Exemplo n.º 1
0
/*
 * RegisterSnapshotOnOwner
 *		As above, but use the specified resource owner
 */
Snapshot
RegisterSnapshotOnOwner(Snapshot snapshot, ResourceOwner owner)
{
	Snapshot	snap;

	if (snapshot == InvalidSnapshot)
		return InvalidSnapshot;

	/* Static snapshot?  Create a persistent copy */
	snap = snapshot->copied ? snapshot : CopySnapshot(snapshot);

	/* and tell resowner.c about it */
	ResourceOwnerEnlargeSnapshots(owner);
	snap->regd_count++;
	ResourceOwnerRememberSnapshot(owner, snap);

	if (snap->regd_count == 1)
		pairingheap_add(&RegisteredSnapshots, &snap->ph_node);

	return snap;
}
Exemplo n.º 2
0
/*
 * Scan all items on the GiST index page identified by *pageItem, and insert
 * them into the queue (or directly to output areas)
 *
 * scan: index scan we are executing
 * pageItem: search queue item identifying an index page to scan
 * myDistances: distances array associated with pageItem, or NULL at the root
 * tbm: if not NULL, gistgetbitmap's output bitmap
 * ntids: if not NULL, gistgetbitmap's output tuple counter
 *
 * If tbm/ntids aren't NULL, we are doing an amgetbitmap scan, and heap
 * tuples should be reported directly into the bitmap.  If they are NULL,
 * we're doing a plain or ordered indexscan.  For a plain indexscan, heap
 * tuple TIDs are returned into so->pageData[].  For an ordered indexscan,
 * heap tuple TIDs are pushed into individual search queue items.  In an
 * index-only scan, reconstructed index tuples are returned along with the
 * TIDs.
 *
 * If we detect that the index page has split since we saw its downlink
 * in the parent, we push its new right sibling onto the queue so the
 * sibling will be processed next.
 */
static void
gistScanPage(IndexScanDesc scan, GISTSearchItem *pageItem, double *myDistances,
			 TIDBitmap *tbm, int64 *ntids)
{
	GISTScanOpaque so = (GISTScanOpaque) scan->opaque;
	GISTSTATE  *giststate = so->giststate;
	Relation	r = scan->indexRelation;
	Buffer		buffer;
	Page		page;
	GISTPageOpaque opaque;
	OffsetNumber maxoff;
	OffsetNumber i;
	MemoryContext oldcxt;

	Assert(!GISTSearchItemIsHeap(*pageItem));

	buffer = ReadBuffer(scan->indexRelation, pageItem->blkno);
	LockBuffer(buffer, GIST_SHARE);
	PredicateLockPage(r, BufferGetBlockNumber(buffer), scan->xs_snapshot);
	gistcheckpage(scan->indexRelation, buffer);
	page = BufferGetPage(buffer);
	TestForOldSnapshot(scan->xs_snapshot, r, page);
	opaque = GistPageGetOpaque(page);

	/*
	 * Check if we need to follow the rightlink. We need to follow it if the
	 * page was concurrently split since we visited the parent (in which case
	 * parentlsn < nsn), or if the system crashed after a page split but
	 * before the downlink was inserted into the parent.
	 */
	if (!XLogRecPtrIsInvalid(pageItem->data.parentlsn) &&
		(GistFollowRight(page) ||
		 pageItem->data.parentlsn < GistPageGetNSN(page)) &&
		opaque->rightlink != InvalidBlockNumber /* sanity check */ )
	{
		/* There was a page split, follow right link to add pages */
		GISTSearchItem *item;

		/* This can't happen when starting at the root */
		Assert(myDistances != NULL);

		oldcxt = MemoryContextSwitchTo(so->queueCxt);

		/* Create new GISTSearchItem for the right sibling index page */
		item = palloc(SizeOfGISTSearchItem(scan->numberOfOrderBys));
		item->blkno = opaque->rightlink;
		item->data.parentlsn = pageItem->data.parentlsn;

