* hashpage.c
* Hash table page management code for the Postgres hash access method
*
- * Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1996-2016, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
*
* IDENTIFICATION
- * $PostgreSQL: pgsql/src/backend/access/hash/hashpage.c,v 1.68 2007/05/30 20:11:51 tgl Exp $
+ * src/backend/access/hash/hashpage.c
*
* NOTES
* Postgres hash pages look like ordinary relation pages. The opaque
*/
#include "postgres.h"
-#include "access/genam.h"
#include "access/hash.h"
#include "miscadmin.h"
#include "storage/lmgr.h"
#include "storage/smgr.h"
-#include "utils/lsyscache.h"
static bool _hash_alloc_buckets(Relation rel, BlockNumber firstblock,
- uint32 nblocks);
+ uint32 nblocks);
static void _hash_splitbucket(Relation rel, Buffer metabuf,
Bucket obucket, Bucket nbucket,
- BlockNumber start_oblkno,
- BlockNumber start_nblkno,
+ Buffer obuf,
+ Buffer nbuf,
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);
/*
* of the locking rules). However, we can skip taking lmgr locks when the
* index is local to the current backend (ie, either temp or new in the
* current transaction). No one else can see it, so there's no reason to
- * take locks. We still take buffer-level locks, but not lmgr locks.
+ * take locks. We still take buffer-level locks, but not lmgr locks.
*/
#define USELOCKING(rel) (!RELATION_IS_LOCAL(rel))
-/*
- * _hash_getlock() -- Acquire an lmgr lock.
- *
- * 'whichlock' should be zero to acquire the split-control lock, or the
- * block number of a bucket's primary bucket page to acquire the per-bucket
- * lock. (See README for details of the use of these locks.)
- *
- * 'access' must be HASH_SHARE or HASH_EXCLUSIVE.
- */
-void
-_hash_getlock(Relation rel, BlockNumber whichlock, int access)
-{
- if (USELOCKING(rel))
- LockPage(rel, whichlock, access);
-}
-
-/*
- * _hash_try_getlock() -- Acquire an lmgr lock, but only if it's free.
- *
- * Same as above except we return FALSE without blocking if lock isn't free.
- */
-bool
-_hash_try_getlock(Relation rel, BlockNumber whichlock, int access)
-{
- if (USELOCKING(rel))
- return ConditionalLockPage(rel, whichlock, access);
- else
- return true;
-}
-
-/*
- * _hash_droplock() -- Release an lmgr lock.
- */
-void
-_hash_droplock(Relation rel, BlockNumber whichlock, int access)
-{
- if (USELOCKING(rel))
- UnlockPage(rel, whichlock, access);
-}
-
/*
* _hash_getbuf() -- Get a buffer by block number for read or write.
*
return buf;
}
+/*
+ * _hash_getbuf_with_condlock_cleanup() -- Try to get a buffer for cleanup.
+ *
+ * We read the page and try to acquire a cleanup lock. If we get it,
+ * we return the buffer; otherwise, we return InvalidBuffer.
+ */
+Buffer
+_hash_getbuf_with_condlock_cleanup(Relation rel, BlockNumber blkno, int flags)
+{
+ Buffer buf;
+
+ if (blkno == P_NEW)
+ elog(ERROR, "hash AM does not use P_NEW");
+
+ buf = ReadBuffer(rel, blkno);
+
+ if (!ConditionalLockBufferForCleanup(buf))
+ {
+ ReleaseBuffer(buf);
+ return InvalidBuffer;
+ }
+
+ /* ref count and lock type are correct */
+
+ _hash_checkpage(rel, buf, flags);
+
+ return buf;
+}
+
/*
* _hash_getinitbuf() -- Get and initialize a buffer by block number.
*
if (blkno == P_NEW)
elog(ERROR, "hash AM does not use P_NEW");
- buf = ReadOrZeroBuffer(rel, blkno);
-
- LockBuffer(buf, HASH_WRITE);
+ buf = ReadBufferExtended(rel, MAIN_FORKNUM, blkno, RBM_ZERO_AND_LOCK,
+ NULL);
/* ref count and lock type are correct */
* EOF but before updating the metapage to reflect the added page.)
