
	}
#endif							/* USE_PREFETCH */
}
Example #3
0
/*
 * pg_prewarm(regclass, mode text, fork text,
 *			  first_block int8, last_block int8)
 *
 * The first argument is the relation to be prewarmed; the second controls
 * how prewarming is done; legal options are 'prefetch', 'read', and 'buffer'.
 * The third is the name of the relation fork to be prewarmed.  The fourth
 * and fifth arguments specify the first and last block to be prewarmed.
 * If the fourth argument is NULL, it will be taken as 0; if the fifth argument
 * is NULL, it will be taken as the number of blocks in the relation.  The
 * return value is the number of blocks successfully prewarmed.
 */
Datum
pg_prewarm(PG_FUNCTION_ARGS)
{
	Oid			relOid;
	text	   *forkName;
	text	   *type;
	int64		first_block;
	int64		last_block;
	int64		nblocks;
	int64		blocks_done = 0;
	int64		block;
	Relation	rel;
	ForkNumber	forkNumber;
	char	   *forkString;
	char	   *ttype;
	PrewarmType ptype;
	AclResult	aclresult;

	/* Basic sanity checking. */
	if (PG_ARGISNULL(0))
		ereport(ERROR,
				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
				 errmsg("relation cannot be null")));
	relOid = PG_GETARG_OID(0);
	if (PG_ARGISNULL(1))
		ereport(ERROR,
				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
				 (errmsg("prewarm type cannot be null"))));
	type = PG_GETARG_TEXT_P(1);
	ttype = text_to_cstring(type);
	if (strcmp(ttype, "prefetch") == 0)
		ptype = PREWARM_PREFETCH;
	else if (strcmp(ttype, "read") == 0)
		ptype = PREWARM_READ;
	else if (strcmp(ttype, "buffer") == 0)
		ptype = PREWARM_BUFFER;
	else
	{
		ereport(ERROR,
				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
				 errmsg("invalid prewarm type"),
				 errhint("Valid prewarm types are \"prefetch\", \"read\", and \"buffer\".")));
		PG_RETURN_INT64(0);		/* Placate compiler. */
	}
	if (PG_ARGISNULL(2))
		ereport(ERROR,
				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
				 (errmsg("relation fork cannot be null"))));
	forkName = PG_GETARG_TEXT_P(2);
	forkString = text_to_cstring(forkName);
	forkNumber = forkname_to_number(forkString);

	/* Open relation and check privileges. */
	rel = relation_open(relOid, AccessShareLock);
	aclresult = pg_class_aclcheck(relOid, GetUserId(), ACL_SELECT);
	if (aclresult != ACLCHECK_OK)
		aclcheck_error(aclresult, ACL_KIND_CLASS, get_rel_name(relOid));

	/* Check that the fork exists. */
	RelationOpenSmgr(rel);
	if (!smgrexists(rel->rd_smgr, forkNumber))
		ereport(ERROR,
				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
				 errmsg("fork \"%s\" does not exist for this relation",
						forkString)));

	/* Validate block numbers, or handle nulls. */
	nblocks = RelationGetNumberOfBlocksInFork(rel, forkNumber);
	if (PG_ARGISNULL(3))
		first_block = 0;
	else
	{
		first_block = PG_GETARG_INT64(3);
		if (first_block < 0 || first_block >= nblocks)
			ereport(ERROR,
					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
					 errmsg("starting block number must be between 0 and " INT64_FORMAT,
							nblocks - 1)));
	}
	if (PG_ARGISNULL(4))
		last_block = nblocks - 1;
	else
	{
		last_block = PG_GETARG_INT64(4);
		if (last_block < 0 || last_block >= nblocks)
			ereport(ERROR,
					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
			errmsg("ending block number must be between 0 and " INT64_FORMAT,
				   nblocks - 1)));
	}

	/* Now we're ready to do the real work. */
	if (ptype == PREWARM_PREFETCH)
	{
#ifdef USE_PREFETCH

