mirror of
https://git.postgresql.org/git/postgresql.git
synced 2024-09-28 09:11:50 +02:00
443 lines
12 KiB
C
443 lines
12 KiB
C
/*-------------------------------------------------------------------------
|
|
*
|
|
* nbtpage.c
|
|
* BTree-specific page management code for the Postgres btree access
|
|
* method.
|
|
*
|
|
* Portions Copyright (c) 1996-2001, PostgreSQL Global Development Group
|
|
* Portions Copyright (c) 1994, Regents of the University of California
|
|
*
|
|
*
|
|
* IDENTIFICATION
|
|
* $Header: /cvsroot/pgsql/src/backend/access/nbtree/nbtpage.c,v 1.47 2001/01/24 19:42:48 momjian Exp $
|
|
*
|
|
* NOTES
|
|
* Postgres btree pages look like ordinary relation pages. The opaque
|
|
* data at high addresses includes pointers to left and right siblings
|
|
* and flag data describing page state. The first page in a btree, page
|
|
* zero, is special -- it stores meta-information describing the tree.
|
|
* Pages one and higher store the actual tree data.
|
|
*
|
|
*-------------------------------------------------------------------------
|
|
*/
|
|
#include "postgres.h"
|
|
|
|
#include <time.h>
|
|
|
|
#include "access/nbtree.h"
|
|
#include "miscadmin.h"
|
|
#include "storage/lmgr.h"
|
|
|
|
|
|
/*
|
|
* We use high-concurrency locking on btrees. There are two cases in
|
|
* which we don't do locking. One is when we're building the btree.
|
|
* Since the creating transaction has not committed, no one can see
|
|
* the index, and there's no reason to share locks. The second case
|
|
* is when we're just starting up the database system. We use some
|
|
* special-purpose initialization code in the relation cache manager
|
|
* (see utils/cache/relcache.c) to allow us to do indexed scans on
|
|
* the system catalogs before we'd normally be able to. This happens
|
|
* before the lock table is fully initialized, so we can't use it.
|
|
* Strictly speaking, this violates 2pl, but we don't do 2pl on the
|
|
* system catalogs anyway, so I declare this to be okay.
|
|
*/
|
|
|
|
#define USELOCKING (!BuildingBtree && !IsInitProcessingMode())
|
|
|
|
/*
|
|
* _bt_metapinit() -- Initialize the metadata page of a btree.
|
|
*/
|
|
void
|
|
_bt_metapinit(Relation rel)
|
|
{
|
|
Buffer buf;
|
|
Page pg;
|
|
int nblocks;
|
|
BTMetaPageData metad;
|
|
BTPageOpaque op;
|
|
|
|
/* can't be sharing this with anyone, now... */
|
|
if (USELOCKING)
|
|
LockRelation(rel, AccessExclusiveLock);
|
|
|
|
if ((nblocks = RelationGetNumberOfBlocks(rel)) != 0)
|
|
{
|
|
elog(ERROR, "Cannot initialize non-empty btree %s",
|
|
RelationGetRelationName(rel));
|
|
}
|
|
|
|
buf = ReadBuffer(rel, P_NEW);
|
|
pg = BufferGetPage(buf);
|
|
_bt_pageinit(pg, BufferGetPageSize(buf));
|
|
|
|
metad.btm_magic = BTREE_MAGIC;
|
|
metad.btm_version = BTREE_VERSION;
|
|
metad.btm_root = P_NONE;
|
|
metad.btm_level = 0;
|
|
memcpy((char *) BTPageGetMeta(pg), (char *) &metad, sizeof(metad));
|
|
|
|
op = (BTPageOpaque) PageGetSpecialPointer(pg);
|
|
op->btpo_flags = BTP_META;
|
|
|
|
WriteBuffer(buf);
|
|
|
|
/* all done */
|
|
if (USELOCKING)
|
|
UnlockRelation(rel, AccessExclusiveLock);
|
|
}
|
|
|
|
/*
|
|
* _bt_getroot() -- Get the root page of the btree.
|
|
*
|
|
* Since the root page can move around the btree file, we have to read
|
|
* its location from the metadata page, and then read the root page
|
|
* itself. If no root page exists yet, we have to create one. The
|
|
* standard class of race conditions exists here; I think I covered
|
|
* them all in the Hopi Indian rain dance of lock requests below.
|
|
*
|
|
* The access type parameter (BT_READ or BT_WRITE) controls whether
|
|
* a new root page will be created or not. If access = BT_READ,
|
|
* and no root page exists, we just return InvalidBuffer. For
|
|
* BT_WRITE, we try to create the root page if it doesn't exist.