*
* It is caller's responsibility to ensure that only one process can
- * extend the index at a time.
+ * extend the index at a time. In practice, this function is called
+ * only while holding write lock on the metapage, because adding a page
+ * is always associated with an update of metapage data.
*/
Buffer
-_hash_getnewbuf(Relation rel, BlockNumber blkno)
+_hash_getnewbuf(Relation rel, BlockNumber blkno, ForkNumber forkNum)
{
- BlockNumber nblocks = RelationGetNumberOfBlocks(rel);
+ BlockNumber nblocks = RelationGetNumberOfBlocksInFork(rel, forkNum);
Buffer buf;
if (blkno == P_NEW)
/* smgr insists we use P_NEW to extend the relation */
if (blkno == nblocks)
{
- buf = ReadBuffer(rel, P_NEW);
+ buf = ReadBufferExtended(rel, forkNum, P_NEW, RBM_NORMAL, NULL);
if (BufferGetBlockNumber(buf) != blkno)
elog(ERROR, "unexpected hash relation size: %u, should be %u",
BufferGetBlockNumber(buf), blkno);
+ LockBuffer(buf, HASH_WRITE);
}
else
- buf = ReadOrZeroBuffer(rel, blkno);
-
- LockBuffer(buf, HASH_WRITE);
+ {
+ buf = ReadBufferExtended(rel, forkNum, blkno, RBM_ZERO_AND_LOCK,
+ NULL);
+ }
/* ref count and lock type are correct */
if (blkno == P_NEW)
elog(ERROR, "hash AM does not use P_NEW");
- buf = ReadBufferWithStrategy(rel, blkno, bstrategy);
+ buf = ReadBufferExtended(rel, MAIN_FORKNUM, blkno, RBM_NORMAL, bstrategy);
if (access != HASH_NOLOCK)
LockBuffer(buf, access);
}
/*
- * _hash_wrtbuf() -- write a hash page to disk.
+ * _hash_dropscanbuf() -- release buffers used in scan.
*
- * This routine releases the lock held on the buffer and our refcount
- * for it. It is an error to call _hash_wrtbuf() without a write lock
- * and a pin on the buffer.
- *
- * NOTE: this routine should go away when/if hash indexes are WAL-ified.
- * The correct sequence of operations is to mark the buffer dirty, then
- * write the WAL record, then release the lock and pin; so marking dirty
- * can't be combined with releasing.
+ * This routine unpins the buffers used during scan on which we
+ * hold no lock.
*/
void
-_hash_wrtbuf(Relation rel, Buffer buf)
+_hash_dropscanbuf(Relation rel, HashScanOpaque so)
{
- MarkBufferDirty(buf);
- UnlockReleaseBuffer(buf);
+ /* release pin we hold on primary bucket page */
+ if (BufferIsValid(so->hashso_bucket_buf) &&
+ so->hashso_bucket_buf != so->hashso_curbuf)
+ _hash_dropbuf(rel, so->hashso_bucket_buf);
+ so->hashso_bucket_buf = InvalidBuffer;
+
+ /* release pin we hold on primary bucket page of bucket being split */
+ if (BufferIsValid(so->hashso_split_bucket_buf) &&
+ so->hashso_split_bucket_buf != so->hashso_curbuf)
+ _hash_dropbuf(rel, so->hashso_split_bucket_buf);
+ so->hashso_split_bucket_buf = InvalidBuffer;
+
+ /* release any pin we still hold */
+ if (BufferIsValid(so->hashso_curbuf))
+ _hash_dropbuf(rel, so->hashso_curbuf);
+ so->hashso_curbuf = InvalidBuffer;
+
+ /* reset split scan */
+ so->hashso_buc_populated = false;
+ so->hashso_buc_split = false;
}
/*
/*
* _hash_metapinit() -- Initialize the metadata page of a hash index,
- * the two buckets that we begin with and the initial
- * bitmap page.
+ * the initial buckets, and the initial bitmap page.
+ *
+ * The initial number of buckets is dependent on num_tuples, an estimate
+ * of the number of tuples to be loaded into the index initially. The
+ * chosen number of buckets is returned.
