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postgresql/src/backend/access/hash/hashpage.c

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/*-------------------------------------------------------------------------
*
* hashpage.c
* Hash table page management code for the Postgres hash 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/hash/hashpage.c,v 1.29 2001/01/24 19:42:47 momjian Exp $
*
* NOTES
* Postgres hash pages look like ordinary relation pages. The opaque
* data at high addresses includes information about the page including
* whether a page is an overflow page or a true bucket, the block
* numbers of the preceding and following pages, and the overflow
* address of the page if it is an overflow page.
*
* The first page in a hash relation, page zero, is special -- it stores
* information describing the hash table; it is referred to as teh
* "meta page." Pages one and higher store the actual data.
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "access/genam.h"
#include "access/hash.h"
#include "miscadmin.h"
#include "storage/lmgr.h"
static void _hash_setpagelock(Relation rel, BlockNumber blkno, int access);
static void _hash_unsetpagelock(Relation rel, BlockNumber blkno, int access);
static void _hash_splitpage(Relation rel, Buffer metabuf, Bucket obucket, Bucket nbucket);
/*
* We use high-concurrency locking on hash indices. There are two cases in
* which we don't do locking. One is when we're building the index.
* 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.
*/
#define USELOCKING (!BuildingHash && !IsInitProcessingMode())
/*
* _hash_metapinit() -- Initialize the metadata page of a hash index,
* the two buckets that we begin with and the initial
* bitmap page.
*/
void
_hash_metapinit(Relation rel)
{
HashMetaPage metap;
HashPageOpaque pageopaque;
Buffer metabuf;
Buffer buf;
Page pg;
int nbuckets;
uint32 nelem; /* number elements */
uint32 lg2nelem; /* _hash_log2(nelem) */
uint32 nblocks;
uint16 i;
/* can't be sharing this with anyone, now... */
if (USELOCKING)
LockRelation(rel, AccessExclusiveLock);
if ((nblocks = RelationGetNumberOfBlocks(rel)) != 0)
{
elog(ERROR, "Cannot initialize non-empty hash table %s",
RelationGetRelationName(rel));
}
metabuf = _hash_getbuf(rel, HASH_METAPAGE, HASH_WRITE);
pg = BufferGetPage(metabuf);
metap = (HashMetaPage) pg;
_hash_pageinit(pg, BufferGetPageSize(metabuf));
metap->hashm_magic = HASH_MAGIC;
metap->hashm_version = HASH_VERSION;
metap->hashm_nkeys = 0;
metap->hashm_nmaps = 0;
metap->hashm_ffactor = DEFAULT_FFACTOR;
metap->hashm_bsize = BufferGetPageSize(metabuf);
metap->hashm_bshift = _hash_log2(metap->hashm_bsize);
for (i = metap->hashm_bshift; i > 0; --i)
{
if ((1 << i) < (metap->hashm_bsize -
(MAXALIGN(sizeof(PageHeaderData)) +
MAXALIGN(sizeof(HashPageOpaqueData)))))
break;
}
Assert(i);
metap->hashm_bmsize = 1 << i;
metap->hashm_procid = index_getprocid(rel, 1, HASHPROC);
/*
* Make nelem = 2 rather than 0 so that we end up allocating space for
* the next greater power of two number of buckets.
*/
nelem = 2;
lg2nelem = 1; /* _hash_log2(MAX(nelem, 2)) */
nbuckets = 2; /* 1 << lg2nelem */
MemSet((char *) metap->hashm_spares, 0, sizeof(metap->hashm_spares));
MemSet((char *) metap->hashm_mapp, 0, sizeof(metap->hashm_mapp));
metap->hashm_spares[lg2nelem] = 2; /* lg2nelem + 1 */
metap->hashm_spares[lg2nelem + 1] = 2; /* lg2nelem + 1 */
metap->hashm_ovflpoint = 1; /* lg2nelem */
metap->hashm_lastfreed = 2;
metap->hashm_maxbucket = metap->hashm_lowmask = 1; /* nbuckets - 1 */
metap->hashm_highmask = 3; /* (nbuckets << 1) - 1 */
pageopaque = (HashPageOpaque) PageGetSpecialPointer(pg);
pageopaque->hasho_oaddr = InvalidOvflAddress;
pageopaque->hasho_prevblkno = InvalidBlockNumber;
pageopaque->hasho_nextblkno = InvalidBlockNumber;
pageopaque->hasho_flag = LH_META_PAGE;
pageopaque->hasho_bucket = -1;
/*
* First bitmap page is at: splitpoint lg2nelem page offset 1 which
* turns out to be page 3. Couldn't initialize page 3 until we
* created the first two buckets above.
