head	1.4;
access;
symbols;
locks; strict;
comment	@ * @;


1.4
date	92.03.01.13.13.47;	author mao;	state Exp;
branches;
next	1.3;

1.3
date	91.05.05.19.45.03;	author mao;	state Exp;
branches;
next	1.2;

1.2
date	91.04.28.15.16.12;	author mao;	state Exp;
branches;
next	1.1;

1.1
date	91.04.27.12.10.01;	author mao;	state Exp;
branches;
next	;


desc
@scan synchronization code -- if we are doing a scan on a tree we're also
modifying, we need to be sure we don't lose our place in the scan.
@


1.4
log
@hack to fix memory management botch in inversion file system code --
turn off frees of small items in scan for testing.
@
text
@/*
 *  btscan.c -- manage scans on btrees.
 *
 *	Because we can be doing an index scan on a relation while we update
 *	it, we need to avoid missing data that moves around in the index.
 *	The routines and global variables in this file guarantee that all
 *	scans in the local address space stay correctly positioned.  This
 *	is all we need to worry about, since write locking guarantees that
 *	no one else will be on the same page at the same time as we are.
 *
 *	The scheme is to manage a list of active scans in the current backend.
 *	Whenever we add or remove records from an index, or whenever we
 *	split a leaf page, we check the list of active scans to see if any
 *	has been affected.  A scan is affected only if it is on the same
 *	relation, and the same page, as the update.
 */

#include "tmp/c.h"
#include "tmp/postgres.h"

#include "storage/bufmgr.h"
#include "storage/bufpage.h"
#include "storage/page.h"

#include "utils/log.h"
#include "utils/rel.h"
#include "utils/excid.h"

#include "access/heapam.h"
#include "access/genam.h"
#include "access/sdir.h"
#include "access/nbtree.h"

RcsId("$Header: RCS/nbtscan.c,v 1.3 91/05/05 19:45:03 mao Exp Locker: mao $");

typedef struct BTScanListData {
	IndexScanDesc		btsl_scan;
	struct BTScanListData	*btsl_next;
} BTScanListData;

typedef BTScanListData	*BTScanList;

static BTScanList	BTScans = (BTScanList) NULL;

/*
 *  _bt_regscan() -- register a new scan.
 */

void
_bt_regscan(scan)
    IndexScanDesc scan;
{
    BTScanList new_el;

    new_el = (BTScanList) palloc(sizeof(BTScanListData));
    new_el->btsl_scan = scan;
    new_el->btsl_next = BTScans;
    BTScans = new_el;
}

/*
 *  _bt_dropscan() -- drop a scan from the scan list
 */

void
_bt_dropscan(scan)
    IndexScanDesc scan;
{
    BTScanList chk, last;

    last = (BTScanList) NULL;
    for (chk = BTScans;
	 chk != (BTScanList) NULL && chk->btsl_scan != scan;
	 chk = chk->btsl_next) {
	last = chk;
    }

    if (chk == (BTScanList) NULL)
	elog(WARN, "btree scan list trashed; can't find 0x%lx", scan);

    if (last == (BTScanList) NULL)
	BTScans = chk->btsl_next;
    else
	last->btsl_next = chk->btsl_next;

#ifdef PERFECT_MEM
    pfree (chk);
#endif /* PERFECT_MEM */
}

void
_bt_adjscans(rel, tid)
    Relation rel;
    ItemPointer tid;
{
    BTScanList l;
    ObjectId relid, chkrelid;

    relid = rel->rd_id;
    for (l = BTScans; l != (BTScanList) NULL; l = l->btsl_next) {
	if (relid == l->btsl_scan->relation->rd_id)
	    _bt_scandel(l->btsl_scan, ItemPointerGetBlockNumber(tid),
			ItemPointerGetOffsetNumber(tid, 0));
    }
}

void
_bt_scandel(scan, blkno, offno)
    IndexScanDesc scan;
    BlockNumber blkno;
    OffsetNumber offno;
{
    ItemPointer current;
    Buffer buf;
    BTScanOpaque so;

