greenplumn nbtpage 源码
greenplumn nbtpage 代码
文件路径：/src/backend/access/nbtree/nbtpage.c
/*-------------------------------------------------------------------------
*
* nbtpage.c
* BTree-specific page management code for the Postgres btree access
* method.
*
* Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
*
* IDENTIFICATION
* src/backend/access/nbtree/nbtpage.c
*
* 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 "access/nbtree.h"
#include "access/nbtxlog.h"
#include "access/transam.h"
#include "access/xlog.h"
#include "access/xloginsert.h"
#include "miscadmin.h"
#include "storage/indexfsm.h"
#include "storage/lmgr.h"
#include "storage/predicate.h"
#include "utils/snapmgr.h"
static void _bt_cachemetadata(Relation rel, BTMetaPageData *input);
static BTMetaPageData *_bt_getmeta(Relation rel, Buffer metabuf);
static bool _bt_mark_page_halfdead(Relation rel, Buffer buf, BTStack stack);
static bool _bt_unlink_halfdead_page(Relation rel, Buffer leafbuf,
bool *rightsib_empty);
static bool _bt_lock_branch_parent(Relation rel, BlockNumber child,
BTStack stack, Buffer *topparent, OffsetNumber *topoff,
BlockNumber *target, BlockNumber *rightsib);
static void _bt_log_reuse_page(Relation rel, BlockNumber blkno,
TransactionId latestRemovedXid);
/*
* _bt_initmetapage() -- Fill a page buffer with a correct metapage image
*/
void
_bt_initmetapage(Page page, BlockNumber rootbknum, uint32 level)
{
BTMetaPageData *metad;
BTPageOpaque metaopaque;
_bt_pageinit(page, BLCKSZ);
metad = BTPageGetMeta(page);
metad->btm_magic = BTREE_MAGIC;
metad->btm_version = BTREE_VERSION;
metad->btm_root = rootbknum;
metad->btm_level = level;
metad->btm_fastroot = rootbknum;
metad->btm_fastlevel = level;
metad->btm_oldest_btpo_xact = InvalidTransactionId;
metad->btm_last_cleanup_num_heap_tuples = -1.0;
metaopaque = (BTPageOpaque) PageGetSpecialPointer(page);
metaopaque->btpo_flags = BTP_META;
/*
* Set pd_lower just past the end of the metadata. This is essential,
* because without doing so, metadata will be lost if xlog.c compresses
* the page.
*/
((PageHeader) page)->pd_lower =
((char *) metad + sizeof(BTMetaPageData)) - (char *) page;
}
/*
* _bt_upgrademetapage() -- Upgrade a meta-page from an old format to version
* 3, the last version that can be updated without broadly affecting
* on-disk compatibility. (A REINDEX is required to upgrade to v4.)
*
* This routine does purely in-memory image upgrade. Caller is
* responsible for locking, WAL-logging etc.
*/
void
_bt_upgrademetapage(Page page)
{
BTMetaPageData *metad;
BTPageOpaque metaopaque PG_USED_FOR_ASSERTS_ONLY;
metad = BTPageGetMeta(page);
metaopaque = (BTPageOpaque) PageGetSpecialPointer(page);
/* It must be really a meta page of upgradable version */
Assert(metaopaque->btpo_flags & BTP_META);
Assert(metad->btm_version < BTREE_NOVAC_VERSION);
Assert(metad->btm_version >= BTREE_MIN_VERSION);
/* Set version number and fill extra fields added into version 3 */
metad->btm_version = BTREE_NOVAC_VERSION;
metad->btm_oldest_btpo_xact = InvalidTransactionId;
metad->btm_last_cleanup_num_heap_tuples = -1.0;
/* Adjust pd_lower (see _bt_initmetapage() for details) */
((PageHeader) page)->pd_lower =
((char *) metad + sizeof(BTMetaPageData)) - (char *) page;
}
/*
* Cache metadata from input meta page to rel->rd_amcache.
*/
static void
_bt_cachemetadata(Relation rel, BTMetaPageData *input)
{
BTMetaPageData *cached_metad;
/* We assume rel->rd_amcache was already freed by caller */
Assert(rel->rd_amcache == NULL);
rel->rd_amcache = MemoryContextAlloc(rel->rd_indexcxt,
sizeof(BTMetaPageData));
/* Meta page should be of supported version */
Assert(input->btm_version >= BTREE_MIN_VERSION &&
input->btm_version <= BTREE_VERSION);
cached_metad = (BTMetaPageData *) rel->rd_amcache;
if (input->btm_version >= BTREE_NOVAC_VERSION)
{
/* Version with compatible meta-data, no need to upgrade */
memcpy(cached_metad, input, sizeof(BTMetaPageData));
}
else
{
/*
* Upgrade meta-data: copy available information from meta-page and
* fill new fields with default values.
*
* Note that we cannot upgrade to version 4+ without a REINDEX, since
* extensive on-disk changes are required.
*/
memcpy(cached_metad, input, offsetof(BTMetaPageData, btm_oldest_btpo_xact));
cached_metad->btm_version = BTREE_NOVAC_VERSION;
cached_metad->btm_oldest_btpo_xact = InvalidTransactionId;
cached_metad->btm_last_cleanup_num_heap_tuples = -1.0;
}
}
/*
* Get metadata from share-locked buffer containing metapage, while performing
* standard sanity checks. Sanity checks here must match _bt_getroot().
*/
static BTMetaPageData *
_bt_getmeta(Relation rel, Buffer metabuf)
{
Page metapg;
BTPageOpaque metaopaque;
BTMetaPageData *metad;
metapg = BufferGetPage(metabuf);
metaopaque = (BTPageOpaque) PageGetSpecialPointer(metapg);
metad = BTPageGetMeta(metapg);
/* sanity-check the metapage */
if (!P_ISMETA(metaopaque) ||
metad->btm_magic != BTREE_MAGIC)
ereport(ERROR,
(errcode(ERRCODE_INDEX_CORRUPTED),
errmsg("index \"%s\" is not a btree",
RelationGetRelationName(rel))));
if (metad->btm_version < BTREE_MIN_VERSION ||
metad->btm_version > BTREE_VERSION)
ereport(ERROR,
(errcode(ERRCODE_INDEX_CORRUPTED),
errmsg("version mismatch in index \"%s\": file version %d, "
"current version %d, minimal supported version %d",
RelationGetRelationName(rel),
metad->btm_version, BTREE_VERSION, BTREE_MIN_VERSION)));
return metad;
}
/*
* _bt_update_meta_cleanup_info() -- Update cleanup-related information in
* the metapage.
*
* This routine checks if provided cleanup-related information is matching
* to those written in the metapage. On mismatch, metapage is overwritten.
*/
void
_bt_update_meta_cleanup_info(Relation rel, TransactionId oldestBtpoXact,
float8 numHeapTuples)
{
Buffer metabuf;
Page metapg;
BTMetaPageData *metad;
bool needsRewrite = false;
XLogRecPtr recptr;
/* read the metapage and check if it needs rewrite */
metabuf = _bt_getbuf(rel, BTREE_METAPAGE, BT_READ);
metapg = BufferGetPage(metabuf);
metad = BTPageGetMeta(metapg);
/* outdated version of metapage always needs rewrite */
if (metad->btm_version < BTREE_NOVAC_VERSION)
needsRewrite = true;
else if (metad->btm_oldest_btpo_xact != oldestBtpoXact ||
metad->btm_last_cleanup_num_heap_tuples != numHeapTuples)
needsRewrite = true;
if (!needsRewrite)
{
_bt_relbuf(rel, metabuf);
return;
}
/* trade in our read lock for a write lock */
LockBuffer(metabuf, BUFFER_LOCK_UNLOCK);
LockBuffer(metabuf, BT_WRITE);
START_CRIT_SECTION();
/* upgrade meta-page if needed */
if (metad->btm_version < BTREE_NOVAC_VERSION)
_bt_upgrademetapage(metapg);
/* update cleanup-related information */
metad->btm_oldest_btpo_xact = oldestBtpoXact;
metad->btm_last_cleanup_num_heap_tuples = numHeapTuples;
MarkBufferDirty(metabuf);
/* write wal record if needed */
if (RelationNeedsWAL(rel))
{
xl_btree_metadata md;
XLogBeginInsert();
XLogRegisterBuffer(0, metabuf, REGBUF_WILL_INIT | REGBUF_STANDARD);
Assert(metad->btm_version >= BTREE_NOVAC_VERSION);
md.version = metad->btm_version;
md.root = metad->btm_root;
md.level = metad->btm_level;
md.fastroot = metad->btm_fastroot;
md.fastlevel = metad->btm_fastlevel;
md.oldest_btpo_xact = oldestBtpoXact;
md.last_cleanup_num_heap_tuples = numHeapTuples;
XLogRegisterBufData(0, (char *) &md, sizeof(xl_btree_metadata));
recptr = XLogInsert(RM_BTREE_ID, XLOG_BTREE_META_CLEANUP);
PageSetLSN(metapg, recptr);
}
END_CRIT_SECTION();
_bt_relbuf(rel, metabuf);
}
/*
* _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 intricate 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!
