Fix xslt_process() to ensure that it inserts a NULL terminator after the

[PostgreSQL.git] / src / backend / access / heap / hio.c

/*-------------------------------------------------------------------------
 *
 * hio.c
 *        POSTGRES heap access method input/output code.
 *
 * Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *        $PostgreSQL$
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include "access/heapam.h"
#include "access/hio.h"
#include "storage/bufmgr.h"
#include "storage/freespace.h"
#include "storage/lmgr.h"


/*
 * RelationPutHeapTuple - place tuple at specified page
 *
 * !!! EREPORT(ERROR) IS DISALLOWED HERE !!!  Must PANIC on failure!!!
 *
 * Note - caller must hold BUFFER_LOCK_EXCLUSIVE on the buffer.
 */
void
RelationPutHeapTuple(Relation relation,
                                         Buffer buffer,
                                         HeapTuple tuple)
{
        Page            pageHeader;
        OffsetNumber offnum;
        ItemId          itemId;
        Item            item;

        /* Add the tuple to the page */
        pageHeader = BufferGetPage(buffer);

        offnum = PageAddItem(pageHeader, (Item) tuple->t_data,
                                                 tuple->t_len, InvalidOffsetNumber, false, true);

        if (offnum == InvalidOffsetNumber)
                elog(PANIC, "failed to add tuple to page");

        /* Update tuple->t_self to the actual position where it was stored */
        ItemPointerSet(&(tuple->t_self), BufferGetBlockNumber(buffer), offnum);

        /* Insert the correct position into CTID of the stored tuple, too */
        itemId = PageGetItemId(pageHeader, offnum);
        item = PageGetItem(pageHeader, itemId);
        ((HeapTupleHeader) item)->t_ctid = tuple->t_self;
}

/*
 * Read in a buffer, using bulk-insert strategy if bistate isn't NULL.
 */
static Buffer
ReadBufferBI(Relation relation, BlockNumber targetBlock,
                         BulkInsertState bistate)
{
        Buffer          buffer;

        /* If not bulk-insert, exactly like ReadBuffer */
        if (!bistate)
                return ReadBuffer(relation, targetBlock);

        /* If we have the desired block already pinned, re-pin and return it */
        if (bistate->current_buf != InvalidBuffer)
        {
                if (BufferGetBlockNumber(bistate->current_buf) == targetBlock)
                {
                        IncrBufferRefCount(bistate->current_buf);
                        return bistate->current_buf;
                }
                /* ... else drop the old buffer */
                ReleaseBuffer(bistate->current_buf);
                bistate->current_buf = InvalidBuffer;
        }

        /* Perform a read using the buffer strategy */
        buffer = ReadBufferExtended(relation, MAIN_FORKNUM, targetBlock,
                                                                RBM_NORMAL, bistate->strategy);

        /* Save the selected block as target for future inserts */
        IncrBufferRefCount(buffer);
        bistate->current_buf = buffer;

        return buffer;
}

/*
 * RelationGetBufferForTuple
 *
 *      Returns pinned and exclusive-locked buffer of a page in given relation
 *      with free space >= given len.
 *
 *      If otherBuffer is not InvalidBuffer, then it references a previously
 *      pinned buffer of another page in the same relation; on return, this
 *      buffer will also be exclusive-locked.  (This case is used by heap_update;
 *      the otherBuffer contains the tuple being updated.)
 *
 *      The reason for passing otherBuffer is that if two backends are doing
 *      concurrent heap_update operations, a deadlock could occur if they try
 *      to lock the same two buffers in opposite orders.  To ensure that this
 *      can't happen, we impose the rule that buffers of a relation must be
 *      locked in increasing page number order.  This is most conveniently done
 *      by having RelationGetBufferForTuple lock them both, with suitable care
 *      for ordering.
 *
 *      NOTE: it is unlikely, but not quite impossible, for otherBuffer to be the
 *      same buffer we select for insertion of the new tuple (this could only
 *      happen if space is freed in that page after heap_update finds there's not
 *      enough there).  In that case, the page will be pinned and locked only once.
 *
 *      We normally use FSM to help us find free space.  However,
 *      if HEAP_INSERT_SKIP_FSM is specified, we just append a new empty page to
 *      the end of the relation if the tuple won't fit on the current target page.
 *      This can save some cycles when we know the relation is new and doesn't
 *      contain useful amounts of free space.
 *
 *      HEAP_INSERT_SKIP_FSM is also useful for non-WAL-logged additions to a
 *      relation, if the caller holds exclusive lock and is careful to invalidate
 *      relation->rd_targblock before the first insertion --- that ensures that
 *      all insertions will occur into newly added pages and not be intermixed
 *      with tuples from other transactions.  That way, a crash can't risk losing
 *      any committed data of other transactions.  (See heap_insert's comments
 *      for additional constraints needed for safe usage of this behavior.)
 *
 *      The caller can also provide a BulkInsertState object to optimize many
 *      insertions into the same relation.      This keeps a pin on the current
 *      insertion target page (to save pin/unpin cycles) and also passes a
 *      BULKWRITE buffer selection strategy object to the buffer manager.
 *      Passing NULL for bistate selects the default behavior.
 *
 *      We always try to avoid filling existing pages further than the fillfactor.
 *      This is OK since this routine is not consulted when updating a tuple and
 *      keeping it on the same page, which is the scenario fillfactor is meant
 *      to reserve space for.
 *
 *      ereport(ERROR) is allowed here, so this routine *must* be called
 *      before any (unlogged) changes are made in buffer pool.
 */
Buffer
RelationGetBufferForTuple(Relation relation, Size len,
                                                  Buffer otherBuffer, int options,
                                                  struct BulkInsertStateData *bistate)
{
        bool            use_fsm = !(options & HEAP_INSERT_SKIP_FSM);
        Buffer          buffer = InvalidBuffer;
        Page            page;
        Size            pageFreeSpace,
                                saveFreeSpace;
        BlockNumber targetBlock,
                                otherBlock;
        bool            needLock;