*
* 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)
+uint32
+_hash_metapinit(Relation rel, double num_tuples, ForkNumber forkNum)
{
HashMetaPage metap;
HashPageOpaque pageopaque;
int32 data_width;
int32 item_width;
int32 ffactor;
- uint16 i;
+ double dnumbuckets;
+ uint32 num_buckets;
+ uint32 log2_num_buckets;
+ uint32 i;
/* safety check */
- if (RelationGetNumberOfBlocks(rel) != 0)
+ if (RelationGetNumberOfBlocksInFork(rel, forkNum) != 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.
+ * as the user-settable fillfactor parameter says. We can compute it
+ * exactly since the index datatype (i.e. uint32 hash key) is fixed-width.
*/
- data_width = get_typavgwidth(RelationGetDescr(rel)->attrs[0]->atttypid,
- RelationGetDescr(rel)->attrs[0]->atttypmod);
+ data_width = sizeof(uint32);
item_width = MAXALIGN(sizeof(IndexTupleData)) + MAXALIGN(data_width) +
sizeof(ItemIdData); /* include the line pointer */
ffactor = RelationGetTargetPageUsage(rel, HASH_DEFAULT_FILLFACTOR) / item_width;
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.
+ * 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
+ * next power of 2, however, and always force at least 2 bucket pages. The
+ * upper limit is determined by considerations explained in
+ * _hash_expandtable().
*/
- metabuf = _hash_getnewbuf(rel, HASH_METAPAGE);
+ dnumbuckets = num_tuples / ffactor;
+ if (dnumbuckets <= 2.0)
+ num_buckets = 2;
+ else if (dnumbuckets >= (double) 0x40000000)
+ num_buckets = 0x40000000;
+ else
+ num_buckets = ((uint32) 1) << _hash_log2((uint32) dnumbuckets);
+
+ log2_num_buckets = _hash_log2(num_buckets);
+ Assert(num_buckets == (((uint32) 1) << log2_num_buckets));
+ Assert(log2_num_buckets < HASH_MAX_SPLITPOINTS);
+
+ /*
+ * We initialize the metapage, the first N 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.
+ */
+ metabuf = _hash_getnewbuf(rel, HASH_METAPAGE, forkNum);
pg = BufferGetPage(metabuf);
pageopaque = (HashPageOpaque) PageGetSpecialPointer(pg);
pageopaque->hasho_flag = LH_META_PAGE;
pageopaque->hasho_page_id = HASHO_PAGE_ID;
- metap = (HashMetaPage) pg;
+ metap = HashPageGetMeta(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);
+ metap->hashm_bsize = HashGetMaxBitmapSize(pg);
/* 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)))))
+ if ((1 << i) <= metap->hashm_bsize)
break;
}
Assert(i > 0);
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.
+ * 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. Since
+ * N is a power of 2, we can set the masks this way:
*/
- metap->hashm_maxbucket = metap->hashm_lowmask = 1; /* nbuckets - 1 */
- metap->hashm_highmask = 3; /* (nbuckets << 1) - 1 */
+ metap->hashm_maxbucket = metap->hashm_lowmask = num_buckets - 1;
+ metap->hashm_highmask = (num_buckets << 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;
+ /* Set up mapping for one spare page after the initial splitpoints */
+ metap->hashm_spares[log2_num_buckets] = 1;
+ metap->hashm_ovflpoint = log2_num_buckets;
metap->hashm_firstfree = 0;
/*
- * Initialize the first two buckets
+ * Release buffer lock on the metapage while we initialize buckets.
+ * Otherwise, we'll be in interrupt holdoff and the CHECK_FOR_INTERRUPTS
+ * won't accomplish anything. It's a bad idea to hold buffer locks for
+ * long intervals in any case, since that can block the bgwriter.