*
* The returned page is not necessarily the true root --- it could be
* a "fast root" (a page that is alone in its level due to deletions).
* Also, if the root page is split while we are "in flight" to it,
* what we will return is the old root, which is now just the leftmost
* page on a probably-not-very-wide level. For most purposes this is
* as good as or better than the true root, so we do not bother to
* insist on finding the true root. We do, however, guarantee to
* return a live (not deleted or half-dead) page.
*
* 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;
uint32 rootlevel;
BTMetaPageData *metad;
/*
* Try to use previously-cached metapage data to find the root. This
* normally saves one buffer access per index search, which is a very
* helpful savings in bufmgr traffic and hence contention.
*/
if (rel->rd_amcache != NULL)
{
metad = (BTMetaPageData *) rel->rd_amcache;
/* We shouldn't have cached it if any of these fail */
Assert(metad->btm_magic == BTREE_MAGIC);
Assert(metad->btm_version >= BTREE_MIN_VERSION);
Assert(metad->btm_version <= BTREE_VERSION);
Assert(metad->btm_root != P_NONE);
rootblkno = metad->btm_fastroot;
Assert(rootblkno != P_NONE);
rootlevel = metad->btm_fastlevel;
rootbuf = _bt_getbuf(rel, rootblkno, BT_READ);
rootpage = BufferGetPage(rootbuf);
rootopaque = (BTPageOpaque) PageGetSpecialPointer(rootpage);
/*
* Since the cache might be stale, we check the page more carefully
* here than normal. We *must* check that it's not deleted. If it's
* not alone on its level, then we reject too --- this may be overly
* paranoid but better safe than sorry. Note we don't check P_ISROOT,
* because that's not set in a "fast root".
*/
if (!P_IGNORE(rootopaque) &&
rootopaque->btpo.level == rootlevel &&
P_LEFTMOST(rootopaque) &&
P_RIGHTMOST(rootopaque))
{
/* OK, accept cached page as the root */
return rootbuf;
}
_bt_relbuf(rel, rootbuf);
/* Cache is stale, throw it away */
if (rel->rd_amcache)
pfree(rel->rd_amcache);
rel->rd_amcache = NULL;
}
metabuf = _bt_getbuf(rel, BTREE_METAPAGE, BT_READ);
metapg = BufferGetPage(metabuf);
metaopaque = (BTPageOpaque) PageGetSpecialPointer(metapg);
metad = BTPageGetMeta(metapg);
/* sanity-check the metapage */
if (!P_ISMETA(metaopaque) ||
metad->btm_magic != BTREE_MAGIC)
ereport(ERROR,
(errcode(ERRCODE_INDEX_CORRUPTED),
errmsg("index \"%s\" is not a btree",
RelationGetRelationName(rel))));
if (metad->btm_version < BTREE_MIN_VERSION ||
metad->btm_version > BTREE_VERSION)
ereport(ERROR,
(errcode(ERRCODE_INDEX_CORRUPTED),
errmsg("version mismatch in index \"%s\": file version %d, "
"current version %d, minimal supported version %d",
RelationGetRelationName(rel),
metad->btm_version, BTREE_VERSION, BTREE_MIN_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);
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, we
* must avoid doing it again.
*/
if (metad->btm_root != P_NONE)
{
/*
* Metadata initialized by someone else. In order to guarantee no
* deadlocks, we have to release the metadata page and start all
* over again. (Is that really true? But it's hardly worth trying
* to optimize this case.)
*/
_bt_relbuf(rel, metabuf);
return _bt_getroot(rel, access);
}
/*
* 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);
rootopaque = (BTPageOpaque) PageGetSpecialPointer(rootpage);
rootopaque->btpo_prev = rootopaque->btpo_next = P_NONE;
rootopaque->btpo_flags = (BTP_LEAF | BTP_ROOT);
rootopaque->btpo.level = 0;
rootopaque->btpo_cycleid = 0;
/* NO ELOG(ERROR) till meta is updated */
START_CRIT_SECTION();
/* upgrade metapage if needed */
if (metad->btm_version < BTREE_NOVAC_VERSION)
_bt_upgrademetapage(metapg);
metad->btm_root = rootblkno;
metad->btm_level = 0;
metad->btm_fastroot = rootblkno;
metad->btm_fastlevel = 0;
metad->btm_oldest_btpo_xact = InvalidTransactionId;
metad->btm_last_cleanup_num_heap_tuples = -1.0;
MarkBufferDirty(rootbuf);
MarkBufferDirty(metabuf);
/* XLOG stuff */
if (RelationNeedsWAL(rel))
{
xl_btree_newroot xlrec;
XLogRecPtr recptr;
xl_btree_metadata md;
XLogBeginInsert();
XLogRegisterBuffer(0, rootbuf, REGBUF_WILL_INIT);
XLogRegisterBuffer(2, metabuf, REGBUF_WILL_INIT | REGBUF_STANDARD);
Assert(metad->btm_version >= BTREE_NOVAC_VERSION);
md.version = metad->btm_version;
md.root = rootblkno;
md.level = 0;
md.fastroot = rootblkno;
md.fastlevel = 0;
md.oldest_btpo_xact = InvalidTransactionId;
md.last_cleanup_num_heap_tuples = -1.0;
XLogRegisterBufData(2, (char *) &md, sizeof(xl_btree_metadata));
xlrec.rootblk = rootblkno;
xlrec.level = 0;
XLogRegisterData((char *) &xlrec, SizeOfBtreeNewroot);
recptr = XLogInsert(RM_BTREE_ID, XLOG_BTREE_NEWROOT);
PageSetLSN(rootpage, recptr);
PageSetLSN(metapg, recptr);
}
END_CRIT_SECTION();
/*
* swap root write lock for read lock. There is no danger of anyone
* else accessing the new root page while it's unlocked, since no one
* else knows where it is yet.
*/
LockBuffer(rootbuf, BUFFER_LOCK_UNLOCK);
LockBuffer(rootbuf, BT_READ);
/* okay, metadata is correct, release lock on it */
_bt_relbuf(rel, metabuf);
}
else
{
rootblkno = metad->btm_fastroot;
Assert(rootblkno != P_NONE);
rootlevel = metad->btm_fastlevel;
/*
* Cache the metapage data for next time
*/
_bt_cachemetadata(rel, metad);
/*
* We are done with the metapage; arrange to release it via first
* _bt_relandgetbuf call
*/
rootbuf = metabuf;
for (;;)
{
rootbuf = _bt_relandgetbuf(rel, rootbuf, rootblkno, BT_READ);
rootpage = BufferGetPage(rootbuf);
rootopaque = (BTPageOpaque) PageGetSpecialPointer(rootpage);
if (!P_IGNORE(rootopaque))
break;
/* it's dead, Jim. step right one page */
if (P_RIGHTMOST(rootopaque))
elog(ERROR, "no live root page found in index \"%s\"",
RelationGetRelationName(rel));
rootblkno = rootopaque->btpo_next;
}
/* Note: can't check btpo.level on deleted pages */
if (rootopaque->btpo.level != rootlevel)
elog(ERROR, "root page %u of index \"%s\" has level %u, expected %u",
rootblkno, RelationGetRelationName(rel),
rootopaque->btpo.level, rootlevel);
}
/*
* By here, we have a pin and read lock on the root page, and no lock set
* on the metadata page. Return the root page's buffer.
*/
return rootbuf;
}
/*
* _bt_gettrueroot() -- Get the true root page of the btree.
*
* This is the same as the BT_READ case of _bt_getroot(), except
* we follow the true-root link not the fast-root link.
*
* By the time we acquire lock on the root page, it might have been split and
* not be the true root anymore. This is okay for the present uses of this
* routine; we only really need to be able to move up at least one tree level
* from whatever non-root page we were at. If we ever do need to lock the
* one true root page, we could loop here, re-reading the metapage on each
* failure. (Note that it wouldn't do to hold the lock on the metapage while
* moving to the root --- that'd deadlock against any concurrent root split.)
*/
Buffer
_bt_gettrueroot(Relation rel)
{
Buffer metabuf;
Page metapg;
BTPageOpaque metaopaque;
Buffer rootbuf;
Page rootpage;
BTPageOpaque rootopaque;
BlockNumber rootblkno;
uint32 rootlevel;
BTMetaPageData *metad;
/*
* We don't try to use cached metapage data here, since (a) this path is
* not performance-critical, and (b) if we are here it suggests our cache
* is out-of-date anyway. In light of point (b), it's probably safest to
* actively flush any cached metapage info.