		/* Insert it into the queue using same distances as for this page */
		memcpy(item->distances, myDistances,
			   sizeof(double) * scan->numberOfOrderBys);

		pairingheap_add(so->queue, &item->phNode);

		MemoryContextSwitchTo(oldcxt);
	}

	so->nPageData = so->curPageData = 0;
	scan->xs_hitup = NULL;		/* might point into pageDataCxt */
	if (so->pageDataCxt)
		MemoryContextReset(so->pageDataCxt);

	/*
	 * We save the LSN of the page as we read it, so that we know whether it
	 * safe to apply LP_DEAD hints to the page later. This allows us to drop
	 * the pin for MVCC scans, which allows vacuum to avoid blocking.
	 */
	so->curPageLSN = BufferGetLSNAtomic(buffer);

	/*
	 * check all tuples on page
	 */
	maxoff = PageGetMaxOffsetNumber(page);
	for (i = FirstOffsetNumber; i <= maxoff; i = OffsetNumberNext(i))
	{
		ItemId		iid = PageGetItemId(page, i);
		IndexTuple	it;
		bool		match;
		bool		recheck;
		bool		recheck_distances;

		/*
		 * If the scan specifies not to return killed tuples, then we treat a
		 * killed tuple as not passing the qual.
		 */
		if (scan->ignore_killed_tuples && ItemIdIsDead(iid))
			continue;

		it = (IndexTuple) PageGetItem(page, iid);

		/*
		 * Must call gistindex_keytest in tempCxt, and clean up any leftover
		 * junk afterward.
		 */
		oldcxt = MemoryContextSwitchTo(so->giststate->tempCxt);

		match = gistindex_keytest(scan, it, page, i,
								  &recheck, &recheck_distances);

		MemoryContextSwitchTo(oldcxt);
		MemoryContextReset(so->giststate->tempCxt);

		/* Ignore tuple if it doesn't match */
		if (!match)
			continue;

		if (tbm && GistPageIsLeaf(page))
		{
			/*
			 * getbitmap scan, so just push heap tuple TIDs into the bitmap
			 * without worrying about ordering
			 */
			tbm_add_tuples(tbm, &it->t_tid, 1, recheck);
			(*ntids)++;
		}
		else if (scan->numberOfOrderBys == 0 && GistPageIsLeaf(page))
		{
			/*
			 * Non-ordered scan, so report tuples in so->pageData[]
			 */
			so->pageData[so->nPageData].heapPtr = it->t_tid;
			so->pageData[so->nPageData].recheck = recheck;
			so->pageData[so->nPageData].offnum = i;

			/*
			 * In an index-only scan, also fetch the data from the tuple.  The
			 * reconstructed tuples are stored in pageDataCxt.
			 */
			if (scan->xs_want_itup)
			{
				oldcxt = MemoryContextSwitchTo(so->pageDataCxt);
				so->pageData[so->nPageData].recontup =
					gistFetchTuple(giststate, r, it);
				MemoryContextSwitchTo(oldcxt);
			}
			so->nPageData++;
		}
		else
		{
			/*
			 * Must push item into search queue.  We get here for any lower
			 * index page, and also for heap tuples if doing an ordered
			 * search.
			 */
			GISTSearchItem *item;

			oldcxt = MemoryContextSwitchTo(so->queueCxt);

			/* Create new GISTSearchItem for this item */
			item = palloc(SizeOfGISTSearchItem(scan->numberOfOrderBys));

			if (GistPageIsLeaf(page))
			{
				/* Creating heap-tuple GISTSearchItem */
				item->blkno = InvalidBlockNumber;
				item->data.heap.heapPtr = it->t_tid;
				item->data.heap.recheck = recheck;
				item->data.heap.recheckDistances = recheck_distances;