+ */
+ _hash_chgbufaccess(rel, metabuf, HASH_WRITE, HASH_NOLOCK);
+
+ /*
+ * Initialize the first N buckets
*/
- for (i = 0; i <= 1; i++)
+ for (i = 0; i < num_buckets; i++)
{
- buf = _hash_getnewbuf(rel, BUCKET_TO_BLKNO(metap, i));
+ /* Allow interrupts, in case N is huge */
+ CHECK_FOR_INTERRUPTS();
+
+ buf = _hash_getnewbuf(rel, BUCKET_TO_BLKNO(metap, i), forkNum);
pg = BufferGetPage(buf);
pageopaque = (HashPageOpaque) PageGetSpecialPointer(pg);
pageopaque->hasho_prevblkno = InvalidBlockNumber;
pageopaque->hasho_bucket = i;
pageopaque->hasho_flag = LH_BUCKET_PAGE;
pageopaque->hasho_page_id = HASHO_PAGE_ID;
- _hash_wrtbuf(rel, buf);
+ MarkBufferDirty(buf);
+ _hash_relbuf(rel, buf);
}
+ /* Now reacquire buffer lock on metapage */
+ _hash_chgbufaccess(rel, metabuf, HASH_NOLOCK, HASH_WRITE);
+
/*
* Initialize first bitmap page
*/
- _hash_initbitmap(rel, metap, 3);
+ _hash_initbitmap(rel, metap, num_buckets + 1, forkNum);
/* all done */
- _hash_wrtbuf(rel, metabuf);
+ MarkBufferDirty(metabuf);
+ _hash_relbuf(rel, metabuf);
+
+ return num_buckets;
}
/*
/*
* Attempt to expand the hash table by creating one new bucket.
*
- * This will silently do nothing if it cannot get the needed locks.
+ * This will silently do nothing if we don't get cleanup lock on old or
+ * new bucket.
*
- * The caller should hold no locks on the hash index.
+ * Complete the pending splits and remove the tuples from old bucket,
+ * if there are any left over from the previous split.
*
* The caller must hold a pin, but no lock, on the metapage buffer.
* The buffer is returned in the same state.
uint32 spare_ndx;
BlockNumber start_oblkno;
BlockNumber start_nblkno;
+ Buffer buf_nblkno;
+ Buffer buf_oblkno;
+ Page opage;
+ HashPageOpaque oopaque;
uint32 maxbucket;
uint32 highmask;
uint32 lowmask;
+restart_expand:
+
/*
- * Obtain the page-zero lock to assert the right to begin a split (see
- * README).
- *
- * Note: deadlock should be impossible here. Our own backend could only be
- * holding bucket sharelocks due to stopped indexscans; those will not
- * block other holders of the page-zero lock, who are only interested in
- * acquiring bucket sharelocks themselves. Exclusive bucket locks are
- * only taken here and in hashbulkdelete, and neither of these operations
- * needs any additional locks to complete. (If, due to some flaw in this
- * reasoning, we manage to deadlock anyway, it's okay to error out; the
- * index will be left in a consistent state.)
+ * Write-lock the meta page. It used to be necessary to acquire a
+ * heavyweight lock to begin a split, but that is no longer required.
*/
- _hash_getlock(rel, 0, HASH_EXCLUSIVE);
-
- /* Write-lock the meta page */
_hash_chgbufaccess(rel, metabuf, HASH_NOLOCK, HASH_WRITE);
_hash_checkpage(rel, metabuf, LH_META_PAGE);
- metap = (HashMetaPage) BufferGetPage(metabuf);
+ metap = HashPageGetMeta(BufferGetPage(metabuf));
/*
* Check to see if split is still needed; someone else might have already
goto fail;
/*
- * Can't split anymore if maxbucket has reached its maximum possible value.
+ * Can't split anymore if maxbucket has reached its maximum possible
+ * value.
*
* Ideally we'd allow bucket numbers up to UINT_MAX-1 (no higher because
* the calculation maxbucket+1 mustn't overflow). Currently we restrict
* to half that because of overflow looping in _hash_log2() and
* insufficient space in hashm_spares[]. It's moot anyway because an
- * index with 2^32 buckets would certainly overflow BlockNumber and
- * hence _hash_alloc_buckets() would fail, but if we supported buckets
- * smaller than a disk block then this would be an independent constraint.