*/
if (rel->rd_amcache)
pfree(rel->rd_amcache);
rel->rd_amcache = NULL;
metabuf = _bt_getbuf(rel, BTREE_METAPAGE, BT_READ);
metapg = BufferGetPage(metabuf);
metaopaque = (BTPageOpaque) PageGetSpecialPointer(metapg);
metad = BTPageGetMeta(metapg);
if (!P_ISMETA(metaopaque) ||
metad->btm_magic != BTREE_MAGIC)
ereport(ERROR,
(errcode(ERRCODE_INDEX_CORRUPTED),
errmsg("index \"%s\" is not a btree",
RelationGetRelationName(rel))));
if (metad->btm_version < BTREE_MIN_VERSION ||
metad->btm_version > BTREE_VERSION)
ereport(ERROR,
(errcode(ERRCODE_INDEX_CORRUPTED),
errmsg("version mismatch in index \"%s\": file version %d, "
"current version %d, minimal supported version %d",
RelationGetRelationName(rel),
metad->btm_version, BTREE_VERSION, BTREE_MIN_VERSION)));
/* if no root page initialized yet, fail */
if (metad->btm_root == P_NONE)
{
_bt_relbuf(rel, metabuf);
return InvalidBuffer;
}
rootblkno = metad->btm_root;
rootlevel = metad->btm_level;
/*
* We are done with the metapage; arrange to release it via first
* _bt_relandgetbuf call
*/
rootbuf = metabuf;
for (;;)
{
rootbuf = _bt_relandgetbuf(rel, rootbuf, rootblkno, BT_READ);
rootpage = BufferGetPage(rootbuf);
rootopaque = (BTPageOpaque) PageGetSpecialPointer(rootpage);
if (!P_IGNORE(rootopaque))
break;
/* it's dead, Jim. step right one page */
if (P_RIGHTMOST(rootopaque))
elog(ERROR, "no live root page found in index \"%s\"",
RelationGetRelationName(rel));
rootblkno = rootopaque->btpo_next;
}
/* Note: can't check btpo.level on deleted pages */
if (rootopaque->btpo.level != rootlevel)
elog(ERROR, "root page %u of index \"%s\" has level %u, expected %u",
rootblkno, RelationGetRelationName(rel),
rootopaque->btpo.level, rootlevel);
return rootbuf;
}
/*
* _bt_getrootheight() -- Get the height of the btree search tree.
*
* We return the level (counting from zero) of the current fast root.
* This represents the number of tree levels we'd have to descend through
* to start any btree index search.
*
* This is used by the planner for cost-estimation purposes. Since it's
* only an estimate, slightly-stale data is fine, hence we don't worry
* about updating previously cached data.
*/
int
_bt_getrootheight(Relation rel)
{
BTMetaPageData *metad;
if (rel->rd_amcache == NULL)
{
Buffer metabuf;
metabuf = _bt_getbuf(rel, BTREE_METAPAGE, BT_READ);
metad = _bt_getmeta(rel, metabuf);
/*
* If there's no root page yet, _bt_getroot() doesn't expect a cache
* to be made, so just stop here and report the index height is zero.
* (XXX perhaps _bt_getroot() should be changed to allow this case.)
*/
if (metad->btm_root == P_NONE)
{
_bt_relbuf(rel, metabuf);
return 0;
}
/*
* Cache the metapage data for next time
*/
_bt_cachemetadata(rel, metad);
/* We shouldn't have cached it if any of these fail */
Assert(metad->btm_magic == BTREE_MAGIC);
Assert(metad->btm_version >= BTREE_NOVAC_VERSION);
Assert(metad->btm_fastroot != P_NONE);
_bt_relbuf(rel, metabuf);
}
/* Get cached page */
metad = (BTMetaPageData *) rel->rd_amcache;
return metad->btm_fastlevel;
}
/*
* _bt_heapkeyspace() -- is heap TID being treated as a key?
*
* This is used to determine the rules that must be used to descend a
* btree. Version 4 indexes treat heap TID as a tiebreaker attribute.
* pg_upgrade'd version 3 indexes need extra steps to preserve reasonable
* performance when inserting a new BTScanInsert-wise duplicate tuple
* among many leaf pages already full of such duplicates.
*/
bool
_bt_heapkeyspace(Relation rel)
{
BTMetaPageData *metad;
if (rel->rd_amcache == NULL)
{
Buffer metabuf;
metabuf = _bt_getbuf(rel, BTREE_METAPAGE, BT_READ);
metad = _bt_getmeta(rel, metabuf);
/*
* If there's no root page yet, _bt_getroot() doesn't expect a cache
* to be made, so just stop here. (XXX perhaps _bt_getroot() should
* be changed to allow this case.)
*/
if (metad->btm_root == P_NONE)
{
uint32 btm_version = metad->btm_version;
_bt_relbuf(rel, metabuf);
return btm_version > BTREE_NOVAC_VERSION;
}
/*
* Cache the metapage data for next time
*/
_bt_cachemetadata(rel, metad);
/* We shouldn't have cached it if any of these fail */
Assert(metad->btm_magic == BTREE_MAGIC);
Assert(metad->btm_version >= BTREE_NOVAC_VERSION);
Assert(metad->btm_fastroot != P_NONE);
_bt_relbuf(rel, metabuf);
}
/* Get cached page */
metad = (BTMetaPageData *) rel->rd_amcache;
return metad->btm_version > BTREE_NOVAC_VERSION;
}
/*
* _bt_checkpage() -- Verify that a freshly-read page looks sane.
*/
void
_bt_checkpage(Relation rel, Buffer buf)
{
Page page = BufferGetPage(buf);
/*
* ReadBuffer verifies that every newly-read page passes
* PageHeaderIsValid, which means it either contains a reasonably sane
* page header or is all-zero. We have to defend against the all-zero
* case, however.
*/
if (PageIsNew(page))
ereport(ERROR,
(errcode(ERRCODE_INDEX_CORRUPTED),
errmsg("index \"%s\" contains unexpected zero page at block %u",
RelationGetRelationName(rel),
BufferGetBlockNumber(buf)),
errhint("Please REINDEX it.")));
/*
* Additionally check that the special area looks sane.
*/
if (PageGetSpecialSize(page) != MAXALIGN(sizeof(BTPageOpaqueData)))
ereport(ERROR,
(errcode(ERRCODE_INDEX_CORRUPTED),
errmsg("index \"%s\" contains corrupted page at block %u",
RelationGetRelationName(rel),
BufferGetBlockNumber(buf)),
errhint("Please REINDEX it.")));
}
/*
* Log the reuse of a page from the FSM.
*/
static void
_bt_log_reuse_page(Relation rel, BlockNumber blkno, TransactionId latestRemovedXid)
{
xl_btree_reuse_page xlrec_reuse;
/*
* Note that we don't register the buffer with the record, because this
* operation doesn't modify the page. This record only exists to provide a
* conflict point for Hot Standby.
*/
/* XLOG stuff */
xlrec_reuse.node = rel->rd_node;
xlrec_reuse.block = blkno;
xlrec_reuse.latestRemovedXid = latestRemovedXid;
XLogBeginInsert();
XLogRegisterData((char *) &xlrec_reuse, SizeOfBtreeReusePage);
XLogInsert(RM_BTREE_ID, XLOG_BTREE_REUSE_PAGE);
}
/*
* _bt_getbuf() -- Get a buffer by block number for read or write.
*
* blkno == P_NEW means to get an unallocated index page. The page
* will be initialized before returning it.
*
* 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"). Also, we apply
* _bt_checkpage to sanity-check the page (except in P_NEW case).
*/
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);
_bt_checkpage(rel, buf);
}
else
{
bool needLock;
Page page;
Assert(access == BT_WRITE);
/*
* First see if the FSM knows of any free pages.
*
* We can't trust the FSM's report unreservedly; we have to check that
* the page is still free. (For example, an already-free page could
* have been re-used between the time the last VACUUM scanned it and
* the time the VACUUM made its FSM updates.)
*
* In fact, it's worse than that: we can't even assume that it's safe
* to take a lock on the reported page. If somebody else has a lock
* on it, or even worse our own caller does, we could deadlock. (The
* own-caller scenario is actually not improbable. Consider an index
* on a serial or timestamp column. Nearly all splits will be at the
* rightmost page, so it's entirely likely that _bt_split will call us
* while holding a lock on the page most recently acquired from FSM. A
* VACUUM running concurrently with the previous split could well have
* placed that page back in FSM.)
*
* To get around that, we ask for only a conditional lock on the
* reported page. If we fail, then someone else is using the page,
* and we may reasonably assume it's not free. (If we happen to be
* wrong, the worst consequence is the page will be lost to use till
* the next VACUUM, which is no big problem.)
