762 lines
22 KiB
C
762 lines
22 KiB
C
/*-------------------------------------------------------------------------
|
|
*
|
|
* hashovfl.c
|
|
* Overflow page management code for the Postgres hash access method
|
|
*
|
|
* Portions Copyright (c) 1996-2016, PostgreSQL Global Development Group
|
|
* Portions Copyright (c) 1994, Regents of the University of California
|
|
*
|
|
*
|
|
* IDENTIFICATION
|
|
* src/backend/access/hash/hashovfl.c
|
|
*
|
|
* NOTES
|
|
* Overflow pages look like ordinary relation pages.
|
|
*
|
|
*-------------------------------------------------------------------------
|
|
*/
|
|
#include "postgres.h"
|
|
|
|
#include "access/hash.h"
|
|
#include "utils/rel.h"
|
|
|
|
|
|
static Buffer _hash_getovflpage(Relation rel, Buffer metabuf);
|
|
static uint32 _hash_firstfreebit(uint32 map);
|
|
|
|
|
|
/*
|
|
* Convert overflow page bit number (its index in the free-page bitmaps)
|
|
* to block number within the index.
|
|
*/
|
|
static BlockNumber
|
|
bitno_to_blkno(HashMetaPage metap, uint32 ovflbitnum)
|
|
{
|
|
uint32 splitnum = metap->hashm_ovflpoint;
|
|
uint32 i;
|
|
|
|
/* Convert zero-based bitnumber to 1-based page number */
|
|
ovflbitnum += 1;
|
|
|
|
/* Determine the split number for this page (must be >= 1) */
|
|
for (i = 1;
|
|
i < splitnum && ovflbitnum > metap->hashm_spares[i];
|
|
i++)
|
|
/* loop */ ;
|
|
|
|
/*
|
|
* Convert to absolute page number by adding the number of bucket pages
|
|
* that exist before this split point.
|
|
*/
|
|
return (BlockNumber) ((1 << i) + ovflbitnum);
|
|
}
|
|
|
|
/*
|
|
* Convert overflow page block number to bit number for free-page bitmap.
|
|
*/
|
|
static uint32
|
|
blkno_to_bitno(HashMetaPage metap, BlockNumber ovflblkno)
|
|
{
|
|
uint32 splitnum = metap->hashm_ovflpoint;
|
|
uint32 i;
|
|
uint32 bitnum;
|
|
|
|
/* Determine the split number containing this page */
|
|
for (i = 1; i <= splitnum; i++)
|
|
{
|
|
if (ovflblkno <= (BlockNumber) (1 << i))
|
|
break; /* oops */
|
|
bitnum = ovflblkno - (1 << i);
|
|
if (bitnum <= metap->hashm_spares[i])
|
|
return bitnum - 1; /* -1 to convert 1-based to 0-based */
|
|
}
|
|
|
|
elog(ERROR, "invalid overflow block number %u", ovflblkno);
|
|
return 0; /* keep compiler quiet */
|
|
}
|
|
|
|
/*
|
|
* _hash_addovflpage
|
|
*
|
|
* Add an overflow page to the bucket whose last page is pointed to by 'buf'.
|
|
*
|
|
* On entry, the caller must hold a pin but no lock on 'buf'. The pin is
|
|
* dropped before exiting (we assume the caller is not interested in 'buf'
|
|
* anymore). The returned overflow page will be pinned and write-locked;
|
|
* it is guaranteed to be empty.
|
|
*
|
|
* The caller must hold a pin, but no lock, on the metapage buffer.
|
|
* That buffer is returned in the same state.
|
|
*
|
|
* The caller must hold at least share lock on the bucket, to ensure that
|
|
* no one else tries to compact the bucket meanwhile. This guarantees that
|
|
* 'buf' won't stop being part of the bucket while it's unlocked.
|
|
*
|
|
* NB: since this could be executed concurrently by multiple processes,
|
|
* one should not assume that the returned overflow page will be the
|
|
* immediate successor of the originally passed 'buf'. Additional overflow
|
|
* pages might have been added to the bucket chain in between.
