/*
* _hash_splitbucket -- split 'obucket' into 'obucket' and 'nbucket'
*
* We are splitting a bucket that consists of a base bucket page and zero
* or more overflow (bucket chain) pages. We must relocate tuples that
* belong in the new bucket, and compress out any free space in the old
* bucket.
*
* The caller must hold exclusive locks on both buckets to ensure that
* no one else is trying to access them (see README).
*
* The caller must hold a pin, but no lock, on the metapage buffer.
* The buffer is returned in the same state. (The metapage is only
* touched if it becomes necessary to add or remove overflow pages.)
*/
static void
_hash_splitbucket(Relation rel,
Buffer metabuf,
Bucket obucket,
Bucket nbucket,
BlockNumber start_oblkno,
BlockNumber start_nblkno,
uint32 maxbucket,
uint32 highmask,
uint32 lowmask)
{
Bucket bucket;
Buffer obuf;
Buffer nbuf;
BlockNumber oblkno;
BlockNumber nblkno;
bool null;
Datum datum;
HashPageOpaque oopaque;
HashPageOpaque nopaque;
IndexTuple itup;
Size itemsz;
OffsetNumber ooffnum;
OffsetNumber noffnum;
OffsetNumber omaxoffnum;
Page opage;
Page npage;
TupleDesc itupdesc = RelationGetDescr(rel);
MIRROREDLOCK_BUFMGR_MUST_ALREADY_BE_HELD;
/*
* It should be okay to simultaneously write-lock pages from each bucket,
* since no one else can be trying to acquire buffer lock on pages of
* either bucket.
*/
oblkno = start_oblkno;
obuf = _hash_getbuf(rel, oblkno, HASH_WRITE);
_hash_checkpage(rel, obuf, LH_BUCKET_PAGE);
opage = BufferGetPage(obuf);
oopaque = (HashPageOpaque) PageGetSpecialPointer(opage);
nblkno = start_nblkno;
nbuf = _hash_getbuf(rel, nblkno, HASH_WRITE);
npage = BufferGetPage(nbuf);
/* initialize the new bucket's primary page */
_hash_pageinit(npage, BufferGetPageSize(nbuf));
nopaque = (HashPageOpaque) PageGetSpecialPointer(npage);
nopaque->hasho_prevblkno = InvalidBlockNumber;
nopaque->hasho_nextblkno = InvalidBlockNumber;
nopaque->hasho_bucket = nbucket;
nopaque->hasho_flag = LH_BUCKET_PAGE;
nopaque->hasho_filler = HASHO_FILL;
/*
* Partition the tuples in the old bucket between the old bucket and the
* new bucket, advancing along the old bucket's overflow bucket chain and
* adding overflow pages to the new bucket 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 an(other) overflow page */
oblkno = oopaque->hasho_nextblkno;
if (!BlockNumberIsValid(oblkno))
break;
/*
* we ran out of tuples on this particular page, but we have more
* overflow pages; advance to next page.
*/
_hash_wrtbuf(rel, obuf);
obuf = _hash_getbuf(rel, oblkno, HASH_WRITE);
_hash_checkpage(rel, obuf, LH_OVERFLOW_PAGE);
opage = BufferGetPage(obuf);
oopaque = (HashPageOpaque) PageGetSpecialPointer(opage);
ooffnum = FirstOffsetNumber;
omaxoffnum = PageGetMaxOffsetNumber(opage);
continue;
}
/*
* Re-hash the tuple to determine which bucket it now belongs in.
*
* It is annoying to call the hash function while holding locks, but
* releasing and relocking the page for each tuple is unappealing too.
*/
itup = (IndexTuple) PageGetItem(opage, PageGetItemId(opage, ooffnum));
datum = index_getattr(itup, 1, itupdesc, &null);
Assert(!null);
bucket = _hash_hashkey2bucket(_hash_datum2hashkey(rel, datum),
maxbucket, highmask, lowmask);
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(*itup);
itemsz = MAXALIGN(itemsz);
if (PageGetFreeSpace(npage) < itemsz)
{
/* write out nbuf and drop lock, but keep pin */
_hash_chgbufaccess(rel, nbuf, HASH_WRITE, HASH_NOLOCK);
/* chain to a new overflow page */
nbuf = _hash_addovflpage(rel, metabuf, nbuf);
_hash_checkpage(rel, nbuf, LH_OVERFLOW_PAGE);
npage = BufferGetPage(nbuf);
/* we don't need nopaque within the loop */
}
noffnum = OffsetNumberNext(PageGetMaxOffsetNumber(npage));
if (PageAddItem(npage, (Item) itup, itemsz, noffnum, LP_USED)
== InvalidOffsetNumber)
elog(ERROR, "failed to add index item to \"%s\"",
RelationGetRelationName(rel));
/*
* 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);
omaxoffnum = OffsetNumberPrev(omaxoffnum);
}
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'.