|
|
* NOTE that the returned root page will have only a read lock set
|
|
* on it even if access = BT_WRITE!
|
|
*
|
|
* On successful return, the root page is pinned and read-locked.
|
|
* The metadata page is not locked or pinned on exit.
|
|
*/
|
|
Buffer
|
|
_bt_getroot(Relation rel, int access)
|
|
{
|
|
Buffer metabuf;
|
|
Page metapg;
|
|
BTPageOpaque metaopaque;
|
|
Buffer rootbuf;
|
|
Page rootpage;
|
|
BTPageOpaque rootopaque;
|
|
BlockNumber rootblkno;
|
|
BTMetaPageData *metad;
|
|
|
|
metabuf = _bt_getbuf(rel, BTREE_METAPAGE, BT_READ);
|
|
metapg = BufferGetPage(metabuf);
|
|
metaopaque = (BTPageOpaque) PageGetSpecialPointer(metapg);
|
|
metad = BTPageGetMeta(metapg);
|
|
|
|
if (!(metaopaque->btpo_flags & BTP_META) ||
|
|
metad->btm_magic != BTREE_MAGIC)
|
|
elog(ERROR, "Index %s is not a btree",
|
|
RelationGetRelationName(rel));
|
|
|
|
if (metad->btm_version != BTREE_VERSION)
|
|
elog(ERROR, "Version mismatch on %s: version %d file, version %d code",
|
|
RelationGetRelationName(rel),
|
|
metad->btm_version, BTREE_VERSION);
|
|
|
|
/* if no root page initialized yet, do it */
|
|
if (metad->btm_root == P_NONE)
|
|
{
|
|
/* If access = BT_READ, caller doesn't want us to create root yet */
|
|
if (access == BT_READ)
|
|
{
|
|
_bt_relbuf(rel, metabuf, BT_READ);
|
|
return InvalidBuffer;
|
|
}
|
|
|
|
/* trade in our read lock for a write lock */
|
|
LockBuffer(metabuf, BUFFER_LOCK_UNLOCK);
|
|
LockBuffer(metabuf, BT_WRITE);
|
|
|
|
/*
|
|
* Race condition: if someone else initialized the metadata
|
|
* between the time we released the read lock and acquired the
|
|
* write lock, above, we must avoid doing it again.
|
|
*/
|
|
if (metad->btm_root == P_NONE)
|
|
{
|
|
|
|
/*
|
|
* Get, initialize, write, and leave a lock of the appropriate
|
|
* type on the new root page. Since this is the first page in
|
|
* the tree, it's a leaf as well as the root.
|
|
*/
|
|
rootbuf = _bt_getbuf(rel, P_NEW, BT_WRITE);
|
|
rootblkno = BufferGetBlockNumber(rootbuf);
|
|
rootpage = BufferGetPage(rootbuf);
|
|
|
|
/* NO ELOG(ERROR) till meta is updated */
|
|
START_CRIT_SECTION();
|
|
|
|
metad->btm_root = rootblkno;
|
|
metad->btm_level = 1;
|
|
|
|
_bt_pageinit(rootpage, BufferGetPageSize(rootbuf));
|
|
rootopaque = (BTPageOpaque) PageGetSpecialPointer(rootpage);
|
|
rootopaque->btpo_flags |= (BTP_LEAF | BTP_ROOT);
|
|
|
|
/* XLOG stuff */
|
|
{
|
|
xl_btree_newroot xlrec;
|
|
XLogRecPtr recptr;
|
|
XLogRecData rdata;
|
|
|
|
xlrec.node = rel->rd_node;
|
|
xlrec.level = 1;
|
|
BlockIdSet(&(xlrec.rootblk), rootblkno);
|
|
rdata.buffer = InvalidBuffer;
|
|
rdata.data = (char*)&xlrec;
|
|
rdata.len = SizeOfBtreeNewroot;
|
|
rdata.next = NULL;
|
|
|
|
recptr = XLogInsert(RM_BTREE_ID,
|
|
XLOG_BTREE_NEWROOT|XLOG_BTREE_LEAF, &rdata);
|
|
|
|
PageSetLSN(rootpage, recptr);
|
|
PageSetSUI(rootpage, ThisStartUpID);
|
|
PageSetLSN(metapg, recptr);
|
|
PageSetSUI(metapg, ThisStartUpID);
|
|
}
|
|
|
|
END_CRIT_SECTION();
|
|
|
|
_bt_wrtnorelbuf(rel, rootbuf);
|
|
|
|
/* swap write lock for read lock */
|
|
LockBuffer(rootbuf, BUFFER_LOCK_UNLOCK);
|
|
LockBuffer(rootbuf, BT_READ);
|
|
|
|
/* okay, metadata is correct, write and release it */
|
|
_bt_wrtbuf(rel, metabuf);
|
|
}
|
|
else
|
|
{
|
|
/*
|
|
* Metadata initialized by someone else. In order to
|
|
* guarantee no deadlocks, we have to release the metadata
|
|
* page and start all over again.