|
|
*/
|
|
Buffer
|
|
_hash_addovflpage(Relation rel, Buffer metabuf, Buffer buf)
|
|
{
|
|
Buffer ovflbuf;
|
|
Page page;
|
|
Page ovflpage;
|
|
HashPageOpaque pageopaque;
|
|
HashPageOpaque ovflopaque;
|
|
|
|
/* allocate and lock an empty overflow page */
|
|
ovflbuf = _hash_getovflpage(rel, metabuf);
|
|
|
|
/*
|
|
* Write-lock the tail page. It is okay to hold two buffer locks here
|
|
* since there cannot be anyone else contending for access to ovflbuf.
|
|
*/
|
|
_hash_chgbufaccess(rel, buf, HASH_NOLOCK, HASH_WRITE);
|
|
|
|
/* probably redundant... */
|
|
_hash_checkpage(rel, buf, LH_BUCKET_PAGE | LH_OVERFLOW_PAGE);
|
|
|
|
/* loop to find current tail page, in case someone else inserted too */
|
|
for (;;)
|
|
{
|
|
BlockNumber nextblkno;
|
|
|
|
page = BufferGetPage(buf);
|
|
pageopaque = (HashPageOpaque) PageGetSpecialPointer(page);
|
|
nextblkno = pageopaque->hasho_nextblkno;
|
|
|
|
if (!BlockNumberIsValid(nextblkno))
|
|
break;
|
|
|
|
/* we assume we do not need to write the unmodified page */
|
|
_hash_relbuf(rel, buf);
|
|
|
|
buf = _hash_getbuf(rel, nextblkno, HASH_WRITE, LH_OVERFLOW_PAGE);
|
|
}
|
|
|
|
/* now that we have correct backlink, initialize new overflow page */
|
|
ovflpage = BufferGetPage(ovflbuf);
|
|
ovflopaque = (HashPageOpaque) PageGetSpecialPointer(ovflpage);
|
|
ovflopaque->hasho_prevblkno = BufferGetBlockNumber(buf);
|
|
ovflopaque->hasho_nextblkno = InvalidBlockNumber;
|
|
ovflopaque->hasho_bucket = pageopaque->hasho_bucket;
|
|
ovflopaque->hasho_flag = LH_OVERFLOW_PAGE;
|
|
ovflopaque->hasho_page_id = HASHO_PAGE_ID;
|
|
|
|
MarkBufferDirty(ovflbuf);
|
|
|
|
/* logically chain overflow page to previous page */
|
|
pageopaque->hasho_nextblkno = BufferGetBlockNumber(ovflbuf);
|
|
_hash_wrtbuf(rel, buf);
|
|
|
|
return ovflbuf;
|
|
}
|
|
|
|
/*
|
|
* _hash_getovflpage()
|
|
*
|
|
* Find an available overflow page and return it. The returned buffer
|
|
* is pinned and write-locked, and has had _hash_pageinit() applied,
|
|
* but it is caller's responsibility to fill the special space.
|
|
*
|
|
* The caller must hold a pin, but no lock, on the metapage buffer.
|
|
* That buffer is left in the same state at exit.