*/
Assert(bucket == obucket);
ooffnum = OffsetNumberNext(ooffnum);
}
}
/*
* We're at the end of the old bucket chain, so we're done partitioning
* the tuples. Before quitting, call _hash_squeezebucket to ensure the
* tuples remaining in the old bucket (including the overflow pages) are
* packed as tightly as possible. The new bucket is already tight.
*/
_hash_wrtbuf(rel, obuf);
_hash_wrtbuf(rel, nbuf);
_hash_squeezebucket(rel, obucket, start_oblkno);
}
/*
* _hash_init_metabuffer() -- Initialize the metadata page of a hash index.
*/
void
_hash_init_metabuffer(Buffer buf, double num_tuples, RegProcedure procid,
uint16 ffactor, bool initpage)
{
HashMetaPage metap;
HashPageOpaque pageopaque;
Page page;
double dnumbuckets;
uint32 num_buckets;
uint32 spare_index;
uint32 i;
/*
* Choose the number of initial bucket pages to match the fill factor
* given the estimated number of tuples. We round up the result to the
* total number of buckets which has to be allocated before using its
* _hashm_spare element. However always force at least 2 bucket pages. The
* upper limit is determined by considerations explained in
* _hash_expandtable().
*/
dnumbuckets = num_tuples / ffactor;
if (dnumbuckets <= 2.0)
num_buckets = 2;
else if (dnumbuckets >= (double) 0x40000000)
num_buckets = 0x40000000;
else
num_buckets = _hash_get_totalbuckets(_hash_spareindex(dnumbuckets));
spare_index = _hash_spareindex(num_buckets);
Assert(spare_index < HASH_MAX_SPLITPOINTS);
page = BufferGetPage(buf);
if (initpage)
_hash_pageinit(page, BufferGetPageSize(buf));
pageopaque = (HashPageOpaque) PageGetSpecialPointer(page);
pageopaque->hasho_prevblkno = InvalidBlockNumber;
pageopaque->hasho_nextblkno = InvalidBlockNumber;
pageopaque->hasho_bucket = -1;
pageopaque->hasho_flag = LH_META_PAGE;
pageopaque->hasho_page_id = HASHO_PAGE_ID;
metap = HashPageGetMeta(page);
metap->hashm_magic = HASH_MAGIC;
metap->hashm_version = HASH_VERSION;
metap->hashm_ntuples = 0;
metap->hashm_nmaps = 0;
metap->hashm_ffactor = ffactor;
metap->hashm_bsize = HashGetMaxBitmapSize(page);
/* find largest bitmap array size that will fit in page size */
for (i = _hash_log2(metap->hashm_bsize); i > 0; --i)
{
if ((1 << i) <= metap->hashm_bsize)
break;
}
Assert(i > 0);
metap->hashm_bmsize = 1 << i;
metap->hashm_bmshift = i + BYTE_TO_BIT;
Assert((1 << BMPG_SHIFT(metap)) == (BMPG_MASK(metap) + 1));
/*
* Label the index with its primary hash support function's OID. This is
* pretty useless for normal operation (in fact, hashm_procid is not used
* anywhere), but it might be handy for forensic purposes so we keep it.
*/
metap->hashm_procid = procid;
/*
* We initialize the index with N buckets, 0 .. N-1, occupying physical
* blocks 1 to N. The first freespace bitmap page is in block N+1.
*/
metap->hashm_maxbucket = num_buckets - 1;
/*
* Set highmask as next immediate ((2 ^ x) - 1), which should be
* sufficient to cover num_buckets.
*/
metap->hashm_highmask = (1 << (_hash_log2(num_buckets + 1))) - 1;
metap->hashm_lowmask = (metap->hashm_highmask >> 1);
MemSet(metap->hashm_spares, 0, sizeof(metap->hashm_spares));
MemSet(metap->hashm_mapp, 0, sizeof(metap->hashm_mapp));
/* Set up mapping for one spare page after the initial splitpoints */
metap->hashm_spares[spare_index] = 1;
metap->hashm_ovflpoint = spare_index;
metap->hashm_firstfree = 0;
/*
* Set pd_lower just past the end of the metadata. This is to log full
* page image of metapage in xloginsert.c.
*/
((PageHeader) page)->pd_lower =
((char *) metap + sizeof(HashMetaPageData)) - (char *) page;
}
/*
* _hash_metapinit() -- Initialize the metadata page of a hash index,
* the two buckets that we begin with and the initial
* bitmap page.
*
* We are fairly cavalier about locking here, since we know that no one else
* could be accessing this index. In particular the rule about not holding
* multiple buffer locks is ignored.
