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Postgres FD Implementation
Commit 21a3cf41 authored by Robert Haas's avatar Robert Haas
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hash: Refactor and clean up bucket split code. 

As with commit 30df93f6 and commit
b0f18cb7, the goal here is to move all
of the related page modifications to a single section of code, in
preparation for adding write-ahead logging.

Amit Kapila, with slight changes by me.  The larger patch series of
which this is a part has been reviewed and tested by Álvaro Herrera,
Ashutosh Sharma, Mark Kirkwood, Jeff Janes, and Jesper Pedersen.
parent 123ccbe5
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Showing with 67 additions and 93 deletions
src/backend/access/hash/hashpage.c
View file @ 21a3cf41
......@@ -40,12 +40,9 @@ static void _hash_splitbucket(Relation rel, Buffer metabuf,
Bucket obucket, Bucket nbucket,
Buffer obuf,
Buffer nbuf,
HTAB *htab,
uint32 maxbucket,
uint32 highmask, uint32 lowmask);
static void _hash_splitbucket_guts(Relation rel, Buffer metabuf,
Bucket obucket, Bucket nbucket, Buffer obuf,
Buffer nbuf, HTAB *htab, uint32 maxbucket,
uint32 highmask, uint32 lowmask);
/*
......@@ -497,7 +494,9 @@ _hash_expandtable(Relation rel, Buffer metabuf)
Buffer buf_nblkno;
Buffer buf_oblkno;
Page opage;
Page npage;
HashPageOpaque oopaque;
HashPageOpaque nopaque;
uint32 maxbucket;
uint32 highmask;
uint32 lowmask;
......@@ -685,18 +684,18 @@ restart_expand:
goto fail;
}
/*
* Okay to proceed with split. Update the metapage bucket mapping info.
*
* Since we are scribbling on the metapage data right in the shared
* buffer, any failure in this next little bit leaves us with a big
* Since we are scribbling on the pages in the shared buffers, establish a
* critical section. Any failure in this next code leaves us with a big
* problem: the metapage is effectively corrupt but could get written back
* to disk. We don't really expect any failure, but just to be sure,
* establish a critical section.
*/
START_CRIT_SECTION();
/*
* Okay to proceed with split. Update the metapage bucket mapping info.
*/
metap->hashm_maxbucket = new_bucket;
if (new_bucket > metap->hashm_highmask)
......@@ -718,8 +717,7 @@ restart_expand:
metap->hashm_ovflpoint = spare_ndx;
}
/* Done mucking with metapage */
END_CRIT_SECTION();
MarkBufferDirty(metabuf);
/*
* Copy bucket mapping info now; this saves re-accessing the meta page
......@@ -732,16 +730,51 @@ restart_expand:
highmask = metap->hashm_highmask;
lowmask = metap->hashm_lowmask;
/* Write out the metapage and drop lock, but keep pin */
MarkBufferDirty(metabuf);
opage = BufferGetPage(buf_oblkno);
oopaque = (HashPageOpaque) PageGetSpecialPointer(opage);
/*
* Mark the old bucket to indicate that split is in progress. (At
* operation end, we will clear the split-in-progress flag.) Also,
* for a primary bucket page, hasho_prevblkno stores the number of
* buckets that existed as of the last split, so we must update that
* value here.
*/
oopaque->hasho_flag |= LH_BUCKET_BEING_SPLIT;
oopaque->hasho_prevblkno = maxbucket;
MarkBufferDirty(buf_oblkno);
npage = BufferGetPage(buf_nblkno);
/*
* initialize the new bucket's primary page and mark it to indicate that
* split is in progress.
*/
nopaque = (HashPageOpaque) PageGetSpecialPointer(npage);
nopaque->hasho_prevblkno = maxbucket;
nopaque->hasho_nextblkno = InvalidBlockNumber;
nopaque->hasho_bucket = new_bucket;
nopaque->hasho_flag = LH_BUCKET_PAGE | LH_BUCKET_BEING_POPULATED;
nopaque->hasho_page_id = HASHO_PAGE_ID;
MarkBufferDirty(buf_nblkno);
END_CRIT_SECTION();
/* drop lock, but keep pin */
LockBuffer(metabuf, BUFFER_LOCK_UNLOCK);
/* Relocate records to the new bucket */
_hash_splitbucket(rel, metabuf,
old_bucket, new_bucket,
buf_oblkno, buf_nblkno,
buf_oblkno, buf_nblkno, NULL,
maxbucket, highmask, lowmask);
/* all done, now release the locks and pins on primary buckets. */
_hash_relbuf(rel, buf_oblkno);
_hash_relbuf(rel, buf_nblkno);
return;
/* Here if decide not to split or fail to acquire old bucket lock */
......@@ -803,10 +836,16 @@ _hash_alloc_buckets(Relation rel, BlockNumber firstblock, uint32 nblocks)
/*
* _hash_splitbucket -- split 'obucket' into 'obucket' and 'nbucket'
*
* This routine is used to partition the tuples between old and new bucket and
* is used to finish the incomplete split operations. To finish the previously
* interrupted split operation, the caller needs to fill htab. If htab is set,
* then we skip the movement of tuples that exists in htab, otherwise NULL
* value of htab indicates movement of all the tuples that belong to the new
* bucket.