|
|
*/
|
|
static Buffer
|
|
_hash_getovflpage(Relation rel, Buffer metabuf)
|
|
{
|
|
HashMetaPage metap;
|
|
Buffer mapbuf = 0;
|
|
Buffer newbuf;
|
|
BlockNumber blkno;
|
|
uint32 orig_firstfree;
|
|
uint32 splitnum;
|
|
uint32 *freep = NULL;
|
|
uint32 max_ovflpg;
|
|
uint32 bit;
|
|
uint32 first_page;
|
|
uint32 last_bit;
|
|
uint32 last_page;
|
|
uint32 i,
|
|
j;
|
|
|
|
/* Get exclusive lock on the meta page */
|
|
_hash_chgbufaccess(rel, metabuf, HASH_NOLOCK, HASH_WRITE);
|
|
|
|
_hash_checkpage(rel, metabuf, LH_META_PAGE);
|
|
metap = HashPageGetMeta(BufferGetPage(metabuf));
|
|
|
|
/* start search at hashm_firstfree */
|
|
orig_firstfree = metap->hashm_firstfree;
|
|
first_page = orig_firstfree >> BMPG_SHIFT(metap);
|
|
bit = orig_firstfree & BMPG_MASK(metap);
|
|
i = first_page;
|
|
j = bit / BITS_PER_MAP;
|
|
bit &= ~(BITS_PER_MAP - 1);
|
|
|
|
/* outer loop iterates once per bitmap page */
|
|
for (;;)
|
|
{
|
|
BlockNumber mapblkno;
|
|
Page mappage;
|
|
uint32 last_inpage;
|
|
|
|
/* want to end search with the last existing overflow page */
|
|
splitnum = metap->hashm_ovflpoint;
|
|
max_ovflpg = metap->hashm_spares[splitnum] - 1;
|
|
last_page = max_ovflpg >> BMPG_SHIFT(metap);
|
|
last_bit = max_ovflpg & BMPG_MASK(metap);
|
|
|
|
if (i > last_page)
|
|
break;
|
|
|
|
Assert(i < metap->hashm_nmaps);
|
|
mapblkno = metap->hashm_mapp[i];
|
|
|
|
if (i == last_page)
|
|
last_inpage = last_bit;
|
|
else
|
|
last_inpage = BMPGSZ_BIT(metap) - 1;
|
|
|
|
/* Release exclusive lock on metapage while reading bitmap page */
|
|
_hash_chgbufaccess(rel, metabuf, HASH_READ, HASH_NOLOCK);
|
|
|
|
mapbuf = _hash_getbuf(rel, mapblkno, HASH_WRITE, LH_BITMAP_PAGE);
|
|
mappage = BufferGetPage(mapbuf);
|
|
freep = HashPageGetBitmap(mappage);
|
|
|
|
for (; bit <= last_inpage; j++, bit += BITS_PER_MAP)
|
|
{
|
|
if (freep[j] != ALL_SET)
|
|
goto found;
|
|
}
|
|
|
|
/* No free space here, try to advance to next map page */
|
|
_hash_relbuf(rel, mapbuf);
|
|
i++;
|
|
j = 0; /* scan from start of next map page */
|
|
bit = 0;
|
|
|
|
/* Reacquire exclusive lock on the meta page */
|
|
_hash_chgbufaccess(rel, metabuf, HASH_NOLOCK, HASH_WRITE);
|
|
}
|
|
|
|
/*
|
|
* No free pages --- have to extend the relation to add an overflow page.
|
|
* First, check to see if we have to add a new bitmap page too.
|
|
*/
|
|
if (last_bit == (uint32) (BMPGSZ_BIT(metap) - 1))
|
|
{
|
|
/*
|
|
* We create the new bitmap page with all pages marked "in use".
|
|
* Actually two pages in the new bitmap's range will exist
|
|
* immediately: the bitmap page itself, and the following page which
|
|
* is the one we return to the caller. Both of these are correctly
|
|
* marked "in use". Subsequent pages do not exist yet, but it is
|
|
* convenient to pre-mark them as "in use" too.
|
|
*/
|
|
bit = metap->hashm_spares[splitnum];
|
|
_hash_initbitmap(rel, metap, bitno_to_blkno(metap, bit), MAIN_FORKNUM);
|
|
metap->hashm_spares[splitnum]++;
|
|
}
|
|
else
|
|
{
|
|
/*
|
|
* Nothing to do here; since the page will be past the last used page,
|
|
* we know its bitmap bit was preinitialized to "in use".
|
|
*/
|
|
}
|
|
|
|
/* Calculate address of the new overflow page */
|
|
bit = metap->hashm_spares[splitnum];
|
|
blkno = bitno_to_blkno(metap, bit);
|
|
|
|
/*
|
|
* Fetch the page with _hash_getnewbuf to ensure smgr's idea of the
|
|
* relation length stays in sync with ours. XXX It's annoying to do this
|
|
* with metapage write lock held; would be better to use a lock that
|
|
* doesn't block incoming searches.
|
|
*/
|
|
newbuf = _hash_getnewbuf(rel, blkno, MAIN_FORKNUM);
|
|
|
|
metap->hashm_spares[splitnum]++;
|
|
|
|
/*
|
|
* Adjust hashm_firstfree to avoid redundant searches. But don't risk
|
|
* changing it if someone moved it while we were searching bitmap pages.