        len = MAXALIGN(len);            /* be conservative */

        /* Bulk insert is not supported for updates, only inserts. */
        Assert(otherBuffer == InvalidBuffer || !bistate);

        /*
         * If we're gonna fail for oversize tuple, do it right away
         */
        if (len > MaxHeapTupleSize)
                ereport(ERROR,
                                (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
                                 errmsg("row is too big: size %lu, maximum size %lu",
                                                (unsigned long) len,
                                                (unsigned long) MaxHeapTupleSize)));

        /* Compute desired extra freespace due to fillfactor option */
        saveFreeSpace = RelationGetTargetPageFreeSpace(relation,
                                                                                                   HEAP_DEFAULT_FILLFACTOR);

        if (otherBuffer != InvalidBuffer)
                otherBlock = BufferGetBlockNumber(otherBuffer);
        else
                otherBlock = InvalidBlockNumber;                /* just to keep compiler quiet */

        /*
         * We first try to put the tuple on the same page we last inserted a tuple
         * on, as cached in the BulkInsertState or relcache entry.      If that
         * doesn't work, we ask the Free Space Map to locate a suitable page.
         * Since the FSM's info might be out of date, we have to be prepared to
         * loop around and retry multiple times. (To insure this isn't an infinite
         * loop, we must update the FSM with the correct amount of free space on
         * each page that proves not to be suitable.)  If the FSM has no record of
         * a page with enough free space, we give up and extend the relation.
         *
         * When use_fsm is false, we either put the tuple onto the existing target
         * page or extend the relation.
         */
        if (len + saveFreeSpace > MaxHeapTupleSize)
        {
                /* can't fit, don't bother asking FSM */
                targetBlock = InvalidBlockNumber;
                use_fsm = false;
        }
        else if (bistate && bistate->current_buf != InvalidBuffer)
                targetBlock = BufferGetBlockNumber(bistate->current_buf);
        else
                targetBlock = relation->rd_targblock;

        if (targetBlock == InvalidBlockNumber && use_fsm)
        {
                /*
                 * We have no cached target page, so ask the FSM for an initial
                 * target.
                 */
                targetBlock = GetPageWithFreeSpace(relation, len + saveFreeSpace);

                /*
                 * If the FSM knows nothing of the rel, try the last page before we
                 * give up and extend.  This avoids one-tuple-per-page syndrome during
                 * bootstrapping or in a recently-started system.
                 */
                if (targetBlock == InvalidBlockNumber)
                {
                        BlockNumber nblocks = RelationGetNumberOfBlocks(relation);