*
* 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.
* belong in the new bucket.
*
* The caller must hold cleanup locks on both buckets to ensure that
* no one else is trying to access them (see README).
......@@ -832,72 +871,10 @@ _hash_splitbucket(Relation rel,
Bucket nbucket,
Buffer obuf,
Buffer nbuf,
HTAB *htab,
uint32 maxbucket,
uint32 highmask,
uint32 lowmask)
{
Page opage;
Page npage;
HashPageOpaque oopaque;
HashPageOpaque nopaque;
opage = BufferGetPage(obuf);
oopaque = (HashPageOpaque) PageGetSpecialPointer(opage);
/*
* Mark the old bucket to indicate that split is in progress. (At
* operation end, we will clear the split-in-progress flag.) Also,
* for a primary bucket page, hasho_prevblkno stores the number of
* buckets that existed as of the last split, so we must update that
* value here.
*/
oopaque->hasho_flag |= LH_BUCKET_BEING_SPLIT;
oopaque->hasho_prevblkno = maxbucket;
npage = BufferGetPage(nbuf);
/*
* initialize the new bucket's primary page and mark it to indicate that
* split is in progress.
*/
nopaque = (HashPageOpaque) PageGetSpecialPointer(npage);
nopaque->hasho_prevblkno = maxbucket;
nopaque->hasho_nextblkno = InvalidBlockNumber;
nopaque->hasho_bucket = nbucket;
nopaque->hasho_flag = LH_BUCKET_PAGE | LH_BUCKET_BEING_POPULATED;
nopaque->hasho_page_id = HASHO_PAGE_ID;
_hash_splitbucket_guts(rel, metabuf, obucket,
nbucket, obuf, nbuf, NULL,
maxbucket, highmask, lowmask);
/* all done, now release the locks and pins on primary buckets. */
_hash_relbuf(rel, obuf);
_hash_relbuf(rel, nbuf);
}
/*
* _hash_splitbucket_guts -- Helper function to perform the split operation
*
* This routine is used to partition the tuples between old and new bucket and
* to finish incomplete split operations. To finish the previously
* interrupted split operation, caller needs to fill htab. If htab is set, then
* we skip the movement of tuples that exists in htab, otherwise NULL value of
* htab indicates movement of all the tuples that belong to new bucket.
*
* Caller needs to lock and unlock the old and new primary buckets.
*/
static void
_hash_splitbucket_guts(Relation rel,
Buffer metabuf,
Bucket obucket,
Bucket nbucket,
Buffer obuf,
Buffer nbuf,
HTAB *htab,
uint32 maxbucket,
uint32 highmask,
uint32 lowmask)
{
Buffer bucket_obuf;
Buffer bucket_nbuf;
......@@ -987,6 +964,7 @@ _hash_splitbucket_guts(Relation rel,
{
/* write out nbuf and drop lock, but keep pin */
MarkBufferDirty(nbuf);
/* drop lock, but keep pin */
LockBuffer(nbuf, BUFFER_LOCK_UNLOCK);
/* chain to a new overflow page */
nbuf = _hash_addovflpage(rel, metabuf, nbuf, (nbuf == bucket_nbuf) ? true : false);
......@@ -1025,7 +1003,14 @@ _hash_splitbucket_guts(Relation rel,
/* Exit loop if no more overflow pages in old bucket */
if (!BlockNumberIsValid(oblkno))
{
MarkBufferDirty(nbuf);
if (nbuf == bucket_nbuf)
LockBuffer(nbuf, BUFFER_LOCK_UNLOCK);
else
_hash_relbuf(rel, nbuf);
break;
}
/* Else, advance to next old page */
obuf = _hash_getbuf(rel, oblkno, HASH_READ, LH_OVERFLOW_PAGE);
......@@ -1041,17 +1026,6 @@ _hash_splitbucket_guts(Relation rel,
* To avoid deadlocks due to locking order of buckets, first lock the old
* bucket and then the new bucket.
*/
if (nbuf == bucket_nbuf)
{
MarkBufferDirty(bucket_nbuf);
LockBuffer(bucket_nbuf, BUFFER_LOCK_UNLOCK);
}
else
{
MarkBufferDirty(nbuf);
_hash_relbuf(rel, nbuf);
}
LockBuffer(bucket_obuf, BUFFER_LOCK_EXCLUSIVE);
opage = BufferGetPage(bucket_obuf);
oopaque = (HashPageOpaque) PageGetSpecialPointer(opage);
......@@ -1192,9 +1166,9 @@ _hash_finish_split(Relation rel, Buffer metabuf, Buffer obuf, Bucket obucket,
npageopaque = (HashPageOpaque) PageGetSpecialPointer(npage);
nbucket = npageopaque->hasho_bucket;
_hash_splitbucket_guts(rel, metabuf, obucket,
nbucket, obuf, bucket_nbuf, tidhtab,
maxbucket, highmask, lowmask);
_hash_splitbucket(rel, metabuf, obucket,
nbucket, obuf, bucket_nbuf, tidhtab,
maxbucket, highmask, lowmask);
_hash_relbuf(rel, bucket_nbuf);
LockBuffer(obuf, BUFFER_LOCK_UNLOCK);
......
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