|
|
*/
|
|
if (metap->hashm_firstfree == orig_firstfree)
|
|
metap->hashm_firstfree = bit + 1;
|
|
|
|
/* Write updated metapage and release lock, but not pin */
|
|
_hash_chgbufaccess(rel, metabuf, HASH_WRITE, HASH_NOLOCK);
|
|
|
|
return newbuf;
|
|
|
|
found:
|
|
/* convert bit to bit number within page */
|
|
bit += _hash_firstfreebit(freep[j]);
|
|
|
|
/* mark page "in use" in the bitmap */
|
|
SETBIT(freep, bit);
|
|
_hash_wrtbuf(rel, mapbuf);
|
|
|
|
/* Reacquire exclusive lock on the meta page */
|
|
_hash_chgbufaccess(rel, metabuf, HASH_NOLOCK, HASH_WRITE);
|
|
|
|
/* convert bit to absolute bit number */
|
|
bit += (i << BMPG_SHIFT(metap));
|
|
|
|
/* Calculate address of the recycled overflow page */
|
|
blkno = bitno_to_blkno(metap, bit);
|
|
|
|
/*
|
|
* Adjust hashm_firstfree to avoid redundant searches. But don't risk
|
|
* changing it if someone moved it while we were searching bitmap pages.
|
|
*/
|
|
if (metap->hashm_firstfree == orig_firstfree)
|
|
{
|
|
metap->hashm_firstfree = bit + 1;
|
|
|
|
/* Write updated metapage and release lock, but not pin */
|
|
_hash_chgbufaccess(rel, metabuf, HASH_WRITE, HASH_NOLOCK);
|
|
}
|
|
else
|
|
{
|
|
/* We didn't change the metapage, so no need to write */
|
|
_hash_chgbufaccess(rel, metabuf, HASH_READ, HASH_NOLOCK);
|
|
}
|
|
|
|
/* Fetch, init, and return the recycled page */
|
|
return _hash_getinitbuf(rel, blkno);
|
|
}
|
|
|
|
/*
|
|
* _hash_firstfreebit()
|
|
*
|
|
* Return the number of the first bit that is not set in the word 'map'.
|
|
*/
|
|
static uint32
|
|
_hash_firstfreebit(uint32 map)
|
|
{
|
|
uint32 i,
|
|
mask;
|
|
|
|
mask = 0x1;
|
|
for (i = 0; i < BITS_PER_MAP; i++)
|
|
{
|
|
if (!(mask & map))
|
|
return i;
|
|
mask <<= 1;
|
|
}
|
|
|
|
elog(ERROR, "firstfreebit found no free bit");
|
|
|
|
return 0; /* keep compiler quiet */
|
|
}
|
|
|
|
/*
|
|
* _hash_freeovflpage() -
|
|
*
|
|
* Remove this overflow page from its bucket's chain, and mark the page as
|
|
* free. On entry, ovflbuf is write-locked; it is released before exiting.
|
|
*
|
|
* Since this function is invoked in VACUUM, we provide an access strategy
|
|
* parameter that controls fetches of the bucket pages.
|
|
*
|
|
* Returns the block number of the page that followed the given page
|
|
* in the bucket, or InvalidBlockNumber if no following page.
|
|
*
|
|
* NB: caller must not hold lock on metapage, nor on either page that's
|
|
* adjacent in the bucket chain. The caller had better hold exclusive lock
|
|
* on the bucket, too.