*/
if (_hash_initbitmap(rel, metap, OADDR_OF(lg2nelem, 1), lg2nelem + 1, 0))
elog(ERROR, "Problem with _hash_initbitmap.");
/* all done */
_hash_wrtnorelbuf(rel, metabuf);
/*
* initialize the first two buckets
*/
for (i = 0; i <= 1; i++)
{
buf = _hash_getbuf(rel, BUCKET_TO_BLKNO(i), HASH_WRITE);
pg = BufferGetPage(buf);
_hash_pageinit(pg, BufferGetPageSize(buf));
pageopaque = (HashPageOpaque) PageGetSpecialPointer(pg);
pageopaque->hasho_oaddr = InvalidOvflAddress;
pageopaque->hasho_prevblkno = InvalidBlockNumber;
pageopaque->hasho_nextblkno = InvalidBlockNumber;
pageopaque->hasho_flag = LH_BUCKET_PAGE;
pageopaque->hasho_bucket = i;
_hash_wrtbuf(rel, buf);
}
_hash_relbuf(rel, metabuf, HASH_WRITE);
if (USELOCKING)
UnlockRelation(rel, AccessExclusiveLock);
}
/*
* _hash_getbuf() -- Get a buffer by block number for read or write.
*
* When this routine returns, the appropriate lock is set on the
* requested buffer its reference count is correct.
*
* XXX P_NEW is not used because, unlike the tree structures, we
* need the bucket blocks to be at certain block numbers. we must
* depend on the caller to call _hash_pageinit on the block if it
* knows that this is a new block.
*/
Buffer
_hash_getbuf(Relation rel, BlockNumber blkno, int access)
{
Buffer buf;
if (blkno == P_NEW)
elog(ERROR, "_hash_getbuf: internal error: hash AM does not use P_NEW");
switch (access)
{
case HASH_WRITE:
case HASH_READ:
_hash_setpagelock(rel, blkno, access);
break;
default:
elog(ERROR, "_hash_getbuf: invalid access (%d) on new blk: %s",
access, RelationGetRelationName(rel));
break;
}
buf = ReadBuffer(rel, blkno);
/* ref count and lock type are correct */
return buf;
}
/*
* _hash_relbuf() -- release a locked buffer.
*/
void
_hash_relbuf(Relation rel, Buffer buf, int access)
{
BlockNumber blkno;
blkno = BufferGetBlockNumber(buf);
switch (access)
{
case HASH_WRITE:
case HASH_READ:
_hash_unsetpagelock(rel, blkno, access);
break;
default:
elog(ERROR, "_hash_relbuf: invalid access (%d) on blk %x: %s",
access, blkno, RelationGetRelationName(rel));
}
ReleaseBuffer(buf);
}
/*
* _hash_wrtbuf() -- write a hash page to disk.
*
* This routine releases the lock held on the buffer and our reference
* to it. It is an error to call _hash_wrtbuf() without a write lock
* or a reference to the buffer.
*/
void
_hash_wrtbuf(Relation rel, Buffer buf)
{
BlockNumber blkno;
blkno = BufferGetBlockNumber(buf);
WriteBuffer(buf);
_hash_unsetpagelock(rel, blkno, HASH_WRITE);
}
/*
* _hash_wrtnorelbuf() -- write a hash page to disk, but do not release
* our reference or lock.
*
* It is an error to call _hash_wrtnorelbuf() without a write lock
* or a reference to the buffer.
*/
void
_hash_wrtnorelbuf(Relation rel, Buffer buf)
{
BlockNumber blkno;
blkno = BufferGetBlockNumber(buf);
WriteNoReleaseBuffer(buf);
}
Page
_hash_chgbufaccess(Relation rel,
Buffer *bufp,
int from_access,
int to_access)
{
BlockNumber blkno;
blkno = BufferGetBlockNumber(*bufp);
switch (from_access)
{
case HASH_WRITE:
_hash_wrtbuf(rel, *bufp);
break;
case HASH_READ:
_hash_relbuf(rel, *bufp, from_access);
break;
default:
elog(ERROR, "_hash_chgbufaccess: invalid access (%d) on blk %x: %s",
from_access, blkno, RelationGetRelationName(rel));
break;
}
*bufp = _hash_getbuf(rel, blkno, to_access);
return BufferGetPage(*bufp);
}
/*
* _hash_pageinit() -- Initialize a new page.