+ * index with 2^32 buckets would certainly overflow BlockNumber and hence
+ * _hash_alloc_buckets() would fail, but if we supported buckets smaller
+ * than a disk block then this would be an independent constraint.
+ *
+ * If you change this, see also the maximum initial number of buckets in
+ * _hash_metapinit().
*/
if (metap->hashm_maxbucket >= (uint32) 0x7FFFFFFE)
goto fail;
/*
- * Determine which bucket is to be split, and attempt to lock the old
- * bucket. If we can't get the lock, give up.
+ * Determine which bucket is to be split, and attempt to take cleanup lock
+ * on the old bucket. If we can't get the lock, give up.
+ *
+ * The cleanup lock protects us not only against other backends, but
+ * against our own backend as well.
*
- * The lock protects us against other backends, but not against our own
- * backend. Must check for active scans separately.
+ * The cleanup lock is mainly to protect the split from concurrent
+ * inserts. See src/backend/access/hash/README, Lock Definitions for
+ * further details. Due to this locking restriction, if there is any
+ * pending scan, the split will give up which is not good, but harmless.
*/
new_bucket = metap->hashm_maxbucket + 1;
start_oblkno = BUCKET_TO_BLKNO(metap, old_bucket);
- if (_hash_has_active_scan(rel, old_bucket))
+ buf_oblkno = _hash_getbuf_with_condlock_cleanup(rel, start_oblkno, LH_BUCKET_PAGE);
+ if (!buf_oblkno)
goto fail;
- if (!_hash_try_getlock(rel, start_oblkno, HASH_EXCLUSIVE))
- goto fail;
+ opage = BufferGetPage(buf_oblkno);
+ oopaque = (HashPageOpaque) PageGetSpecialPointer(opage);
/*
- * Likewise lock the new bucket (should never fail).
- *
- * Note: it is safe to compute the new bucket's blkno here, even though
- * we may still need to update the BUCKET_TO_BLKNO mapping. This is
- * because the current value of hashm_spares[hashm_ovflpoint] correctly
- * shows where we are going to put a new splitpoint's worth of buckets.
+ * We want to finish the split from a bucket as there is no apparent
+ * benefit by not doing so and it will make the code complicated to finish
+ * the split that involves multiple buckets considering the case where new
+ * split also fails. We don't need to consider the new bucket for
+ * completing the split here as it is not possible that a re-split of new
+ * bucket starts when there is still a pending split from old bucket.
*/
- start_nblkno = BUCKET_TO_BLKNO(metap, new_bucket);
+ if (H_BUCKET_BEING_SPLIT(oopaque))
+ {
+ /*
+ * Copy bucket mapping info now; refer the comment in code below where
+ * we copy this information before calling _hash_splitbucket to see
+ * why this is okay.
+ */
+ maxbucket = metap->hashm_maxbucket;
+ highmask = metap->hashm_highmask;
+ lowmask = metap->hashm_lowmask;
- if (_hash_has_active_scan(rel, new_bucket))
- elog(ERROR, "scan in progress on supposedly new bucket");
+ /*
+ * Release the lock on metapage and old_bucket, before completing the
+ * split.
+ */
+ _hash_chgbufaccess(rel, metabuf, HASH_READ, HASH_NOLOCK);
+ _hash_chgbufaccess(rel, buf_oblkno, HASH_READ, HASH_NOLOCK);
- if (!_hash_try_getlock(rel, start_nblkno, HASH_EXCLUSIVE))
- elog(ERROR, "could not get lock on supposedly new bucket");
+ _hash_finish_split(rel, metabuf, buf_oblkno, old_bucket, maxbucket,
+ highmask, lowmask);
+
+ /* release the pin on old buffer and retry for expand. */
+ _hash_dropbuf(rel, buf_oblkno);
+
+ goto restart_expand;
+ }
+
+ /*
+ * Clean the tuples remained from the previous split. This operation
+ * requires cleanup lock and we already have one on the old bucket, so
+ * let's do it. We also don't want to allow further splits from the bucket
+ * till the garbage of previous split is cleaned. This has two
+ * advantages; first, it helps in avoiding the bloat due to garbage and
+ * second is, during cleanup of bucket, we are always sure that the
+ * garbage tuples belong to most recently split bucket. On the contrary,
+ * if we allow cleanup of bucket after meta page is updated to indicate
+ * the new split and before the actual split, the cleanup operation won't
+ * be able to decide whether the tuple has been moved to the newly created
+ * bucket and ended up deleting such tuples.