|
|
*/
|
|
BlockNumber
|
|
_hash_freeovflpage(Relation rel, Buffer ovflbuf,
|
|
BufferAccessStrategy bstrategy)
|
|
{
|
|
HashMetaPage metap;
|
|
Buffer metabuf;
|
|
Buffer mapbuf;
|
|
BlockNumber ovflblkno;
|
|
BlockNumber prevblkno;
|
|
BlockNumber blkno;
|
|
BlockNumber nextblkno;
|
|
HashPageOpaque ovflopaque;
|
|
Page ovflpage;
|
|
Page mappage;
|
|
uint32 *freep;
|
|
uint32 ovflbitno;
|
|
int32 bitmappage,
|
|
bitmapbit;
|
|
Bucket bucket PG_USED_FOR_ASSERTS_ONLY;
|
|
|
|
/* Get information from the doomed page */
|
|
_hash_checkpage(rel, ovflbuf, LH_OVERFLOW_PAGE);
|
|
ovflblkno = BufferGetBlockNumber(ovflbuf);
|
|
ovflpage = BufferGetPage(ovflbuf);
|
|
ovflopaque = (HashPageOpaque) PageGetSpecialPointer(ovflpage);
|
|
nextblkno = ovflopaque->hasho_nextblkno;
|
|
prevblkno = ovflopaque->hasho_prevblkno;
|
|
bucket = ovflopaque->hasho_bucket;
|
|
|
|
/*
|
|
* Zero the page for debugging's sake; then write and release it. (Note:
|
|
* if we failed to zero the page here, we'd have problems with the Assert
|
|
* in _hash_pageinit() when the page is reused.)
|
|
*/
|
|
MemSet(ovflpage, 0, BufferGetPageSize(ovflbuf));
|
|
_hash_wrtbuf(rel, ovflbuf);
|
|
|
|
/*
|
|
* Fix up the bucket chain. this is a doubly-linked list, so we must fix
|
|
* up the bucket chain members behind and ahead of the overflow page being
|
|
* deleted. No concurrency issues since we hold exclusive lock on the
|
|
* entire bucket.
|
|
*/
|
|
if (BlockNumberIsValid(prevblkno))
|
|
{
|
|
Buffer prevbuf = _hash_getbuf_with_strategy(rel,
|
|
prevblkno,
|
|
HASH_WRITE,
|
|
LH_BUCKET_PAGE | LH_OVERFLOW_PAGE,
|
|
bstrategy);
|
|
Page prevpage = BufferGetPage(prevbuf);
|
|
HashPageOpaque prevopaque = (HashPageOpaque) PageGetSpecialPointer(prevpage);
|
|
|
|
Assert(prevopaque->hasho_bucket == bucket);
|
|
prevopaque->hasho_nextblkno = nextblkno;
|
|
_hash_wrtbuf(rel, prevbuf);
|
|
}
|
|
if (BlockNumberIsValid(nextblkno))
|
|
{
|
|
Buffer nextbuf = _hash_getbuf_with_strategy(rel,
|
|
nextblkno,
|
|
HASH_WRITE,
|
|
LH_OVERFLOW_PAGE,
|
|
bstrategy);
|
|
Page nextpage = BufferGetPage(nextbuf);
|
|
HashPageOpaque nextopaque = (HashPageOpaque) PageGetSpecialPointer(nextpage);
|
|
|
|
Assert(nextopaque->hasho_bucket == bucket);
|
|
nextopaque->hasho_prevblkno = prevblkno;
|
|
_hash_wrtbuf(rel, nextbuf);
|
|
}
|
|
|
|
/* Note: bstrategy is intentionally not used for metapage and bitmap */
|
|
|
|
/* Read the metapage so we can determine which bitmap page to use */
|
|
metabuf = _hash_getbuf(rel, HASH_METAPAGE, HASH_READ, LH_META_PAGE);
|
|
metap = HashPageGetMeta(BufferGetPage(metabuf));
|
|
|
|
/* Identify which bit to set */
|
|
ovflbitno = blkno_to_bitno(metap, ovflblkno);
|
|
|
|
bitmappage = ovflbitno >> BMPG_SHIFT(metap);
|
|
bitmapbit = ovflbitno & BMPG_MASK(metap);
|
|
|
|
if (bitmappage >= metap->hashm_nmaps)
|
|
elog(ERROR, "invalid overflow bit number %u", ovflbitno);
|
|
blkno = metap->hashm_mapp[bitmappage];
|
|
|
|
/* Release metapage lock while we access the bitmap page */
|
|
_hash_chgbufaccess(rel, metabuf, HASH_READ, HASH_NOLOCK);
|
|
|
|
/* Clear the bitmap bit to indicate that this overflow page is free */
|
|
mapbuf = _hash_getbuf(rel, blkno, HASH_WRITE, LH_BITMAP_PAGE);
|
|
mappage = BufferGetPage(mapbuf);
|
|
freep = HashPageGetBitmap(mappage);
|
|
Assert(ISSET(freep, bitmapbit));
|
|
CLRBIT(freep, bitmapbit);
|
|
_hash_wrtbuf(rel, mapbuf);
|
|
|
|
/* Get write-lock on metapage to update firstfree */
|
|
_hash_chgbufaccess(rel, metabuf, HASH_NOLOCK, HASH_WRITE);
|
|
|
|
/* if this is now the first free page, update hashm_firstfree */
|
|
if (ovflbitno < metap->hashm_firstfree)
|
|
{
|
|
metap->hashm_firstfree = ovflbitno;
|
|
_hash_wrtbuf(rel, metabuf);
|
|
}
|
|
else
|
|
{
|
|
/* no need to change metapage */
|
|
_hash_relbuf(rel, metabuf);
|
|
}
|
|
|
|
return nextblkno;
|
|
}
|
|
|
|
|
|
/*
|
|
* _hash_initbitmap()
|
|
*
|
|
* Initialize a new bitmap page. The metapage has a write-lock upon
|
|
* entering the function, and must be written by caller after return.