				/*
				 * In an index-only scan, also fetch the data from the tuple.
				 */
				if (scan->xs_want_itup)
					item->data.heap.recontup = gistFetchTuple(giststate, r, it);
			}
			else
			{
				/* Creating index-page GISTSearchItem */
				item->blkno = ItemPointerGetBlockNumber(&it->t_tid);

				/*
				 * LSN of current page is lsn of parent page for child. We
				 * only have a shared lock, so we need to get the LSN
				 * atomically.
				 */
				item->data.parentlsn = BufferGetLSNAtomic(buffer);
			}

			/* Insert it into the queue using new distance data */
			memcpy(item->distances, so->distances,
				   sizeof(double) * scan->numberOfOrderBys);

			pairingheap_add(so->queue, &item->phNode);

			MemoryContextSwitchTo(oldcxt);
		}
	}

	UnlockReleaseBuffer(buffer);
}
Exemplo n.º 3
0
/*
 * SetTransactionSnapshot
 *		Set the transaction's snapshot from an imported MVCC snapshot.
 *
 * Note that this is very closely tied to GetTransactionSnapshot --- it
 * must take care of all the same considerations as the first-snapshot case
 * in GetTransactionSnapshot.
 */
static void
SetTransactionSnapshot(Snapshot sourcesnap, TransactionId sourcexid,
					   PGPROC *sourceproc)
{
	/* Caller should have checked this already */
	Assert(!FirstSnapshotSet);

	Assert(pairingheap_is_empty(&RegisteredSnapshots));
	Assert(FirstXactSnapshot == NULL);
	Assert(!HistoricSnapshotActive());

	/*
	 * Even though we are not going to use the snapshot it computes, we must
	 * call GetSnapshotData, for two reasons: (1) to be sure that
	 * CurrentSnapshotData's XID arrays have been allocated, and (2) to update
	 * RecentXmin and RecentGlobalXmin.  (We could alternatively include those
	 * two variables in exported snapshot files, but it seems better to have
	 * snapshot importers compute reasonably up-to-date values for them.)
	 */
	CurrentSnapshot = GetSnapshotData(&CurrentSnapshotData);

	/*
	 * Now copy appropriate fields from the source snapshot.
	 */
	CurrentSnapshot->xmin = sourcesnap->xmin;
	CurrentSnapshot->xmax = sourcesnap->xmax;
	CurrentSnapshot->xcnt = sourcesnap->xcnt;
	Assert(sourcesnap->xcnt <= GetMaxSnapshotXidCount());
	memcpy(CurrentSnapshot->xip, sourcesnap->xip,
		   sourcesnap->xcnt * sizeof(TransactionId));
	CurrentSnapshot->subxcnt = sourcesnap->subxcnt;
	Assert(sourcesnap->subxcnt <= GetMaxSnapshotSubxidCount());
	memcpy(CurrentSnapshot->subxip, sourcesnap->subxip,
		   sourcesnap->subxcnt * sizeof(TransactionId));
	CurrentSnapshot->suboverflowed = sourcesnap->suboverflowed;
	CurrentSnapshot->takenDuringRecovery = sourcesnap->takenDuringRecovery;
	/* NB: curcid should NOT be copied, it's a local matter */

	/*
	 * Now we have to fix what GetSnapshotData did with MyPgXact->xmin and
	 * TransactionXmin.  There is a race condition: to make sure we are not
	 * causing the global xmin to go backwards, we have to test that the
	 * source transaction is still running, and that has to be done
	 * atomically. So let procarray.c do it.
	 *
	 * Note: in serializable mode, predicate.c will do this a second time. It
	 * doesn't seem worth contorting the logic here to avoid two calls,
	 * especially since it's not clear that predicate.c *must* do this.
	 */
	if (sourceproc != NULL)
	{
		if (!ProcArrayInstallRestoredXmin(CurrentSnapshot->xmin, sourceproc))
			ereport(ERROR,
					(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
					 errmsg("could not import the requested snapshot"),
			   errdetail("The source transaction is not running anymore.")));
	}
	else if (!ProcArrayInstallImportedXmin(CurrentSnapshot->xmin, sourcexid))
		ereport(ERROR,
				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
				 errmsg("could not import the requested snapshot"),
			   errdetail("The source transaction %u is not running anymore.",
						 sourcexid)));