*/
for (;;)
{
blkno = GetFreeIndexPage(rel);
if (blkno == InvalidBlockNumber)
break;
buf = ReadBuffer(rel, blkno);
if (ConditionalLockBuffer(buf))
{
page = BufferGetPage(buf);
if (_bt_page_recyclable(page))
{
/*
* If we are generating WAL for Hot Standby then create a
* WAL record that will allow us to conflict with queries
* running on standby, in case they have snapshots older
* than btpo.xact. This can only apply if the page does
* have a valid btpo.xact value, ie not if it's new. (We
* must check that because an all-zero page has no special
* space.)
*/
if (XLogStandbyInfoActive() && RelationNeedsWAL(rel) &&
!PageIsNew(page))
{
BTPageOpaque opaque = (BTPageOpaque) PageGetSpecialPointer(page);
_bt_log_reuse_page(rel, blkno, opaque->btpo.xact);
}
/* Okay to use page. Re-initialize and return it */
_bt_pageinit(page, BufferGetPageSize(buf));
return buf;
}
elog(DEBUG2, "FSM returned nonrecyclable page");
_bt_relbuf(rel, buf);
}
else
{
elog(DEBUG2, "FSM returned nonlockable page");
/* couldn't get lock, so just drop pin */
ReleaseBuffer(buf);
}
}
/*
* Extend the relation by one page.
*
* 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(rel);
if (needLock)
LockRelationForExtension(rel, ExclusiveLock);
buf = ReadBuffer(rel, P_NEW);
/* Acquire buffer lock on new page */
LockBuffer(buf, BT_WRITE);
/*
* 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 btvacuumscan --- see comments therein.
*/
if (needLock)
UnlockRelationForExtension(rel, ExclusiveLock);
/* Initialize the new page before returning it */
page = BufferGetPage(buf);
Assert(PageIsNew(page));
_bt_pageinit(page, BufferGetPageSize(buf));
}
/* ref count and lock type are correct */
return buf;
}
/*
* _bt_relandgetbuf() -- release a locked buffer and get another one.
*
* This is equivalent to _bt_relbuf followed by _bt_getbuf, with the
* exception that blkno may not be P_NEW. Also, if obuf is InvalidBuffer
* then it reduces to just _bt_getbuf; allowing this case simplifies some
* callers.
*
* The original motivation for using this was to avoid two entries to the
* bufmgr when one would do. However, now it's mainly just a notational
* convenience. The only case where it saves work over _bt_relbuf/_bt_getbuf
* is when the target page is the same one already in the buffer.
*/
Buffer
_bt_relandgetbuf(Relation rel, Buffer obuf, BlockNumber blkno, int access)
{
Buffer buf;
Assert(blkno != P_NEW);
if (BufferIsValid(obuf))
LockBuffer(obuf, BUFFER_LOCK_UNLOCK);
buf = ReleaseAndReadBuffer(obuf, rel, blkno);
LockBuffer(buf, access);
_bt_checkpage(rel, buf);
return buf;
}
/*
* _bt_relbuf() -- release a locked buffer.
*
* Lock and pin (refcount) are both dropped.
*/
void
_bt_relbuf(Relation rel, Buffer buf)
{
UnlockReleaseBuffer(buf);
}
/*
* _bt_pageinit() -- Initialize a new page.
*
* On return, the page header is initialized; data space is empty;
* special space is zeroed out.
*/
void
_bt_pageinit(Page page, Size size)
{
PageInit(page, size, sizeof(BTPageOpaqueData));
}
/*
* _bt_page_recyclable() -- Is an existing page recyclable?
*
* This exists to make sure _bt_getbuf and btvacuumscan have the same
* policy about whether a page is safe to re-use. But note that _bt_getbuf
* knows enough to distinguish the PageIsNew condition from the other one.
* At some point it might be appropriate to redesign this to have a three-way
* result value.
*/
bool
_bt_page_recyclable(Page page)
{
BTPageOpaque opaque;
/*
* It's possible to find an all-zeroes page in an index --- for example, a
* backend might successfully extend the relation one page and then crash
* before it is able to make a WAL entry for adding the page. If we find a
* zeroed page then reclaim it.
*/
if (PageIsNew(page))
return true;
/*
* Otherwise, recycle if deleted and too old to have any processes
* interested in it.
*/
opaque = (BTPageOpaque) PageGetSpecialPointer(page);
if (P_ISDELETED(opaque) &&
TransactionIdPrecedes(opaque->btpo.xact, RecentGlobalXmin))
return true;
return false;
}
/*
* Delete item(s) from a btree page during VACUUM.
*
* This must only be used for deleting leaf items. Deleting an item on a
* non-leaf page has to be done as part of an atomic action that includes
* deleting the page it points to.
*
* This routine assumes that the caller has pinned and locked the buffer.
* Also, the given itemnos *must* appear in increasing order in the array.
*
* We record VACUUMs and b-tree deletes differently in WAL. InHotStandby
* we need to be able to pin all of the blocks in the btree in physical
* order when replaying the effects of a VACUUM, just as we do for the
* original VACUUM itself. lastBlockVacuumed allows us to tell whether an
* intermediate range of blocks has had no changes at all by VACUUM,
* and so must be scanned anyway during replay. We always write a WAL record
* for the last block in the index, whether or not it contained any items
* to be removed. This allows us to scan right up to end of index to
* ensure correct locking.
*/
void
_bt_delitems_vacuum(Relation rel, Buffer buf,
OffsetNumber *itemnos, int nitems,
BlockNumber lastBlockVacuumed)
{
Page page = BufferGetPage(buf);
BTPageOpaque opaque;
/* No ereport(ERROR) until changes are logged */
START_CRIT_SECTION();
/* Fix the page */
if (nitems > 0)
PageIndexMultiDelete(page, itemnos, nitems);
/*
* We can clear the vacuum cycle ID since this page has certainly been
* processed by the current vacuum scan.
*/
opaque = (BTPageOpaque) PageGetSpecialPointer(page);
opaque->btpo_cycleid = 0;
/*
* Mark the page as not containing any LP_DEAD items. This is not
* certainly true (there might be some that have recently been marked, but
* weren't included in our target-item list), but it will almost always be
* true and it doesn't seem worth an additional page scan to check it.
* Remember that BTP_HAS_GARBAGE is only a hint anyway.
*/
opaque->btpo_flags &= ~BTP_HAS_GARBAGE;
MarkBufferDirty(buf);
/* XLOG stuff */
if (RelationNeedsWAL(rel))
{
XLogRecPtr recptr;
xl_btree_vacuum xlrec_vacuum;
xlrec_vacuum.lastBlockVacuumed = lastBlockVacuumed;
XLogBeginInsert();
XLogRegisterBuffer(0, buf, REGBUF_STANDARD);
XLogRegisterData((char *) &xlrec_vacuum, SizeOfBtreeVacuum);
/*
* The target-offsets array is not in the buffer, but pretend that it
* is. When XLogInsert stores the whole buffer, the offsets array
* need not be stored too.
*/
if (nitems > 0)
XLogRegisterBufData(0, (char *) itemnos, nitems * sizeof(OffsetNumber));
recptr = XLogInsert(RM_BTREE_ID, XLOG_BTREE_VACUUM);
PageSetLSN(page, recptr);
}
END_CRIT_SECTION();
}
/*
* Delete item(s) from a btree page during single-page cleanup.
*
* As above, must only be used on leaf pages.
*
* This routine assumes that the caller has pinned and locked the buffer.
* Also, the given itemnos *must* appear in increasing order in the array.
*
* This is nearly the same as _bt_delitems_vacuum as far as what it does to
* the page, but the WAL logging considerations are quite different. See
* comments for _bt_delitems_vacuum.
*/
void
_bt_delitems_delete(Relation rel, Buffer buf,
OffsetNumber *itemnos, int nitems,
Relation heapRel)
{
Page page = BufferGetPage(buf);
BTPageOpaque opaque;
TransactionId latestRemovedXid = InvalidTransactionId;
/* Shouldn't be called unless there's something to do */
Assert(nitems > 0);
if (XLogStandbyInfoActive() && RelationNeedsWAL(rel))
latestRemovedXid =
index_compute_xid_horizon_for_tuples(rel, heapRel, buf,
itemnos, nitems);
/* No ereport(ERROR) until changes are logged */
START_CRIT_SECTION();
/* Fix the page */
PageIndexMultiDelete(page, itemnos, nitems);
/*
* Unlike _bt_delitems_vacuum, we *must not* clear the vacuum cycle ID,
* because this is not called by VACUUM.
*/
/*
* Mark the page as not containing any LP_DEAD items. This is not
* certainly true (there might be some that have recently been marked, but
* weren't included in our target-item list), but it will almost always be
* true and it doesn't seem worth an additional page scan to check it.