|
|
*
|
|
* 'blkno' is the block number of the new bitmap page.
|
|
*
|
|
* All bits in the new bitmap page are set to "1", indicating "in use".
|
|
*/
|
|
void
|
|
_hash_initbitmap(Relation rel, HashMetaPage metap, BlockNumber blkno,
|
|
ForkNumber forkNum)
|
|
{
|
|
Buffer buf;
|
|
Page pg;
|
|
HashPageOpaque op;
|
|
uint32 *freep;
|
|
|
|
/*
|
|
* It is okay to write-lock the new bitmap page while holding metapage
|
|
* write lock, because no one else could be contending for the new page.
|
|
* Also, the metapage lock makes it safe to extend the index using
|
|
* _hash_getnewbuf.
|
|
*
|
|
* There is some loss of concurrency in possibly doing I/O for the new
|
|
* page while holding the metapage lock, but this path is taken so seldom
|
|
* that it's not worth worrying about.
|
|
*/
|
|
buf = _hash_getnewbuf(rel, blkno, forkNum);
|
|
pg = BufferGetPage(buf);
|
|
|
|
/* initialize the page's special space */
|
|
op = (HashPageOpaque) PageGetSpecialPointer(pg);
|
|
op->hasho_prevblkno = InvalidBlockNumber;
|
|
op->hasho_nextblkno = InvalidBlockNumber;
|
|
op->hasho_bucket = -1;
|
|
op->hasho_flag = LH_BITMAP_PAGE;
|
|
op->hasho_page_id = HASHO_PAGE_ID;
|
|
|
|
/* set all of the bits to 1 */
|
|
freep = HashPageGetBitmap(pg);
|
|
MemSet(freep, 0xFF, BMPGSZ_BYTE(metap));
|
|
|
|
/* write out the new bitmap page (releasing write lock and pin) */
|
|
_hash_wrtbuf(rel, buf);
|
|
|
|
/* add the new bitmap page to the metapage's list of bitmaps */
|
|
/* metapage already has a write lock */
|
|
if (metap->hashm_nmaps >= HASH_MAX_BITMAPS)
|
|
ereport(ERROR,
|
|
(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
|
|
errmsg("out of overflow pages in hash index \"%s\"",
|
|
RelationGetRelationName(rel))));
|
|
|
|
metap->hashm_mapp[metap->hashm_nmaps] = blkno;
|
|
|
|
metap->hashm_nmaps++;
|
|
}
|
|
|
|
|
|
/*
|
|
* _hash_squeezebucket(rel, bucket)
|
|
*
|
|
* Try to squeeze the tuples onto pages occurring earlier in the
|
|
* bucket chain in an attempt to free overflow pages. When we start
|
|
* the "squeezing", the page from which we start taking tuples (the
|
|
* "read" page) is the last bucket in the bucket chain and the page
|
|
* onto which we start squeezing tuples (the "write" page) is the
|
|
* first page in the bucket chain. The read page works backward and
|
|
* the write page works forward; the procedure terminates when the
|
|
* read page and write page are the same page.