	/*
	 * In transaction-snapshot mode, the first snapshot must live until end of
	 * xact, so we must make a copy of it.  Furthermore, if we're running in
	 * serializable mode, predicate.c needs to do its own processing.
	 */
	if (IsolationUsesXactSnapshot())
	{
		if (IsolationIsSerializable())
			SetSerializableTransactionSnapshot(CurrentSnapshot, sourcexid);
		/* Make a saved copy */
		CurrentSnapshot = CopySnapshot(CurrentSnapshot);
		FirstXactSnapshot = CurrentSnapshot;
		/* Mark it as "registered" in FirstXactSnapshot */
		FirstXactSnapshot->regd_count++;
		pairingheap_add(&RegisteredSnapshots, &FirstXactSnapshot->ph_node);
	}

	FirstSnapshotSet = true;
}
Exemplo n.º 4
0
/*
 * GetTransactionSnapshot
 *		Get the appropriate snapshot for a new query in a transaction.
 *
 * Note that the return value may point at static storage that will be modified
 * by future calls and by CommandCounterIncrement().  Callers should call
 * RegisterSnapshot or PushActiveSnapshot on the returned snap if it is to be
 * used very long.
 */
Snapshot
GetTransactionSnapshot(void)
{
	/*
	 * Return historic snapshot if doing logical decoding. We'll never need a
	 * non-historic transaction snapshot in this (sub-)transaction, so there's
	 * no need to be careful to set one up for later calls to
	 * GetTransactionSnapshot().
	 */
	if (HistoricSnapshotActive())
	{
		Assert(!FirstSnapshotSet);
		return HistoricSnapshot;
	}

	/* First call in transaction? */
	if (!FirstSnapshotSet)
	{
		Assert(pairingheap_is_empty(&RegisteredSnapshots));
		Assert(FirstXactSnapshot == NULL);

		if (IsInParallelMode())
			elog(ERROR,
				 "cannot take query snapshot during a parallel operation");

		/*
		 * In transaction-snapshot mode, the first snapshot must live until
		 * end of xact regardless of what the caller does with it, so we must
		 * make a copy of it rather than returning CurrentSnapshotData
		 * directly.  Furthermore, if we're running in serializable mode,
		 * predicate.c needs to wrap the snapshot fetch in its own processing.
		 */
		if (IsolationUsesXactSnapshot())
		{
			/* First, create the snapshot in CurrentSnapshotData */
			if (IsolationIsSerializable())
				CurrentSnapshot = GetSerializableTransactionSnapshot(&CurrentSnapshotData);
			else
				CurrentSnapshot = GetSnapshotData(&CurrentSnapshotData);
			/* Make a saved copy */
			CurrentSnapshot = CopySnapshot(CurrentSnapshot);
			FirstXactSnapshot = CurrentSnapshot;
			/* Mark it as "registered" in FirstXactSnapshot */
			FirstXactSnapshot->regd_count++;
			pairingheap_add(&RegisteredSnapshots, &FirstXactSnapshot->ph_node);
		}
		else
			CurrentSnapshot = GetSnapshotData(&CurrentSnapshotData);

		/* Don't allow catalog snapshot to be older than xact snapshot. */
		CatalogSnapshotStale = true;

		FirstSnapshotSet = true;
		return CurrentSnapshot;
	}

	if (IsolationUsesXactSnapshot())
		return CurrentSnapshot;

	/* Don't allow catalog snapshot to be older than xact snapshot. */
	CatalogSnapshotStale = true;

	CurrentSnapshot = GetSnapshotData(&CurrentSnapshotData);

	return CurrentSnapshot;
}