* Remember that BTP_HAS_GARBAGE is only a hint anyway.
*/
opaque = (BTPageOpaque) PageGetSpecialPointer(page);
opaque->btpo_flags &= ~BTP_HAS_GARBAGE;
MarkBufferDirty(buf);
/* XLOG stuff */
if (RelationNeedsWAL(rel))
{
XLogRecPtr recptr;
xl_btree_delete xlrec_delete;
xlrec_delete.latestRemovedXid = latestRemovedXid;
xlrec_delete.nitems = nitems;
XLogBeginInsert();
XLogRegisterBuffer(0, buf, REGBUF_STANDARD);
XLogRegisterData((char *) &xlrec_delete, SizeOfBtreeDelete);
/*
* We need the target-offsets array whether or not we store the whole
* buffer, to allow us to find the latestRemovedXid on a standby
* server.
*/
XLogRegisterData((char *) itemnos, nitems * sizeof(OffsetNumber));
recptr = XLogInsert(RM_BTREE_ID, XLOG_BTREE_DELETE);
PageSetLSN(page, recptr);
}
END_CRIT_SECTION();
}
/*
* Returns true, if the given block has the half-dead flag set.
*/
static bool
_bt_is_page_halfdead(Relation rel, BlockNumber blk)
{
Buffer buf;
Page page;
BTPageOpaque opaque;
bool result;
buf = _bt_getbuf(rel, blk, BT_READ);
page = BufferGetPage(buf);
opaque = (BTPageOpaque) PageGetSpecialPointer(page);
result = P_ISHALFDEAD(opaque);
_bt_relbuf(rel, buf);
return result;
}
/*
* Subroutine to find the parent of the branch we're deleting. This climbs
* up the tree until it finds a page with more than one child, i.e. a page
* that will not be totally emptied by the deletion. The chain of pages below
* it, with one downlink each, will form the branch that we need to delete.
*
* If we cannot remove the downlink from the parent, because it's the
* rightmost entry, returns false. On success, *topparent and *topoff are set
* to the buffer holding the parent, and the offset of the downlink in it.
* *topparent is write-locked, the caller is responsible for releasing it when
* done. *target is set to the topmost page in the branch to-be-deleted, i.e.
* the page whose downlink *topparent / *topoff point to, and *rightsib to its
* right sibling.
*
* "child" is the leaf page we wish to delete, and "stack" is a search stack
* leading to it (it actually leads to the leftmost leaf page with a high key
* matching that of the page to be deleted in !heapkeyspace indexes). Note
* that we will update the stack entry(s) to reflect current downlink
* positions --- this is essentially the same as the corresponding step of
* splitting, and is not expected to affect caller. The caller should
* initialize *target and *rightsib to the leaf page and its right sibling.
*
* Note: it's OK to release page locks on any internal pages between the leaf
* and *topparent, because a safe deletion can't become unsafe due to
* concurrent activity. An internal page can only acquire an entry if the
* child is split, but that cannot happen as long as we hold a lock on the
* leaf.
*/
static bool
_bt_lock_branch_parent(Relation rel, BlockNumber child, BTStack stack,
Buffer *topparent, OffsetNumber *topoff,
BlockNumber *target, BlockNumber *rightsib)
{
BlockNumber parent;
OffsetNumber poffset,
maxoff;
Buffer pbuf;
Page page;
BTPageOpaque opaque;
BlockNumber leftsib;
/*
* Locate the downlink of "child" in the parent, updating the stack entry
* if needed. This is how !heapkeyspace indexes deal with having
* non-unique high keys in leaf level pages. Even heapkeyspace indexes
* can have a stale stack due to insertions into the parent.
*/
stack->bts_btentry = child;
pbuf = _bt_getstackbuf(rel, stack);
if (pbuf == InvalidBuffer)
elog(ERROR, "failed to re-find parent key in index \"%s\" for deletion target page %u",
RelationGetRelationName(rel), child);
parent = stack->bts_blkno;
poffset = stack->bts_offset;
page = BufferGetPage(pbuf);
opaque = (BTPageOpaque) PageGetSpecialPointer(page);
maxoff = PageGetMaxOffsetNumber(page);
/*
* If the target is the rightmost child of its parent, then we can't
* delete, unless it's also the only child.
*/
if (poffset >= maxoff)
{
/* It's rightmost child... */
if (poffset == P_FIRSTDATAKEY(opaque))
{
/*
* It's only child, so safe if parent would itself be removable.
* We have to check the parent itself, and then recurse to test
* the conditions at the parent's parent.
*/
if (P_RIGHTMOST(opaque) || P_ISROOT(opaque) ||
P_INCOMPLETE_SPLIT(opaque))
{
_bt_relbuf(rel, pbuf);
return false;
}
*target = parent;
*rightsib = opaque->btpo_next;
leftsib = opaque->btpo_prev;
_bt_relbuf(rel, pbuf);
/*
* Like in _bt_pagedel, check that the left sibling is not marked
* with INCOMPLETE_SPLIT flag. That would mean that there is no
* downlink to the page to be deleted, and the page deletion
* algorithm isn't prepared to handle that.
*/
if (leftsib != P_NONE)
{
Buffer lbuf;
Page lpage;
BTPageOpaque lopaque;
lbuf = _bt_getbuf(rel, leftsib, BT_READ);
lpage = BufferGetPage(lbuf);
lopaque = (BTPageOpaque) PageGetSpecialPointer(lpage);
/*
* If the left sibling was concurrently split, so that its
* next-pointer doesn't point to the current page anymore, the
* split that created the current page must be completed. (We
* don't allow splitting an incompletely split page again
* until the previous split has been completed)
*/
if (lopaque->btpo_next == parent &&
P_INCOMPLETE_SPLIT(lopaque))
{
_bt_relbuf(rel, lbuf);
return false;
}
_bt_relbuf(rel, lbuf);
}
return _bt_lock_branch_parent(rel, parent, stack->bts_parent,
topparent, topoff, target, rightsib);
}
else
{
/* Unsafe to delete */
_bt_relbuf(rel, pbuf);
return false;
}
}
else
{
/* Not rightmost child, so safe to delete */
*topparent = pbuf;
*topoff = poffset;
return true;
}
}
/*
* _bt_pagedel() -- Delete a page from the b-tree, if legal to do so.
*
* This action unlinks the page from the b-tree structure, removing all
* pointers leading to it --- but not touching its own left and right links.
* The page cannot be physically reclaimed right away, since other processes
* may currently be trying to follow links leading to the page; they have to
* be allowed to use its right-link to recover. See nbtree/README.
*
* On entry, the target buffer must be pinned and locked (either read or write
* lock is OK). This lock and pin will be dropped before exiting.
*
* Returns the number of pages successfully deleted (zero if page cannot
* be deleted now; could be more than one if parent or sibling pages were
* deleted too).
*
* NOTE: this leaks memory. Rather than trying to clean up everything
* carefully, it's better to run it in a temp context that can be reset
* frequently.
*/
int
_bt_pagedel(Relation rel, Buffer buf)
{
int ndeleted = 0;
BlockNumber rightsib;
bool rightsib_empty;
Page page;
BTPageOpaque opaque;
/*
* "stack" is a search stack leading (approximately) to the target page.
* It is initially NULL, but when iterating, we keep it to avoid
* duplicated search effort.
*
* Also, when "stack" is not NULL, we have already checked that the
* current page is not the right half of an incomplete split, i.e. the
* left sibling does not have its INCOMPLETE_SPLIT flag set.
*/
BTStack stack = NULL;
for (;;)
{
page = BufferGetPage(buf);
opaque = (BTPageOpaque) PageGetSpecialPointer(page);
/*
* Internal pages are never deleted directly, only as part of deleting
* the whole branch all the way down to leaf level.
*/
if (!P_ISLEAF(opaque))
{
/*
* Pre-9.4 page deletion only marked internal pages as half-dead,
* but now we only use that flag on leaf pages. The old algorithm
* was never supposed to leave half-dead pages in the tree, it was
* just a transient state, but it was nevertheless possible in
* error scenarios. We don't know how to deal with them here. They
* are harmless as far as searches are considered, but inserts
* into the deleted keyspace could add out-of-order downlinks in
* the upper levels. Log a notice, hopefully the admin will notice
* and reindex.
*/
if (P_ISHALFDEAD(opaque))
ereport(LOG,
(errcode(ERRCODE_INDEX_CORRUPTED),
errmsg("index \"%s\" contains a half-dead internal page",
RelationGetRelationName(rel)),
errhint("This can be caused by an interrupted VACUUM in version 9.3 or older, before upgrade. Please REINDEX it.")));
_bt_relbuf(rel, buf);
return ndeleted;
}
/*
* We can never delete rightmost pages nor root pages. While at it,
* check that page is not already deleted and is empty.