*/
void
_hash_pageinit(Page page, Size size)
{
Assert(((PageHeader) page)->pd_lower == 0);
Assert(((PageHeader) page)->pd_upper == 0);
Assert(((PageHeader) page)->pd_special == 0);
/*
* 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(HashPageOpaqueData));
}
static void
_hash_setpagelock(Relation rel,
BlockNumber blkno,
int access)
{
if (USELOCKING)
{
switch (access)
{
case HASH_WRITE:
LockPage(rel, blkno, ExclusiveLock);
break;
case HASH_READ:
LockPage(rel, blkno, ShareLock);
break;
default:
elog(ERROR, "_hash_setpagelock: invalid access (%d) on blk %x: %s",
access, blkno, RelationGetRelationName(rel));
break;
}
}
}
static void
_hash_unsetpagelock(Relation rel,
BlockNumber blkno,
int access)
{
if (USELOCKING)
{
switch (access)
{
case HASH_WRITE:
UnlockPage(rel, blkno, ExclusiveLock);
break;
case HASH_READ:
UnlockPage(rel, blkno, ShareLock);
break;
default:
elog(ERROR, "_hash_unsetpagelock: invalid access (%d) on blk %x: %s",
access, blkno, RelationGetRelationName(rel));
break;
}
}
}
void
_hash_pagedel(Relation rel, ItemPointer tid)
{
Buffer buf;
Buffer metabuf;
Page page;
BlockNumber blkno;
OffsetNumber offno;
HashMetaPage metap;
HashPageOpaque opaque;
blkno = ItemPointerGetBlockNumber(tid);
offno = ItemPointerGetOffsetNumber(tid);
buf = _hash_getbuf(rel, blkno, HASH_WRITE);
page = BufferGetPage(buf);
_hash_checkpage(page, LH_BUCKET_PAGE | LH_OVERFLOW_PAGE);
opaque = (HashPageOpaque) PageGetSpecialPointer(page);
PageIndexTupleDelete(page, offno);
_hash_wrtnorelbuf(rel, buf);
if (PageIsEmpty(page) && (opaque->hasho_flag & LH_OVERFLOW_PAGE))
{
buf = _hash_freeovflpage(rel, buf);
if (BufferIsValid(buf))
_hash_relbuf(rel, buf, HASH_WRITE);
}
else
_hash_relbuf(rel, buf, HASH_WRITE);
metabuf = _hash_getbuf(rel, HASH_METAPAGE, HASH_WRITE);
metap = (HashMetaPage) BufferGetPage(metabuf);
_hash_checkpage((Page) metap, LH_META_PAGE);
++metap->hashm_nkeys;
_hash_wrtbuf(rel, metabuf);
}
void
_hash_expandtable(Relation rel, Buffer metabuf)
{
HashMetaPage metap;
Bucket old_bucket;
Bucket new_bucket;
uint32 spare_ndx;
/* elog(DEBUG, "_hash_expandtable: expanding..."); */
metap = (HashMetaPage) BufferGetPage(metabuf);
_hash_checkpage((Page) metap, LH_META_PAGE);
metap = (HashMetaPage) _hash_chgbufaccess(rel, &metabuf, HASH_READ, HASH_WRITE);
new_bucket = ++metap->MAX_BUCKET;
metap = (HashMetaPage) _hash_chgbufaccess(rel, &metabuf, HASH_WRITE, HASH_READ);
old_bucket = (metap->MAX_BUCKET & metap->LOW_MASK);
/*
* If the split point is increasing (MAX_BUCKET's log base 2 *
* increases), we need to copy the current contents of the spare split
* bucket to the next bucket.
*/
spare_ndx = _hash_log2(metap->MAX_BUCKET + 1);
if (spare_ndx > metap->OVFL_POINT)
{
metap = (HashMetaPage) _hash_chgbufaccess(rel, &metabuf, HASH_READ, HASH_WRITE);
metap->SPARES[spare_ndx] = metap->SPARES[metap->OVFL_POINT];
metap->OVFL_POINT = spare_ndx;
metap = (HashMetaPage) _hash_chgbufaccess(rel, &metabuf, HASH_WRITE, HASH_READ);
}
if (new_bucket > metap->HIGH_MASK)
{
/* Starting a new doubling */
metap = (HashMetaPage) _hash_chgbufaccess(rel, &metabuf, HASH_READ, HASH_WRITE);
metap->LOW_MASK = metap->HIGH_MASK;
metap->HIGH_MASK = new_bucket | metap->LOW_MASK;
metap = (HashMetaPage) _hash_chgbufaccess(rel, &metabuf, HASH_WRITE, HASH_READ);
}
/* Relocate records to the new bucket */
_hash_splitpage(rel, metabuf, old_bucket, new_bucket);
}
/*
* _hash_splitpage -- split 'obucket' into 'obucket' and 'nbucket'
*
* this routine is actually misnamed -- we are splitting a bucket that
* consists of a base bucket page and zero or more overflow (bucket
* chain) pages.