    if (!_bt_scantouched(scan, blkno, offno))
	return;

    so = (BTScanOpaque) scan->opaque;
    buf = so->btso_curbuf;

    current = &(scan->currentItemData);
    if (ItemPointerIsValid(current)
	&& ItemPointerGetBlockNumber(current) == blkno
	&& ItemPointerGetOffsetNumber(current, 0) >= offno) {
	_bt_step(scan, &buf, BackwardScanDirection);
	so->btso_curbuf = buf;
    }

    current = &(scan->currentMarkData);
    if (ItemPointerIsValid(current)
	&& ItemPointerGetBlockNumber(current) == blkno
	&& ItemPointerGetOffsetNumber(current, 0) >= offno) {
	ItemPointerData tmp;
	tmp = *current;
	*current = scan->currentItemData;
	scan->currentItemData = tmp;
	_bt_step(scan, &buf, BackwardScanDirection);
	so->btso_mrkbuf = buf;
	tmp = *current;
	*current = scan->currentItemData;
	scan->currentItemData = tmp;
    }
}

bool
_bt_scantouched(scan, blkno, offno)
    IndexScanDesc scan;
    BlockNumber blkno;
    OffsetNumber offno;
{
    ItemPointer current;

    current = &(scan->currentItemData);
    if (ItemPointerIsValid(current)
	&& ItemPointerGetBlockNumber(current) == blkno
	&& ItemPointerGetOffsetNumber(current, 0) >= offno)
	return (true);

    current = &(scan->currentMarkData);
    if (ItemPointerIsValid(current)
	&& ItemPointerGetBlockNumber(current) == blkno
	&& ItemPointerGetOffsetNumber(current, 0) >= offno)
	return (true);

    return (false);
}
@


1.3
log
@fix deletion, scan management code due to vacuum cleaner testing
@
text
@d34 1
a34 1
RcsId("$Header: RCS/nbtscan.c,v 1.2 91/04/28 15:16:12 mao Exp Locker: mao $");
d86 1
d88 1
@


1.2
log
@get rid of BT_NONE accesses to pages; cache current, marked buffers for
scans to avoid unnecessary semop() calls; fix buffer leak reported by
wei (equality joins that failed used to not unpin buffers).
@
text
@d34 1
a34 1
RcsId("$Header: RCS/nbtscan.c,v 1.1 91/04/27 12:10:01 mao Exp Locker: mao $");
d106 1
a106 1
_bt_scandel(scan, blkno, offind)
d109 1
a109 1
    OffsetIndex offind;
a112 2
    Page page;
    OffsetIndex maxoff;
d115 1
a115 1
    if (!_bt_scantouched(scan, blkno, offind))
a119 2
    page = BufferGetPage(buf, 0);
    maxoff = PageGetMaxOffsetIndex(page);
d124 1
a124 1
	&& ItemPointerGetOffsetNumber(current, 0) >= offind + 1) {
d132 1
a132 1
	&& ItemPointerGetOffsetNumber(current, 0) >= offind + 1) {
d146 1
a146 1
_bt_scantouched(scan, blkno, offind)
d149 1
a149 1
    OffsetIndex offind;
d156 1
a156 1
	&& ItemPointerGetOffsetNumber(current, 0) >= offind + 1)
d162 1
a162 1
	&& ItemPointerGetOffsetNumber(current, 0) >= offind + 1)
@


1.1
log
@Initial revision
@
text
@d34 1
a34 1
RcsId("$Header$");
d43 1
a43 1
BTScanList	BTScans = (BTScanList) NULL;
d115 1
d120 2
a121 1
    buf = _bt_getbuf(scan->relation, blkno, BT_NONE);
d129 2
a130 1
	_bt_step(scan, BackwardScanDirection);
d141 2
a142 1
	_bt_step(scan, BackwardScanDirection);
a146 1
    _bt_relbuf(scan->relation, buf, BT_NONE);
@