		/*
		 * In prefetch mode, we just hint the OS to read the blocks, but we
		 * don't know whether it really does it, and we don't wait for it to
		 * finish.
		 *
		 * It would probably be better to pass our prefetch requests in chunks
		 * of a megabyte or maybe even a whole segment at a time, but there's
		 * no practical way to do that at present without a gross modularity
		 * violation, so we just do this.
		 */
		for (block = first_block; block <= last_block; ++block)
		{
			CHECK_FOR_INTERRUPTS();
			PrefetchBuffer(rel, forkNumber, block);
			++blocks_done;
		}
#else
		ereport(ERROR,
				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
				 errmsg("prefetch is not supported by this build")));
#endif
	}
	else if (ptype == PREWARM_READ)
	{
		/*
		 * In read mode, we actually read the blocks, but not into shared
		 * buffers.  This is more portable than prefetch mode (it works
		 * everywhere) and is synchronous.
		 */
		for (block = first_block; block <= last_block; ++block)
		{
			CHECK_FOR_INTERRUPTS();
			smgrread(rel->rd_smgr, forkNumber, block, blockbuffer);
			++blocks_done;
		}
	}
	else if (ptype == PREWARM_BUFFER)
	{
		/*
		 * In buffer mode, we actually pull the data into shared_buffers.
		 */
		for (block = first_block; block <= last_block; ++block)
		{
			Buffer		buf;

			CHECK_FOR_INTERRUPTS();
			buf = ReadBufferExtended(rel, forkNumber, block, RBM_NORMAL, NULL);
			ReleaseBuffer(buf);
			++blocks_done;
		}
	}

	/* Close relation, release lock. */
	relation_close(rel, AccessShareLock);

	PG_RETURN_INT64(blocks_done);
}
Example #4
0
/*
 * BitmapPrefetch - Prefetch, if prefetch_pages are behind prefetch_target
 */
static inline void
BitmapPrefetch(BitmapHeapScanState *node, HeapScanDesc scan)
{
#ifdef USE_PREFETCH
	ParallelBitmapHeapState *pstate = node->pstate;

	if (pstate == NULL)
	{
		TBMIterator *prefetch_iterator = node->prefetch_iterator;

		if (prefetch_iterator)
		{
			while (node->prefetch_pages < node->prefetch_target)
			{
				TBMIterateResult *tbmpre = tbm_iterate(prefetch_iterator);
				bool		skip_fetch;

				if (tbmpre == NULL)
				{
					/* No more pages to prefetch */
					tbm_end_iterate(prefetch_iterator);
					node->prefetch_iterator = NULL;
					break;
				}
				node->prefetch_pages++;

				/*
				 * If we expect not to have to actually read this heap page,
				 * skip this prefetch call, but continue to run the prefetch
				 * logic normally.  (Would it be better not to increment
				 * prefetch_pages?)
				 *
				 * This depends on the assumption that the index AM will
				 * report the same recheck flag for this future heap page as
				 * it did for the current heap page; which is not a certainty
				 * but is true in many cases.
				 */
				skip_fetch = (node->can_skip_fetch &&
							  (node->tbmres ? !node->tbmres->recheck : false) &&
							  VM_ALL_VISIBLE(node->ss.ss_currentRelation,
											 tbmpre->blockno,
											 &node->pvmbuffer));

				if (!skip_fetch)
					PrefetchBuffer(scan->rs_rd, MAIN_FORKNUM, tbmpre->blockno);
			}
		}

		return;
	}

	if (pstate->prefetch_pages < pstate->prefetch_target)
	{
		TBMSharedIterator *prefetch_iterator = node->shared_prefetch_iterator;

		if (prefetch_iterator)
		{
			while (1)
			{
				TBMIterateResult *tbmpre;
				bool		do_prefetch = false;
				bool		skip_fetch;

				/*
				 * Recheck under the mutex. If some other process has already
				 * done enough prefetching then we need not to do anything.
				 */
				SpinLockAcquire(&pstate->mutex);
				if (pstate->prefetch_pages < pstate->prefetch_target)
				{
					pstate->prefetch_pages++;
					do_prefetch = true;
				}
				SpinLockRelease(&pstate->mutex);

				if (!do_prefetch)
					return;

				tbmpre = tbm_shared_iterate(prefetch_iterator);
				if (tbmpre == NULL)
				{
					/* No more pages to prefetch */
					tbm_end_shared_iterate(prefetch_iterator);
					node->shared_prefetch_iterator = NULL;
					break;
				}

				/* As above, skip prefetch if we expect not to need page */
				skip_fetch = (node->can_skip_fetch &&
							  (node->tbmres ? !node->tbmres->recheck : false) &&
							  VM_ALL_VISIBLE(node->ss.ss_currentRelation,
											 tbmpre->blockno,
											 &node->pvmbuffer));

				if (!skip_fetch)
					PrefetchBuffer(scan->rs_rd, MAIN_FORKNUM, tbmpre->blockno);
			}
		}
	}
#endif							/* USE_PREFETCH */
}