|
|
*/
|
|
_bt_relbuf(rel, metabuf, BT_WRITE);
|
|
return _bt_getroot(rel, access);
|
|
}
|
|
}
|
|
else
|
|
{
|
|
rootblkno = metad->btm_root;
|
|
_bt_relbuf(rel, metabuf, BT_READ); /* done with the meta page */
|
|
|
|
rootbuf = _bt_getbuf(rel, rootblkno, BT_READ);
|
|
}
|
|
|
|
/*
|
|
* Race condition: If the root page split between the time we looked
|
|
* at the metadata page and got the root buffer, then we got the wrong
|
|
* buffer. Release it and try again.
|
|
*/
|
|
rootpage = BufferGetPage(rootbuf);
|
|
rootopaque = (BTPageOpaque) PageGetSpecialPointer(rootpage);
|
|
|
|
if (! P_ISROOT(rootopaque))
|
|
{
|
|
/* it happened, try again */
|
|
_bt_relbuf(rel, rootbuf, BT_READ);
|
|
return _bt_getroot(rel, access);
|
|
}
|
|
|
|
/*
|
|
* By here, we have a correct lock on the root block, its reference
|
|
* count is correct, and we have no lock set on the metadata page.
|
|
* Return the root block.
|
|
*/
|
|
return rootbuf;
|
|
}
|
|
|
|
/*
|
|
* _bt_getbuf() -- Get a buffer by block number for read or write.
|
|
*
|
|
* When this routine returns, the appropriate lock is set on the
|
|
* requested buffer and its reference count has been incremented
|
|
* (ie, the buffer is "locked and pinned").
|
|
*/
|
|
Buffer
|
|
_bt_getbuf(Relation rel, BlockNumber blkno, int access)
|
|
{
|
|
Buffer buf;
|
|
|
|
if (blkno != P_NEW)
|
|
{
|
|
/* Read an existing block of the relation */
|
|
buf = ReadBuffer(rel, blkno);
|
|
LockBuffer(buf, access);
|
|
}
|
|
else
|
|
{
|
|
Page page;
|
|
|
|
/*
|
|
* Extend the relation by one page.
|
|
*
|
|
* Extend bufmgr code is unclean and so we have to use extra locking
|
|
* here.
|
|
*/
|
|
LockPage(rel, 0, ExclusiveLock);
|
|
buf = ReadBuffer(rel, blkno);
|
|
LockBuffer(buf, access);
|
|
UnlockPage(rel, 0, ExclusiveLock);
|
|
|
|
/* Initialize the new page before returning it */
|
|
page = BufferGetPage(buf);
|
|
_bt_pageinit(page, BufferGetPageSize(buf));
|
|
}
|
|
|
|
/* ref count and lock type are correct */
|
|
return buf;
|
|
}
|
|
|
|
/*
|
|
* _bt_relbuf() -- release a locked buffer.
|
|
*
|
|
* Lock and pin (refcount) are both dropped.
|
|
*/
|
|
void
|
|
_bt_relbuf(Relation rel, Buffer buf, int access)
|
|
{
|
|
LockBuffer(buf, BUFFER_LOCK_UNLOCK);
|
|
ReleaseBuffer(buf);
|
|
}
|
|
|
|
/*
|
|
* _bt_wrtbuf() -- write a btree page to disk.
|
|
*
|
|
* This routine releases the lock held on the buffer and our refcount
|
|
* for it. It is an error to call _bt_wrtbuf() without a write lock
|
|
* and a pin on the buffer.
|
|
*
|
|
* NOTE: actually, the buffer manager just marks the shared buffer page
|
|
* dirty here, the real I/O happens later. Since we can't persuade the
|
|
* Unix kernel to schedule disk writes in a particular order, there's not
|
|
* much point in worrying about this. The most we can say is that all the
|
|
* writes will occur before commit.
|
|
*/
|
|
void
|
|
_bt_wrtbuf(Relation rel, Buffer buf)
|
|
{
|
|
LockBuffer(buf, BUFFER_LOCK_UNLOCK);
|
|
WriteBuffer(buf);
|
|
}
|
|
|
|
/*
|
|
* _bt_wrtnorelbuf() -- write a btree page to disk, but do not release
|
|
* our reference or lock.