*
* To keep the algorithm simple, we also never delete an incompletely
* split page (they should be rare enough that this doesn't make any
* meaningful difference to disk usage):
*
* The INCOMPLETE_SPLIT flag on the page tells us if the page is the
* left half of an incomplete split, but ensuring that it's not the
* right half is more complicated. For that, we have to check that
* the left sibling doesn't have its INCOMPLETE_SPLIT flag set. On
* the first iteration, we temporarily release the lock on the current
* page, and check the left sibling and also construct a search stack
* to. On subsequent iterations, we know we stepped right from a page
* that passed these tests, so it's OK.
*/
if (P_RIGHTMOST(opaque) || P_ISROOT(opaque) || P_ISDELETED(opaque) ||
P_FIRSTDATAKEY(opaque) <= PageGetMaxOffsetNumber(page) ||
P_INCOMPLETE_SPLIT(opaque))
{
/* Should never fail to delete a half-dead page */
Assert(!P_ISHALFDEAD(opaque));
_bt_relbuf(rel, buf);
return ndeleted;
}
/*
* First, remove downlink pointing to the page (or a parent of the
* page, if we are going to delete a taller branch), and mark the page
* as half-dead.
*/
if (!P_ISHALFDEAD(opaque))
{
/*
* We need an approximate pointer to the page's parent page. We
* use a variant of the standard search mechanism to search for
* the page's high key; this will give us a link to either the
* current parent or someplace to its left (if there are multiple
* equal high keys, which is possible with !heapkeyspace indexes).
*
* Also check if this is the right-half of an incomplete split
* (see comment above).
*/
if (!stack)
{
BTScanInsert itup_key;
ItemId itemid;
IndexTuple targetkey;
Buffer lbuf;
BlockNumber leftsib;
itemid = PageGetItemId(page, P_HIKEY);
targetkey = CopyIndexTuple((IndexTuple) PageGetItem(page, itemid));
leftsib = opaque->btpo_prev;
/*
* To avoid deadlocks, we'd better drop the leaf page lock
* before going further.
*/
LockBuffer(buf, BUFFER_LOCK_UNLOCK);
/*
* Fetch the left sibling, to check that it's not marked with
* INCOMPLETE_SPLIT flag. That would mean that the page
* to-be-deleted doesn't have a downlink, and the page
* deletion algorithm isn't prepared to handle that.
*/
if (!P_LEFTMOST(opaque))
{
BTPageOpaque lopaque;
Page lpage;
lbuf = _bt_getbuf(rel, leftsib, BT_READ);
lpage = BufferGetPage(lbuf);
lopaque = (BTPageOpaque) PageGetSpecialPointer(lpage);
/*
* If the left sibling is split again by another backend,
* after we released the lock, we know that the first
* split must have finished, because we don't allow an
* incompletely-split page to be split again. So we don't
* need to walk right here.
*/
if (lopaque->btpo_next == BufferGetBlockNumber(buf) &&
P_INCOMPLETE_SPLIT(lopaque))
{
ReleaseBuffer(buf);
_bt_relbuf(rel, lbuf);
return ndeleted;
}
_bt_relbuf(rel, lbuf);
}
/* we need an insertion scan key for the search, so build one */
itup_key = _bt_mkscankey(rel, targetkey);
/* find the leftmost leaf page with matching pivot/high key */
itup_key->pivotsearch = true;
stack = _bt_search(rel, itup_key, &lbuf, BT_READ, NULL);
/* don't need a lock or second pin on the page */
_bt_relbuf(rel, lbuf);
/*
* Re-lock the leaf page, and start over, to re-check that the
* page can still be deleted.
*/
LockBuffer(buf, BT_WRITE);
continue;
}
if (!_bt_mark_page_halfdead(rel, buf, stack))
{
_bt_relbuf(rel, buf);
return ndeleted;
}
}
/*
* Then unlink it from its siblings. Each call to
* _bt_unlink_halfdead_page unlinks the topmost page from the branch,
* making it shallower. Iterate until the leaf page is gone.
*/
rightsib_empty = false;
while (P_ISHALFDEAD(opaque))
{
/* will check for interrupts, once lock is released */
if (!_bt_unlink_halfdead_page(rel, buf, &rightsib_empty))
{
/* _bt_unlink_halfdead_page already released buffer */
return ndeleted;
}
ndeleted++;
}
rightsib = opaque->btpo_next;
_bt_relbuf(rel, buf);
/*
* Check here, as calling loops will have locks held, preventing
* interrupts from being processed.
*/
CHECK_FOR_INTERRUPTS();
/*
* The page has now been deleted. If its right sibling is completely
* empty, it's possible that the reason we haven't deleted it earlier
* is that it was the rightmost child of the parent. Now that we
* removed the downlink for this page, the right sibling might now be
* the only child of the parent, and could be removed. It would be
* picked up by the next vacuum anyway, but might as well try to
* remove it now, so loop back to process the right sibling.
*/
if (!rightsib_empty)
break;
buf = _bt_getbuf(rel, rightsib, BT_WRITE);
}
return ndeleted;
}
/*
* First stage of page deletion. Remove the downlink to the top of the
* branch being deleted, and mark the leaf page as half-dead.
*/
static bool
_bt_mark_page_halfdead(Relation rel, Buffer leafbuf, BTStack stack)
{
BlockNumber leafblkno;
BlockNumber leafrightsib;
BlockNumber target;
BlockNumber rightsib;
ItemId itemid;
Page page;
BTPageOpaque opaque;
Buffer topparent;
OffsetNumber topoff;
OffsetNumber nextoffset;
IndexTuple itup;
IndexTupleData trunctuple;
page = BufferGetPage(leafbuf);
opaque = (BTPageOpaque) PageGetSpecialPointer(page);
Assert(!P_RIGHTMOST(opaque) && !P_ISROOT(opaque) && !P_ISDELETED(opaque) &&
!P_ISHALFDEAD(opaque) && P_ISLEAF(opaque) &&
P_FIRSTDATAKEY(opaque) > PageGetMaxOffsetNumber(page));
/*
* Save info about the leaf page.
*/
leafblkno = BufferGetBlockNumber(leafbuf);
leafrightsib = opaque->btpo_next;
/*
* Before attempting to lock the parent page, check that the right sibling
* is not in half-dead state. A half-dead right sibling would have no
* downlink in the parent, which would be highly confusing later when we
* delete the downlink that follows the current page's downlink. (I
* believe the deletion would work correctly, but it would fail the
* cross-check we make that the following downlink points to the right
* sibling of the delete page.)
*/
if (_bt_is_page_halfdead(rel, leafrightsib))
{
elog(DEBUG1, "could not delete page %u because its right sibling %u is half-dead",
leafblkno, leafrightsib);
return false;
}
/*
* We cannot delete a page that is the rightmost child of its immediate
* parent, unless it is the only child --- in which case the parent has to
* be deleted too, and the same condition applies recursively to it. We
* have to check this condition all the way up before trying to delete,
* and lock the final parent of the to-be-deleted subtree.
*
* However, we won't need to repeat the above _bt_is_page_halfdead() check
* for parent/ancestor pages because of the rightmost restriction. The
* leaf check will apply to a right "cousin" leaf page rather than a
* simple right sibling leaf page in cases where we actually go on to
* perform internal page deletion. The right cousin leaf page is
* representative of the left edge of the subtree to the right of the
* to-be-deleted subtree as a whole. (Besides, internal pages are never
* marked half-dead, so it isn't even possible to directly assess if an
* internal page is part of some other to-be-deleted subtree.)
*/
rightsib = leafrightsib;
target = leafblkno;
if (!_bt_lock_branch_parent(rel, leafblkno, stack,
&topparent, &topoff, &target, &rightsib))
return false;
/*
* Check that the parent-page index items we're about to delete/overwrite
* contain what we expect. This can fail if the index has become corrupt
* for some reason. We want to throw any error before entering the
* critical section --- otherwise it'd be a PANIC.
*
* The test on the target item is just an Assert because
* _bt_lock_branch_parent should have guaranteed it has the expected
* contents. The test on the next-child downlink is known to sometimes
* fail in the field, though.
*/
page = BufferGetPage(topparent);
opaque = (BTPageOpaque) PageGetSpecialPointer(page);
#ifdef USE_ASSERT_CHECKING
itemid = PageGetItemId(page, topoff);
itup = (IndexTuple) PageGetItem(page, itemid);
Assert(BTreeInnerTupleGetDownLink(itup) == target);
#endif
nextoffset = OffsetNumberNext(topoff);
itemid = PageGetItemId(page, nextoffset);
itup = (IndexTuple) PageGetItem(page, itemid);
if (BTreeInnerTupleGetDownLink(itup) != rightsib)
elog(ERROR, "right sibling %u of block %u is not next child %u of block %u in index \"%s\"",
rightsib, target, BTreeInnerTupleGetDownLink(itup),
BufferGetBlockNumber(topparent), RelationGetRelationName(rel));
/*
* Any insert which would have gone on the leaf block will now go to its
* right sibling.