|
|
*
|
|
* At completion of this procedure, it is guaranteed that all pages in
|
|
* the bucket are nonempty, unless the bucket is totally empty (in
|
|
* which case all overflow pages will be freed). The original implementation
|
|
* required that to be true on entry as well, but it's a lot easier for
|
|
* callers to leave empty overflow pages and let this guy clean it up.
|
|
*
|
|
* Caller must hold exclusive lock on the target bucket. This allows
|
|
* us to safely lock multiple pages in the bucket.
|
|
*
|
|
* Since this function is invoked in VACUUM, we provide an access strategy
|
|
* parameter that controls fetches of the bucket pages.
|
|
*/
|
|
void
|
|
_hash_squeezebucket(Relation rel,
|
|
Bucket bucket,
|
|
BlockNumber bucket_blkno,
|
|
BufferAccessStrategy bstrategy)
|
|
{
|
|
BlockNumber wblkno;
|
|
BlockNumber rblkno;
|
|
Buffer wbuf;
|
|
Buffer rbuf;
|
|
Page wpage;
|
|
Page rpage;
|
|
HashPageOpaque wopaque;
|
|
HashPageOpaque ropaque;
|
|
bool wbuf_dirty;
|
|
|
|
/*
|
|
* start squeezing into the base bucket page.
|
|
*/
|
|
wblkno = bucket_blkno;
|
|
wbuf = _hash_getbuf_with_strategy(rel,
|
|
wblkno,
|
|
HASH_WRITE,
|
|
LH_BUCKET_PAGE,
|
|
bstrategy);
|
|
wpage = BufferGetPage(wbuf);
|
|
wopaque = (HashPageOpaque) PageGetSpecialPointer(wpage);
|
|
|
|
/*
|
|
* if there aren't any overflow pages, there's nothing to squeeze.
|
|
*/
|
|
if (!BlockNumberIsValid(wopaque->hasho_nextblkno))
|
|
{
|
|
_hash_relbuf(rel, wbuf);
|
|
return;
|
|
}
|
|
|
|
/*
|
|
* Find the last page in the bucket chain by starting at the base bucket
|
|
* page and working forward. Note: we assume that a hash bucket chain is
|
|
* usually smaller than the buffer ring being used by VACUUM, else using
|
|
* the access strategy here would be counterproductive.
|
|
*/
|
|
rbuf = InvalidBuffer;
|
|
ropaque = wopaque;
|
|
do
|
|
{
|
|
rblkno = ropaque->hasho_nextblkno;
|
|
if (rbuf != InvalidBuffer)
|
|
_hash_relbuf(rel, rbuf);
|
|
rbuf = _hash_getbuf_with_strategy(rel,
|
|
rblkno,
|
|
HASH_WRITE,
|
|
LH_OVERFLOW_PAGE,
|
|
bstrategy);
|
|
rpage = BufferGetPage(rbuf);
|
|
ropaque = (HashPageOpaque) PageGetSpecialPointer(rpage);
|
|
Assert(ropaque->hasho_bucket == bucket);
|
|
} while (BlockNumberIsValid(ropaque->hasho_nextblkno));
|
|
|
|
/*
|
|
* squeeze the tuples.
|
|
*/
|
|
wbuf_dirty = false;
|
|
for (;;)
|
|
{
|
|
OffsetNumber roffnum;
|
|
OffsetNumber maxroffnum;
|
|
OffsetNumber deletable[MaxOffsetNumber];
|
|
int ndeletable = 0;
|
|
|
|
/* Scan each tuple in "read" page */
|
|
maxroffnum = PageGetMaxOffsetNumber(rpage);
|
|
for (roffnum = FirstOffsetNumber;
|
|
roffnum <= maxroffnum;
|
|
roffnum = OffsetNumberNext(roffnum))
|
|
{
|
|
IndexTuple itup;
|
|
Size itemsz;
|
|
|
|
itup = (IndexTuple) PageGetItem(rpage,
|
|
PageGetItemId(rpage, roffnum));
|
|
itemsz = IndexTupleDSize(*itup);
|
|
itemsz = MAXALIGN(itemsz);
|
|
|
|
/*
|
|
* Walk up the bucket chain, looking for a page big enough for
|
|
* this item. Exit if we reach the read page.