*/
static void
_hash_splitpage(Relation rel,
Buffer metabuf,
Bucket obucket,
Bucket nbucket)
{
Bucket bucket;
Buffer obuf;
Buffer nbuf;
Buffer ovflbuf;
BlockNumber oblkno;
BlockNumber nblkno;
bool null;
Datum datum;
HashItem hitem;
HashPageOpaque oopaque;
HashPageOpaque nopaque;
HashMetaPage metap;
IndexTuple itup;
Size itemsz;
OffsetNumber ooffnum;
OffsetNumber noffnum;
OffsetNumber omaxoffnum;
Page opage;
Page npage;
TupleDesc itupdesc;
/* elog(DEBUG, "_hash_splitpage: splitting %d into %d,%d",
obucket, obucket, nbucket);
*/
metap = (HashMetaPage) BufferGetPage(metabuf);
_hash_checkpage((Page) metap, LH_META_PAGE);
/* get the buffers & pages */
oblkno = BUCKET_TO_BLKNO(obucket);
nblkno = BUCKET_TO_BLKNO(nbucket);
obuf = _hash_getbuf(rel, oblkno, HASH_WRITE);
nbuf = _hash_getbuf(rel, nblkno, HASH_WRITE);
opage = BufferGetPage(obuf);
npage = BufferGetPage(nbuf);
/* initialize the new bucket */
_hash_pageinit(npage, BufferGetPageSize(nbuf));
nopaque = (HashPageOpaque) PageGetSpecialPointer(npage);
nopaque->hasho_prevblkno = InvalidBlockNumber;
nopaque->hasho_nextblkno = InvalidBlockNumber;
nopaque->hasho_flag = LH_BUCKET_PAGE;
nopaque->hasho_oaddr = InvalidOvflAddress;
nopaque->hasho_bucket = nbucket;
_hash_wrtnorelbuf(rel, nbuf);
/*
* make sure the old bucket isn't empty. advance 'opage' and friends
* through the overflow bucket chain until we find a non-empty page.
*
* XXX we should only need this once, if we are careful to preserve the
* invariant that overflow pages are never empty.
*/
_hash_checkpage(opage, LH_BUCKET_PAGE);
oopaque = (HashPageOpaque) PageGetSpecialPointer(opage);
if (PageIsEmpty(opage))
{
oblkno = oopaque->hasho_nextblkno;
_hash_relbuf(rel, obuf, HASH_WRITE);
if (!BlockNumberIsValid(oblkno))
{
/*
* the old bucket is completely empty; of course, the new
* bucket will be as well, but since it's a base bucket page
* we don't care.
*/
_hash_relbuf(rel, nbuf, HASH_WRITE);
return;
}
obuf = _hash_getbuf(rel, oblkno, HASH_WRITE);
opage = BufferGetPage(obuf);
_hash_checkpage(opage, LH_OVERFLOW_PAGE);
if (PageIsEmpty(opage))
elog(ERROR, "_hash_splitpage: empty overflow page %d", oblkno);
oopaque = (HashPageOpaque) PageGetSpecialPointer(opage);
}
/*
* we are now guaranteed that 'opage' is not empty. partition the
* tuples in the old bucket between the old bucket and the new bucket,
* advancing along their respective overflow bucket chains and adding
* overflow pages as needed.
*/
ooffnum = FirstOffsetNumber;
omaxoffnum = PageGetMaxOffsetNumber(opage);
for (;;)
{
/*
* at each iteration through this loop, each of these variables
* should be up-to-date: obuf opage oopaque ooffnum omaxoffnum
*/
/* check if we're at the end of the page */
if (ooffnum > omaxoffnum)
{
/* at end of page, but check for overflow page */
oblkno = oopaque->hasho_nextblkno;
if (BlockNumberIsValid(oblkno))
{
/*
* we ran out of tuples on this particular page, but we
* have more overflow pages; re-init values.