*/
void
_hash_metapinit(Relation rel)
{
MIRROREDLOCK_BUFMGR_DECLARE;
HashMetaPage metap;
HashPageOpaque pageopaque;
Buffer metabuf;
Buffer buf;
Page pg;
int32 data_width;
int32 item_width;
int32 ffactor;
uint16 i;
/* safety check */
if (RelationGetNumberOfBlocks(rel) != 0)
elog(ERROR, "cannot initialize non-empty hash index \"%s\"",
RelationGetRelationName(rel));
/*
* Determine the target fill factor (in tuples per bucket) for this index.
* The idea is to make the fill factor correspond to pages about as full
* as the user-settable fillfactor parameter says. We can compute it
* exactly if the index datatype is fixed-width, but for var-width there's
* some guessing involved.
*/
data_width = get_typavgwidth(RelationGetDescr(rel)->attrs[0]->atttypid,
RelationGetDescr(rel)->attrs[0]->atttypmod);
item_width = MAXALIGN(sizeof(IndexTupleData)) + MAXALIGN(data_width) +
sizeof(ItemIdData); /* include the line pointer */
ffactor = RelationGetTargetPageUsage(rel, HASH_DEFAULT_FILLFACTOR) / item_width;
/* keep to a sane range */
if (ffactor < 10)
ffactor = 10;
/*
* We initialize the metapage, the first two bucket pages, and the
* first bitmap page in sequence, using _hash_getnewbuf to cause
* smgrextend() calls to occur. This ensures that the smgr level
* has the right idea of the physical index length.
*/
// -------- MirroredLock ----------
MIRROREDLOCK_BUFMGR_LOCK;
metabuf = _hash_getnewbuf(rel, HASH_METAPAGE, HASH_WRITE);
pg = BufferGetPage(metabuf);
_hash_pageinit(pg, BufferGetPageSize(metabuf));
pageopaque = (HashPageOpaque) PageGetSpecialPointer(pg);
pageopaque->hasho_prevblkno = InvalidBlockNumber;
pageopaque->hasho_nextblkno = InvalidBlockNumber;
pageopaque->hasho_bucket = -1;
pageopaque->hasho_flag = LH_META_PAGE;
pageopaque->hasho_filler = HASHO_FILL;
metap = (HashMetaPage) pg;
metap->hashm_magic = HASH_MAGIC;
metap->hashm_version = HASH_VERSION;
metap->hashm_ntuples = 0;
metap->hashm_nmaps = 0;
metap->hashm_ffactor = ffactor;
metap->hashm_bsize = BufferGetPageSize(metabuf);
/* find largest bitmap array size that will fit in page size */
for (i = _hash_log2(metap->hashm_bsize); i > 0; --i)
{
if ((1 << i) <= (metap->hashm_bsize -
(MAXALIGN(sizeof(PageHeaderData)) +
MAXALIGN(sizeof(HashPageOpaqueData)))))
break;
}
Assert(i > 0);
metap->hashm_bmsize = 1 << i;
metap->hashm_bmshift = i + BYTE_TO_BIT;
Assert((1 << BMPG_SHIFT(metap)) == (BMPG_MASK(metap) + 1));
metap->hashm_procid = index_getprocid(rel, 1, HASHPROC);
/*
* We initialize the index with two buckets, 0 and 1, occupying physical
* blocks 1 and 2. The first freespace bitmap page is in block 3.
*/
metap->hashm_maxbucket = metap->hashm_lowmask = 1; /* nbuckets - 1 */
metap->hashm_highmask = 3; /* (nbuckets << 1) - 1 */
MemSet(metap->hashm_spares, 0, sizeof(metap->hashm_spares));
MemSet(metap->hashm_mapp, 0, sizeof(metap->hashm_mapp));
metap->hashm_spares[1] = 1; /* the first bitmap page is only spare */
metap->hashm_ovflpoint = 1;
metap->hashm_firstfree = 0;
/*
* Initialize the first two buckets
*/
for (i = 0; i <= 1; i++)
{
buf = _hash_getnewbuf(rel, BUCKET_TO_BLKNO(metap, i), HASH_WRITE);
pg = BufferGetPage(buf);
_hash_pageinit(pg, BufferGetPageSize(buf));
pageopaque = (HashPageOpaque) PageGetSpecialPointer(pg);
pageopaque->hasho_prevblkno = InvalidBlockNumber;
pageopaque->hasho_nextblkno = InvalidBlockNumber;
pageopaque->hasho_bucket = i;
pageopaque->hasho_flag = LH_BUCKET_PAGE;
pageopaque->hasho_filler = HASHO_FILL;
_hash_wrtbuf(rel, buf);
}
/*
* Initialize first bitmap page
*/
_hash_initbitmap(rel, metap, 3);
/* all done */
_hash_wrtbuf(rel, metabuf);
MIRROREDLOCK_BUFMGR_UNLOCK;
// -------- MirroredLock ----------
}