|
|
*/
|
|
while (PageGetFreeSpace(wpage) < itemsz)
|
|
{
|
|
Assert(!PageIsEmpty(wpage));
|
|
|
|
wblkno = wopaque->hasho_nextblkno;
|
|
Assert(BlockNumberIsValid(wblkno));
|
|
|
|
if (wbuf_dirty)
|
|
_hash_wrtbuf(rel, wbuf);
|
|
else
|
|
_hash_relbuf(rel, wbuf);
|
|
|
|
/* nothing more to do if we reached the read page */
|
|
if (rblkno == wblkno)
|
|
{
|
|
if (ndeletable > 0)
|
|
{
|
|
/* Delete tuples we already moved off read page */
|
|
PageIndexMultiDelete(rpage, deletable, ndeletable);
|
|
_hash_wrtbuf(rel, rbuf);
|
|
}
|
|
else
|
|
_hash_relbuf(rel, rbuf);
|
|
return;
|
|
}
|
|
|
|
wbuf = _hash_getbuf_with_strategy(rel,
|
|
wblkno,
|
|
HASH_WRITE,
|
|
LH_OVERFLOW_PAGE,
|
|
bstrategy);
|
|
wpage = BufferGetPage(wbuf);
|
|
wopaque = (HashPageOpaque) PageGetSpecialPointer(wpage);
|
|
Assert(wopaque->hasho_bucket == bucket);
|
|
wbuf_dirty = false;
|
|
}
|
|
|
|
/*
|
|
* we have found room so insert on the "write" page, being careful
|
|
* to preserve hashkey ordering. (If we insert many tuples into
|
|
* the same "write" page it would be worth qsort'ing instead of
|
|
* doing repeated _hash_pgaddtup.)
|
|
*/
|
|
(void) _hash_pgaddtup(rel, wbuf, itemsz, itup);
|
|
wbuf_dirty = true;
|
|
|
|
/* remember tuple for deletion from "read" page */
|
|
deletable[ndeletable++] = roffnum;
|
|
}
|
|
|
|
/*
|
|
* If we reach here, there are no live tuples on the "read" page ---
|
|
* it was empty when we got to it, or we moved them all. So we can
|
|
* just free the page without bothering with deleting tuples
|
|
* individually. Then advance to the previous "read" page.
|
|
*
|
|
* Tricky point here: if our read and write pages are adjacent in the
|
|
* bucket chain, our write lock on wbuf will conflict with
|
|
* _hash_freeovflpage's attempt to update the sibling links of the
|
|
* removed page. However, in that case we are done anyway, so we can
|
|
* simply drop the write lock before calling _hash_freeovflpage.
|
|
*/
|
|
rblkno = ropaque->hasho_prevblkno;
|
|
Assert(BlockNumberIsValid(rblkno));
|
|
|
|
/* are we freeing the page adjacent to wbuf? */
|
|
if (rblkno == wblkno)
|
|
{
|
|
/* yes, so release wbuf lock first */
|
|
if (wbuf_dirty)
|
|
_hash_wrtbuf(rel, wbuf);
|
|
else
|
|
_hash_relbuf(rel, wbuf);
|
|
/* free this overflow page (releases rbuf) */
|
|
_hash_freeovflpage(rel, rbuf, bstrategy);
|
|
/* done */
|
|
return;
|
|
}
|
|
|
|
/* free this overflow page, then get the previous one */
|
|
_hash_freeovflpage(rel, rbuf, bstrategy);
|
|
|
|
rbuf = _hash_getbuf_with_strategy(rel,
|
|
rblkno,
|
|
HASH_WRITE,
|
|
LH_OVERFLOW_PAGE,
|
|
bstrategy);
|
|
rpage = BufferGetPage(rbuf);
|
|
ropaque = (HashPageOpaque) PageGetSpecialPointer(rpage);
|
|
Assert(ropaque->hasho_bucket == bucket);
|
|
}
|
|
|
|
/* NOTREACHED */
|
|
}
|