*/
PredicateLockPageCombine(rel, leafblkno, leafrightsib);
/* No ereport(ERROR) until changes are logged */
START_CRIT_SECTION();
/*
* Update parent. The normal case is a tad tricky because we want to
* delete the target's downlink and the *following* key. Easiest way is
* to copy the right sibling's downlink over the target downlink, and then
* delete the following item.
*/
page = BufferGetPage(topparent);
opaque = (BTPageOpaque) PageGetSpecialPointer(page);
itemid = PageGetItemId(page, topoff);
itup = (IndexTuple) PageGetItem(page, itemid);
BTreeInnerTupleSetDownLink(itup, rightsib);
nextoffset = OffsetNumberNext(topoff);
PageIndexTupleDelete(page, nextoffset);
/*
* Mark the leaf page as half-dead, and stamp it with a pointer to the
* highest internal page in the branch we're deleting. We use the tid of
* the high key to store it.
*/
page = BufferGetPage(leafbuf);
opaque = (BTPageOpaque) PageGetSpecialPointer(page);
opaque->btpo_flags |= BTP_HALF_DEAD;
PageIndexTupleDelete(page, P_HIKEY);
Assert(PageGetMaxOffsetNumber(page) == 0);
MemSet(&trunctuple, 0, sizeof(IndexTupleData));
trunctuple.t_info = sizeof(IndexTupleData);
if (target != leafblkno)
BTreeTupleSetTopParent(&trunctuple, target);
else
BTreeTupleSetTopParent(&trunctuple, InvalidBlockNumber);
if (PageAddItem(page, (Item) &trunctuple, sizeof(IndexTupleData), P_HIKEY,
false, false) == InvalidOffsetNumber)
elog(ERROR, "could not add dummy high key to half-dead page");
/* Must mark buffers dirty before XLogInsert */
MarkBufferDirty(topparent);
MarkBufferDirty(leafbuf);
/* XLOG stuff */
if (RelationNeedsWAL(rel))
{
xl_btree_mark_page_halfdead xlrec;
XLogRecPtr recptr;
xlrec.poffset = topoff;
xlrec.leafblk = leafblkno;
if (target != leafblkno)
xlrec.topparent = target;
else
xlrec.topparent = InvalidBlockNumber;
XLogBeginInsert();
XLogRegisterBuffer(0, leafbuf, REGBUF_WILL_INIT);
XLogRegisterBuffer(1, topparent, REGBUF_STANDARD);
page = BufferGetPage(leafbuf);
opaque = (BTPageOpaque) PageGetSpecialPointer(page);
xlrec.leftblk = opaque->btpo_prev;
xlrec.rightblk = opaque->btpo_next;
XLogRegisterData((char *) &xlrec, SizeOfBtreeMarkPageHalfDead);
recptr = XLogInsert(RM_BTREE_ID, XLOG_BTREE_MARK_PAGE_HALFDEAD);
page = BufferGetPage(topparent);
PageSetLSN(page, recptr);
page = BufferGetPage(leafbuf);
PageSetLSN(page, recptr);
}
END_CRIT_SECTION();
_bt_relbuf(rel, topparent);
return true;
}
/*
* Unlink a page in a branch of half-dead pages from its siblings.
*
* If the leaf page still has a downlink pointing to it, unlinks the highest
* parent in the to-be-deleted branch instead of the leaf page. To get rid
* of the whole branch, including the leaf page itself, iterate until the
* leaf page is deleted.
*
* Returns 'false' if the page could not be unlinked (shouldn't happen).
* If the (new) right sibling of the page is empty, *rightsib_empty is set
* to true.
*
* Must hold pin and lock on leafbuf at entry (read or write doesn't matter).
* On success exit, we'll be holding pin and write lock. On failure exit,
* we'll release both pin and lock before returning (we define it that way
* to avoid having to reacquire a lock we already released).
*/
static bool
_bt_unlink_halfdead_page(Relation rel, Buffer leafbuf, bool *rightsib_empty)
{
BlockNumber leafblkno = BufferGetBlockNumber(leafbuf);
BlockNumber leafleftsib;
BlockNumber leafrightsib;
BlockNumber target;
BlockNumber leftsib;
BlockNumber rightsib;
Buffer lbuf = InvalidBuffer;
Buffer buf;
Buffer rbuf;
Buffer metabuf = InvalidBuffer;
Page metapg = NULL;
BTMetaPageData *metad = NULL;
ItemId itemid;
Page page;
BTPageOpaque opaque;
bool rightsib_is_rightmost;
int targetlevel;
IndexTuple leafhikey;
BlockNumber nextchild;
page = BufferGetPage(leafbuf);
opaque = (BTPageOpaque) PageGetSpecialPointer(page);
Assert(P_ISLEAF(opaque) && P_ISHALFDEAD(opaque));
/*
* Remember some information about the leaf page.
*/
itemid = PageGetItemId(page, P_HIKEY);
leafhikey = (IndexTuple) PageGetItem(page, itemid);
leafleftsib = opaque->btpo_prev;
leafrightsib = opaque->btpo_next;
LockBuffer(leafbuf, BUFFER_LOCK_UNLOCK);
/*
* Check here, as calling loops will have locks held, preventing
* interrupts from being processed.
*/
CHECK_FOR_INTERRUPTS();
/*
* If the leaf page still has a parent pointing to it (or a chain of
* parents), we don't unlink the leaf page yet, but the topmost remaining
* parent in the branch. Set 'target' and 'buf' to reference the page
* actually being unlinked.
*/
target = BTreeTupleGetTopParent(leafhikey);
if (target != InvalidBlockNumber)
{
Assert(target != leafblkno);
/* fetch the block number of the topmost parent's left sibling */
buf = _bt_getbuf(rel, target, BT_READ);
page = BufferGetPage(buf);
opaque = (BTPageOpaque) PageGetSpecialPointer(page);
leftsib = opaque->btpo_prev;
targetlevel = opaque->btpo.level;
/*
* To avoid deadlocks, we'd better drop the target page lock before
* going further.
*/
LockBuffer(buf, BUFFER_LOCK_UNLOCK);
}
else
{
target = leafblkno;
buf = leafbuf;
leftsib = leafleftsib;
targetlevel = 0;
}
/*
* We have to lock the pages we need to modify in the standard order:
* moving right, then up. Else we will deadlock against other writers.
*
* So, first lock the leaf page, if it's not the target. Then find and
* write-lock the current left sibling of the target page. The sibling
* that was current a moment ago could have split, so we may have to move
* right. This search could fail if either the sibling or the target page
* was deleted by someone else meanwhile; if so, give up. (Right now,
* that should never happen, since page deletion is only done in VACUUM
* and there shouldn't be multiple VACUUMs concurrently on the same
* table.)
*/
if (target != leafblkno)
LockBuffer(leafbuf, BT_WRITE);
if (leftsib != P_NONE)
{
lbuf = _bt_getbuf(rel, leftsib, BT_WRITE);
page = BufferGetPage(lbuf);
opaque = (BTPageOpaque) PageGetSpecialPointer(page);
while (P_ISDELETED(opaque) || opaque->btpo_next != target)
{
/* step right one page */
leftsib = opaque->btpo_next;
_bt_relbuf(rel, lbuf);
/*
* It'd be good to check for interrupts here, but it's not easy to
* do so because a lock is always held. This block isn't
* frequently reached, so hopefully the consequences of not
* checking interrupts aren't too bad.
*/
if (leftsib == P_NONE)
{
elog(LOG, "no left sibling (concurrent deletion?) of block %u in \"%s\"",
target,
RelationGetRelationName(rel));
if (target != leafblkno)
{
/* we have only a pin on target, but pin+lock on leafbuf */
ReleaseBuffer(buf);
_bt_relbuf(rel, leafbuf);
}
else
{
/* we have only a pin on leafbuf */
ReleaseBuffer(leafbuf);
}
return false;
}
lbuf = _bt_getbuf(rel, leftsib, BT_WRITE);
page = BufferGetPage(lbuf);
opaque = (BTPageOpaque) PageGetSpecialPointer(page);
}
}
else
lbuf = InvalidBuffer;
/*
* Next write-lock the target page itself. It should be okay to take just
* a write lock not a superexclusive lock, since no scans would stop on an
* empty page.
*/
LockBuffer(buf, BT_WRITE);
page = BufferGetPage(buf);
opaque = (BTPageOpaque) PageGetSpecialPointer(page);
/*
* Check page is still empty etc, else abandon deletion. This is just for
* paranoia's sake; a half-dead page cannot resurrect because there can be
* only one vacuum process running at a time.