                        if (nblocks > 0)
                                targetBlock = nblocks - 1;
                }
        }

        while (targetBlock != InvalidBlockNumber)
        {
                /*
                 * Read and exclusive-lock the target block, as well as the other
                 * block if one was given, taking suitable care with lock ordering and
                 * the possibility they are the same block.
                 */
                if (otherBuffer == InvalidBuffer)
                {
                        /* easy case */
                        buffer = ReadBufferBI(relation, targetBlock, bistate);
                        LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
                }
                else if (otherBlock == targetBlock)
                {
                        /* also easy case */
                        buffer = otherBuffer;
                        LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
                }
                else if (otherBlock < targetBlock)
                {
                        /* lock other buffer first */
                        buffer = ReadBuffer(relation, targetBlock);
                        LockBuffer(otherBuffer, BUFFER_LOCK_EXCLUSIVE);
                        LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
                }
                else
                {
                        /* lock target buffer first */
                        buffer = ReadBuffer(relation, targetBlock);
                        LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
                        LockBuffer(otherBuffer, BUFFER_LOCK_EXCLUSIVE);
                }

                /*
                 * Now we can check to see if there's enough free space here. If so,
                 * we're done.
                 */
                page = BufferGetPage(buffer);
                pageFreeSpace = PageGetHeapFreeSpace(page);
                if (len + saveFreeSpace <= pageFreeSpace)
                {
                        /* use this page as future insert target, too */
                        relation->rd_targblock = targetBlock;
                        return buffer;
                }

                /*
                 * Not enough space, so we must give up our page locks and pin (if
                 * any) and prepare to look elsewhere.  We don't care which order we
                 * unlock the two buffers in, so this can be slightly simpler than the
                 * code above.
                 */
                LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
                if (otherBuffer == InvalidBuffer)
                        ReleaseBuffer(buffer);
                else if (otherBlock != targetBlock)
                {
                        LockBuffer(otherBuffer, BUFFER_LOCK_UNLOCK);
                        ReleaseBuffer(buffer);
                }

                /* Without FSM, always fall out of the loop and extend */
                if (!use_fsm)
                        break;

                /*
                 * Update FSM as to condition of this page, and ask for another page
                 * to try.
                 */
                targetBlock = RecordAndGetPageWithFreeSpace(relation,
                                                                                                        targetBlock,
                                                                                                        pageFreeSpace,
                                                                                                        len + saveFreeSpace);
        }

        /*
         * Have to extend the relation.
         *
         * We have to use a lock to ensure no one else is extending the rel at the
         * same time, else we will both try to initialize the same new page.  We
         * can skip locking for new or temp relations, however, since no one else
         * could be accessing them.
         */
        needLock = !RELATION_IS_LOCAL(relation);

        if (needLock)
                LockRelationForExtension(relation, ExclusiveLock);

        /*
         * XXX This does an lseek - rather expensive - but at the moment it is the
         * only way to accurately determine how many blocks are in a relation.  Is
         * it worth keeping an accurate file length in shared memory someplace,
         * rather than relying on the kernel to do it for us?
         */
        buffer = ReadBufferBI(relation, P_NEW, bistate);

        /*
         * We can be certain that locking the otherBuffer first is OK, since it
         * must have a lower page number.
         */
        if (otherBuffer != InvalidBuffer)
                LockBuffer(otherBuffer, BUFFER_LOCK_EXCLUSIVE);

        /*
         * Now acquire lock on the new page.
         */
        LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);

        /*
         * Release the file-extension lock; it's now OK for someone else to extend
         * the relation some more.      Note that we cannot release this lock before
         * we have buffer lock on the new page, or we risk a race condition
         * against vacuumlazy.c --- see comments therein.
         */
        if (needLock)
                UnlockRelationForExtension(relation, ExclusiveLock);

        /*
         * We need to initialize the empty new page.  Double-check that it really
         * is empty (this should never happen, but if it does we don't want to
         * risk wiping out valid data).
         */
        page = BufferGetPage(buffer);

        if (!PageIsNew(page))
                elog(ERROR, "page %u of relation \"%s\" should be empty but is not",
                         BufferGetBlockNumber(buffer),
                         RelationGetRelationName(relation));

        PageInit(page, BufferGetPageSize(buffer), 0);

        if (len > PageGetHeapFreeSpace(page))
        {
                /* We should not get here given the test at the top */
                elog(PANIC, "tuple is too big: size %lu", (unsigned long) len);
        }

        /*
         * Remember the new page as our target for future insertions.
         *
         * XXX should we enter the new page into the free space map immediately,
         * or just keep it for this backend's exclusive use in the short run
         * (until VACUUM sees it)?      Seems to depend on whether you expect the
         * current backend to make more insertions or not, which is probably a
         * good bet most of the time.  So for now, don't add it to FSM yet.
         */
        relation->rd_targblock = BufferGetBlockNumber(buffer);

        return buffer;
}