|
|
*
|
|
* It is an error to call _bt_wrtnorelbuf() without a write lock
|
|
* and a pin on the buffer.
|
|
*
|
|
* See above NOTE.
|
|
*/
|
|
void
|
|
_bt_wrtnorelbuf(Relation rel, Buffer buf)
|
|
{
|
|
WriteNoReleaseBuffer(buf);
|
|
}
|
|
|
|
/*
|
|
* _bt_pageinit() -- Initialize a new page.
|
|
*/
|
|
void
|
|
_bt_pageinit(Page page, Size size)
|
|
{
|
|
|
|
/*
|
|
* Cargo_cult programming -- don't really need this to be zero, but
|
|
* creating new pages is an infrequent occurrence and it makes me feel
|
|
* good when I know they're empty.
|
|
*/
|
|
|
|
MemSet(page, 0, size);
|
|
|
|
PageInit(page, size, sizeof(BTPageOpaqueData));
|
|
((BTPageOpaque) PageGetSpecialPointer(page))->btpo_parent =
|
|
InvalidBlockNumber;
|
|
}
|
|
|
|
/*
|
|
* _bt_metaproot() -- Change the root page of the btree.
|
|
*
|
|
* Lehman and Yao require that the root page move around in order to
|
|
* guarantee deadlock-free short-term, fine-granularity locking. When
|
|
* we split the root page, we record the new parent in the metadata page
|
|
* for the relation. This routine does the work.
|
|
*
|
|
* No direct preconditions, but if you don't have the write lock on
|
|
* at least the old root page when you call this, you're making a big
|
|
* mistake. On exit, metapage data is correct and we no longer have
|
|
* a pin or lock on the metapage.
|
|
*/
|
|
void
|
|
_bt_metaproot(Relation rel, BlockNumber rootbknum, int level)
|
|
{
|
|
Buffer metabuf;
|
|
Page metap;
|
|
BTPageOpaque metaopaque;
|
|
BTMetaPageData *metad;
|
|
|
|
metabuf = _bt_getbuf(rel, BTREE_METAPAGE, BT_WRITE);
|
|
metap = BufferGetPage(metabuf);
|
|
metaopaque = (BTPageOpaque) PageGetSpecialPointer(metap);
|
|
Assert(metaopaque->btpo_flags & BTP_META);
|
|
metad = BTPageGetMeta(metap);
|
|
metad->btm_root = rootbknum;
|
|
if (level == 0) /* called from _do_insert */
|
|
metad->btm_level += 1;
|
|
else
|
|
metad->btm_level = level; /* called from btsort */
|
|
_bt_wrtbuf(rel, metabuf);
|
|
}
|
|
|
|
/*
|
|
* Delete an item from a btree. It had better be a leaf item...
|
|
*/
|
|
void
|
|
_bt_pagedel(Relation rel, ItemPointer tid)
|
|
{
|
|
Buffer buf;
|
|
Page page;
|
|
BlockNumber blkno;
|
|
OffsetNumber offno;
|
|
|
|
blkno = ItemPointerGetBlockNumber(tid);
|
|
offno = ItemPointerGetOffsetNumber(tid);
|
|
|
|
buf = _bt_getbuf(rel, blkno, BT_WRITE);
|
|
page = BufferGetPage(buf);
|
|
|
|
START_CRIT_SECTION();
|
|
PageIndexTupleDelete(page, offno);
|
|
/* XLOG stuff */
|
|
{
|
|
xl_btree_delete xlrec;
|
|
XLogRecPtr recptr;
|
|
XLogRecData rdata[2];
|
|
|
|
xlrec.target.node = rel->rd_node;
|
|
xlrec.target.tid = *tid;
|
|
rdata[0].buffer = InvalidBuffer;
|
|
rdata[0].data = (char*)&xlrec;
|
|
rdata[0].len = SizeOfBtreeDelete;
|
|
rdata[0].next = &(rdata[1]);
|
|
|
|
rdata[1].buffer = buf;
|
|
rdata[1].data = NULL;
|
|
rdata[1].len = 0;
|
|
rdata[1].next = NULL;
|
|
|
|
recptr = XLogInsert(RM_BTREE_ID, XLOG_BTREE_DELETE, rdata);
|
|
|
|
PageSetLSN(page, recptr);
|
|
PageSetSUI(page, ThisStartUpID);
|
|
}
|
|
END_CRIT_SECTION();
|
|
|
|
/* write the buffer and release the lock */
|
|
_bt_wrtbuf(rel, buf);
|
|
}
|