*/
if (P_RIGHTMOST(opaque) || P_ISROOT(opaque) || P_ISDELETED(opaque))
{
elog(ERROR, "half-dead page changed status unexpectedly in block %u of index \"%s\"",
target, RelationGetRelationName(rel));
}
if (opaque->btpo_prev != leftsib)
elog(ERROR, "left link changed unexpectedly in block %u of index \"%s\"",
target, RelationGetRelationName(rel));
if (target == leafblkno)
{
if (P_FIRSTDATAKEY(opaque) <= PageGetMaxOffsetNumber(page) ||
!P_ISLEAF(opaque) || !P_ISHALFDEAD(opaque))
elog(ERROR, "half-dead page changed status unexpectedly in block %u of index \"%s\"",
target, RelationGetRelationName(rel));
nextchild = InvalidBlockNumber;
}
else
{
if (P_FIRSTDATAKEY(opaque) != PageGetMaxOffsetNumber(page) ||
P_ISLEAF(opaque))
elog(ERROR, "half-dead page changed status unexpectedly in block %u of index \"%s\"",
target, RelationGetRelationName(rel));
/* remember the next non-leaf child down in the branch. */
itemid = PageGetItemId(page, P_FIRSTDATAKEY(opaque));
nextchild = BTreeInnerTupleGetDownLink((IndexTuple) PageGetItem(page, itemid));
if (nextchild == leafblkno)
nextchild = InvalidBlockNumber;
}
/*
* And next write-lock the (current) right sibling.
*/
rightsib = opaque->btpo_next;
rbuf = _bt_getbuf(rel, rightsib, BT_WRITE);
page = BufferGetPage(rbuf);
opaque = (BTPageOpaque) PageGetSpecialPointer(page);
if (opaque->btpo_prev != target)
elog(ERROR, "right sibling's left-link doesn't match: "
"block %u links to %u instead of expected %u in index \"%s\"",
rightsib, opaque->btpo_prev, target,
RelationGetRelationName(rel));
rightsib_is_rightmost = P_RIGHTMOST(opaque);
*rightsib_empty = (P_FIRSTDATAKEY(opaque) > PageGetMaxOffsetNumber(page));
/*
* If we are deleting the next-to-last page on the target's level, then
* the rightsib is a candidate to become the new fast root. (In theory, it
* might be possible to push the fast root even further down, but the odds
* of doing so are slim, and the locking considerations daunting.)
*
* We don't support handling this in the case where the parent is becoming
* half-dead, even though it theoretically could occur.
*
* We can safely acquire a lock on the metapage here --- see comments for
* _bt_newroot().
*/
if (leftsib == P_NONE && rightsib_is_rightmost)
{
page = BufferGetPage(rbuf);
opaque = (BTPageOpaque) PageGetSpecialPointer(page);
if (P_RIGHTMOST(opaque))
{
/* rightsib will be the only one left on the level */
metabuf = _bt_getbuf(rel, BTREE_METAPAGE, BT_WRITE);
metapg = BufferGetPage(metabuf);
metad = BTPageGetMeta(metapg);
/*
* The expected case here is btm_fastlevel == targetlevel+1; if
* the fastlevel is <= targetlevel, something is wrong, and we
* choose to overwrite it to fix it.
*/
if (metad->btm_fastlevel > targetlevel + 1)
{
/* no update wanted */
_bt_relbuf(rel, metabuf);
metabuf = InvalidBuffer;
}
}
}
/*
* Here we begin doing the deletion.
*/
/* No ereport(ERROR) until changes are logged */
START_CRIT_SECTION();
/*
* Update siblings' side-links. Note the target page's side-links will
* continue to point to the siblings. Asserts here are just rechecking
* things we already verified above.
*/
if (BufferIsValid(lbuf))
{
page = BufferGetPage(lbuf);
opaque = (BTPageOpaque) PageGetSpecialPointer(page);
Assert(opaque->btpo_next == target);
opaque->btpo_next = rightsib;
}
page = BufferGetPage(rbuf);
opaque = (BTPageOpaque) PageGetSpecialPointer(page);
Assert(opaque->btpo_prev == target);
opaque->btpo_prev = leftsib;
/*
* If we deleted a parent of the targeted leaf page, instead of the leaf
* itself, update the leaf to point to the next remaining child in the
* branch.
*/
if (target != leafblkno)
BTreeTupleSetTopParent(leafhikey, nextchild);
/*
* Mark the page itself deleted. It can be recycled when all current
* transactions are gone. Storing GetTopTransactionId() would work, but
* we're in VACUUM and would not otherwise have an XID. Having already
* updated links to the target, ReadNewTransactionId() suffices as an
* upper bound. Any scan having retained a now-stale link is advertising
* in its PGXACT an xmin less than or equal to the value we read here. It
* will continue to do so, holding back RecentGlobalXmin, for the duration
* of that scan.
*/
page = BufferGetPage(buf);
opaque = (BTPageOpaque) PageGetSpecialPointer(page);
opaque->btpo_flags &= ~BTP_HALF_DEAD;
opaque->btpo_flags |= BTP_DELETED;
opaque->btpo.xact = ReadNewTransactionId();
/* And update the metapage, if needed */
if (BufferIsValid(metabuf))
{
/* upgrade metapage if needed */
if (metad->btm_version < BTREE_NOVAC_VERSION)
_bt_upgrademetapage(metapg);
metad->btm_fastroot = rightsib;
metad->btm_fastlevel = targetlevel;
MarkBufferDirty(metabuf);
}
/* Must mark buffers dirty before XLogInsert */
MarkBufferDirty(rbuf);
MarkBufferDirty(buf);
if (BufferIsValid(lbuf))
MarkBufferDirty(lbuf);
if (target != leafblkno)
MarkBufferDirty(leafbuf);
/* XLOG stuff */
if (RelationNeedsWAL(rel))
{
xl_btree_unlink_page xlrec;
xl_btree_metadata xlmeta;
uint8 xlinfo;
XLogRecPtr recptr;
XLogBeginInsert();
XLogRegisterBuffer(0, buf, REGBUF_WILL_INIT);
if (BufferIsValid(lbuf))
XLogRegisterBuffer(1, lbuf, REGBUF_STANDARD);
XLogRegisterBuffer(2, rbuf, REGBUF_STANDARD);
if (target != leafblkno)
XLogRegisterBuffer(3, leafbuf, REGBUF_WILL_INIT);
/* information on the unlinked block */
xlrec.leftsib = leftsib;
xlrec.rightsib = rightsib;
xlrec.btpo_xact = opaque->btpo.xact;
/* information needed to recreate the leaf block (if not the target) */
xlrec.leafleftsib = leafleftsib;
xlrec.leafrightsib = leafrightsib;
xlrec.topparent = nextchild;
XLogRegisterData((char *) &xlrec, SizeOfBtreeUnlinkPage);
if (BufferIsValid(metabuf))
{
XLogRegisterBuffer(4, metabuf, REGBUF_WILL_INIT | REGBUF_STANDARD);
Assert(metad->btm_version >= BTREE_NOVAC_VERSION);
xlmeta.version = metad->btm_version;
xlmeta.root = metad->btm_root;
xlmeta.level = metad->btm_level;
xlmeta.fastroot = metad->btm_fastroot;
xlmeta.fastlevel = metad->btm_fastlevel;
xlmeta.oldest_btpo_xact = metad->btm_oldest_btpo_xact;
xlmeta.last_cleanup_num_heap_tuples = metad->btm_last_cleanup_num_heap_tuples;
XLogRegisterBufData(4, (char *) &xlmeta, sizeof(xl_btree_metadata));
xlinfo = XLOG_BTREE_UNLINK_PAGE_META;
}
else
xlinfo = XLOG_BTREE_UNLINK_PAGE;
recptr = XLogInsert(RM_BTREE_ID, xlinfo);
if (BufferIsValid(metabuf))
{
PageSetLSN(metapg, recptr);
}
page = BufferGetPage(rbuf);
PageSetLSN(page, recptr);
page = BufferGetPage(buf);
PageSetLSN(page, recptr);
if (BufferIsValid(lbuf))
{
page = BufferGetPage(lbuf);
PageSetLSN(page, recptr);
}
if (target != leafblkno)
{
page = BufferGetPage(leafbuf);
PageSetLSN(page, recptr);
}
}
END_CRIT_SECTION();
/* release metapage */
if (BufferIsValid(metabuf))
_bt_relbuf(rel, metabuf);
/* release siblings */
if (BufferIsValid(lbuf))
_bt_relbuf(rel, lbuf);
_bt_relbuf(rel, rbuf);
/*
* Release the target, if it was not the leaf block. The leaf is always
* kept locked.
*/
if (target != leafblkno)
_bt_relbuf(rel, buf);
return true;
}
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