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/*-------------------------------------------------------------------------
*
* hio.c
* POSTGRES heap access method input/output code.
*
* Portions Copyright (c) 1996-2000, PostgreSQL, Inc
* Portions Copyright (c) 1994, Regents of the University of California
*
*
* IDENTIFICATION
* $Id: hio.c,v 1.31 2000/04/12 17:14:45 momjian Exp $
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "access/heapam.h"
#include "access/hio.h"
/*
* amputunique - place tuple at tid
* Currently on errors, calls elog. Perhaps should return -1?
* Possible errors include the addition of a tuple to the page
* between the time the linep is chosen and the page is L_UP'd.
*
* This should be coordinated with the B-tree code.
* Probably needs to have an amdelunique to allow for
* internal index records to be deleted and reordered as needed.
* For the heap AM, this should never be needed.
*
* Note - we assume that caller hold BUFFER_LOCK_EXCLUSIVE on the buffer.
*
*/
void
RelationPutHeapTuple(Relation relation,
Buffer buffer,
HeapTuple tuple)
{
Page pageHeader;
OffsetNumber offnum;
Size len;
ItemId itemId;
Item item;
/* ----------------
* increment access statistics
* ----------------
*/
IncrHeapAccessStat(local_RelationPutHeapTuple);
IncrHeapAccessStat(global_RelationPutHeapTuple);
pageHeader = (Page) BufferGetPage(buffer);
len = MAXALIGN(tuple->t_len); /* be conservative */
Assert(len <= PageGetFreeSpace(pageHeader));
offnum = PageAddItem((Page) pageHeader, (Item) tuple->t_data,
tuple->t_len, InvalidOffsetNumber, LP_USED);
itemId = PageGetItemId((Page) pageHeader, offnum);
item = PageGetItem((Page) pageHeader, itemId);
ItemPointerSet(&((HeapTupleHeader) item)->t_ctid,
BufferGetBlockNumber(buffer), offnum);
/*
* Let the caller do this!
*
* WriteBuffer(buffer);
*/
/* return an accurate tuple */
ItemPointerSet(&tuple->t_self, BufferGetBlockNumber(buffer), offnum);
}
/*
* This routine is another in the series of attempts to reduce the number
* of I/O's and system calls executed in the various benchmarks. In
* particular, this routine is used to append data to the end of a relation
* file without excessive lseeks. This code should do no more than 2 semops
* in the ideal case.
*
* Eventually, we should cache the number of blocks in a relation somewhere.
* Until that time, this code will have to do an lseek to determine the number
* of blocks in a relation.
*
* This code should ideally do at most 4 semops, 1 lseek, and possibly 1 write
* to do an append; it's possible to eliminate 2 of the semops if we do direct
* buffer stuff (!); the lseek and the write can go if we get
* RelationGetNumberOfBlocks to be useful.
*
* NOTE: This code presumes that we have a write lock on the relation.
* Not now - we use extend locking...
*
* Also note that this routine probably shouldn't have to exist, and does
* screw up the call graph rather badly, but we are wasting so much time and
* system resources being massively general that we are losing badly in our
* performance benchmarks.
*/
void
RelationPutHeapTupleAtEnd(Relation relation, HeapTuple tuple)
{
Buffer buffer;
Page pageHeader;
BlockNumber lastblock;
OffsetNumber offnum;
Size len;
ItemId itemId;
Item item;
len = MAXALIGN(tuple->t_len); /* be conservative */
/*
* If we're gonna fail for oversize tuple, do it right away... this
* code should go away eventually.
*/
if (len > MaxTupleSize)
elog(ERROR, "Tuple is too big: size %u, max size %ld",
len, MaxTupleSize);
/*
* Lock relation for extension. We can use LockPage here as long as in
* all other places we use page-level locking for indices only.
* Alternatively, we could define pseudo-table as we do for
* transactions with XactLockTable.
*/
if (!relation->rd_myxactonly)
LockPage(relation, 0, ExclusiveLock);
/*
* XXX This does an lseek - VERY expensive - but at the moment it is
* the only way to accurately determine how many blocks are in a
* relation. A good optimization would be to get this to actually
* work properly.
*/
lastblock = RelationGetNumberOfBlocks(relation);
/*
* Get the last existing page --- may need to create the first one if
* this is a virgin relation.
*/
if (lastblock == 0)
{
/* what exactly is this all about??? */
buffer = ReadBuffer(relation, lastblock);
pageHeader = (Page) BufferGetPage(buffer);
Assert(PageIsNew((PageHeader) pageHeader));
buffer = ReleaseAndReadBuffer(buffer, relation, P_NEW);
pageHeader = (Page) BufferGetPage(buffer);
PageInit(pageHeader, BufferGetPageSize(buffer), 0);
}
else
buffer = ReadBuffer(relation, lastblock - 1);
LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
pageHeader = (Page) BufferGetPage(buffer);
/*
* Is there room on the last existing page?
*/
if (len > PageGetFreeSpace(pageHeader))
{
LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
buffer = ReleaseAndReadBuffer(buffer, relation, P_NEW);
LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
pageHeader = (Page) BufferGetPage(buffer);
PageInit(pageHeader, BufferGetPageSize(buffer), 0);
if (len > PageGetFreeSpace(pageHeader))
{
/*
* BUG: by elog'ing here, we leave the new buffer locked and
* not marked dirty, which may result in an invalid page
* header being left on disk. But we should not get here
* given the test at the top of the routine, and the whole
* deal should go away when we implement tuple splitting
* anyway...
*/
elog(ERROR, "Tuple is too big: size %u", len);
}
}
if (!relation->rd_myxactonly)
UnlockPage(relation, 0, ExclusiveLock);
offnum = PageAddItem((Page) pageHeader, (Item) tuple->t_data,
tuple->t_len, InvalidOffsetNumber, LP_USED);
itemId = PageGetItemId((Page) pageHeader, offnum);
item = PageGetItem((Page) pageHeader, itemId);
lastblock = BufferGetBlockNumber(buffer);
ItemPointerSet(&((HeapTupleHeader) item)->t_ctid, lastblock, offnum);
/* return an accurate tuple self-pointer */
ItemPointerSet(&tuple->t_self, lastblock, offnum);
LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
WriteBuffer(buffer);
}
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