*/
_hash_wrtbuf(rel, obuf);
obuf = _hash_getbuf(rel, oblkno, HASH_WRITE);
opage = BufferGetPage(obuf);
_hash_checkpage(opage, LH_OVERFLOW_PAGE);
oopaque = (HashPageOpaque) PageGetSpecialPointer(opage);
/* we're guaranteed that an ovfl page has at least 1 tuple */
if (PageIsEmpty(opage))
{
elog(ERROR, "_hash_splitpage: empty ovfl page %d!",
oblkno);
}
ooffnum = FirstOffsetNumber;
omaxoffnum = PageGetMaxOffsetNumber(opage);
}
else
{
/*
* we're at the end of the bucket chain, so now we're
* really done with everything. before quitting, call
* _hash_squeezebucket to ensure the tuples in the bucket
* (including the overflow pages) are packed as tightly as
* possible.
*/
_hash_wrtbuf(rel, obuf);
_hash_wrtbuf(rel, nbuf);
_hash_squeezebucket(rel, metap, obucket);
return;
}
}
/* hash on the tuple */
hitem = (HashItem) PageGetItem(opage, PageGetItemId(opage, ooffnum));
itup = &(hitem->hash_itup);
itupdesc = RelationGetDescr(rel);
datum = index_getattr(itup, 1, itupdesc, &null);
bucket = _hash_call(rel, metap, datum);
if (bucket == nbucket)
{
/*
* insert the tuple into the new bucket. if it doesn't fit on
* the current page in the new bucket, we must allocate a new
* overflow page and place the tuple on that page instead.
*/
itemsz = IndexTupleDSize(hitem->hash_itup)
+ (sizeof(HashItemData) - sizeof(IndexTupleData));
itemsz = MAXALIGN(itemsz);
if (PageGetFreeSpace(npage) < itemsz)
{
ovflbuf = _hash_addovflpage(rel, &metabuf, nbuf);
_hash_wrtbuf(rel, nbuf);
nbuf = ovflbuf;
npage = BufferGetPage(nbuf);
_hash_checkpage(npage, LH_BUCKET_PAGE | LH_OVERFLOW_PAGE);
}
noffnum = OffsetNumberNext(PageGetMaxOffsetNumber(npage));
PageAddItem(npage, (Item) hitem, itemsz, noffnum, LP_USED);
_hash_wrtnorelbuf(rel, nbuf);
/*
* now delete the tuple from the old bucket. after this
* section of code, 'ooffnum' will actually point to the
* ItemId to which we would point if we had advanced it before
* the deletion (PageIndexTupleDelete repacks the ItemId
* array). this also means that 'omaxoffnum' is exactly one
* less than it used to be, so we really can just decrement it
* instead of calling PageGetMaxOffsetNumber.
*/
PageIndexTupleDelete(opage, ooffnum);
_hash_wrtnorelbuf(rel, obuf);
omaxoffnum = OffsetNumberPrev(omaxoffnum);
/*
* tidy up. if the old page was an overflow page and it is
* now empty, we must free it (we want to preserve the
* invariant that overflow pages cannot be empty).
*/
if (PageIsEmpty(opage) &&
(oopaque->hasho_flag & LH_OVERFLOW_PAGE))
{
obuf = _hash_freeovflpage(rel, obuf);
/* check that we're not through the bucket chain */
if (BufferIsInvalid(obuf))
{
_hash_wrtbuf(rel, nbuf);
_hash_squeezebucket(rel, metap, obucket);
return;
}
/*
* re-init. again, we're guaranteed that an ovfl page has
* at least one tuple.
*/
opage = BufferGetPage(obuf);
_hash_checkpage(opage, LH_OVERFLOW_PAGE);
oblkno = BufferGetBlockNumber(obuf);
oopaque = (HashPageOpaque) PageGetSpecialPointer(opage);
if (PageIsEmpty(opage))
{
elog(ERROR, "_hash_splitpage: empty overflow page %d",
oblkno);
}
ooffnum = FirstOffsetNumber;
omaxoffnum = PageGetMaxOffsetNumber(opage);
}
}
else
{
/*
* the tuple stays on this page. we didn't move anything, so
* we didn't delete anything and therefore we don't have to
* change 'omaxoffnum'.
*
* XXX any hash value from [0, nbucket-1] will map to this
* bucket, which doesn't make sense to me.
*/
ooffnum = OffsetNumberNext(ooffnum);
}
}
/* NOTREACHED */
}
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