+ */
+ if (H_NEEDS_SPLIT_CLEANUP(oopaque))
+ {
+ /*
+ * Copy bucket mapping info now; refer to the comment in code below
+ * where we copy this information before calling _hash_splitbucket
+ * to see why this is okay.
+ */
+ maxbucket = metap->hashm_maxbucket;
+ highmask = metap->hashm_highmask;
+ lowmask = metap->hashm_lowmask;
+
+ /* Release the metapage lock. */
+ _hash_chgbufaccess(rel, metabuf, HASH_READ, HASH_NOLOCK);
+
+ hashbucketcleanup(rel, old_bucket, buf_oblkno, start_oblkno, NULL,
+ maxbucket, highmask, lowmask, NULL, NULL, true,
+ NULL, NULL);
+
+ _hash_dropbuf(rel, buf_oblkno);
+
+ goto restart_expand;
+ }
+
+ /*
+ * There shouldn't be any active scan on new bucket.
+ *
+ * Note: it is safe to compute the new bucket's blkno here, even though we
+ * may still need to update the BUCKET_TO_BLKNO mapping. This is because
+ * the current value of hashm_spares[hashm_ovflpoint] correctly shows
+ * where we are going to put a new splitpoint's worth of buckets.
+ */
+ start_nblkno = BUCKET_TO_BLKNO(metap, new_bucket);
/*
* If the split point is increasing (hashm_maxbucket's log base 2
if (spare_ndx > metap->hashm_ovflpoint)
{
Assert(spare_ndx == metap->hashm_ovflpoint + 1);
+
/*
- * The number of buckets in the new splitpoint is equal to the
- * total number already in existence, i.e. new_bucket. Currently
- * this maps one-to-one to blocks required, but someday we may need
- * a more complicated calculation here.
+ * The number of buckets in the new splitpoint is equal to the total
+ * number already in existence, i.e. new_bucket. Currently this maps
+ * one-to-one to blocks required, but someday we may need a more
+ * complicated calculation here.
*/
if (!_hash_alloc_buckets(rel, start_nblkno, new_bucket))
{
/* can't split due to BlockNumber overflow */
- _hash_droplock(rel, start_oblkno, HASH_EXCLUSIVE);
- _hash_droplock(rel, start_nblkno, HASH_EXCLUSIVE);
+ _hash_relbuf(rel, buf_oblkno);
goto fail;
}
}
/*
- * Okay to proceed with split. Update the metapage bucket mapping info.
+ * Physically allocate the new bucket's primary page. We want to do this
+ * before changing the metapage's mapping info, in case we can't get the
+ * disk space. Ideally, we don't need to check for cleanup lock on new
+ * bucket as no other backend could find this bucket unless meta page is
+ * updated. However, it is good to be consistent with old bucket locking.
+ */
+ buf_nblkno = _hash_getnewbuf(rel, start_nblkno, MAIN_FORKNUM);
+ if (!IsBufferCleanupOK(buf_nblkno))
+ {
+ _hash_relbuf(rel, buf_oblkno);
+ _hash_relbuf(rel, buf_nblkno);
+ 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
* Copy bucket mapping info now; this saves re-accessing the meta page
* inside _hash_splitbucket's inner loop. Note that once we drop the
* split lock, other splits could begin, so these values might be out of
- * date before _hash_splitbucket finishes. That's okay, since all it
+ * date before _hash_splitbucket finishes. That's okay, since all it
* needs is to tell which of these two buckets to map hashkeys into.
*/
maxbucket = metap->hashm_maxbucket;
/* Write out the metapage and drop lock, but keep pin */
_hash_chgbufaccess(rel, metabuf, HASH_WRITE, HASH_NOLOCK);
- /* Release split lock; okay for other splits to occur now */
- _hash_droplock(rel, 0, HASH_EXCLUSIVE);
-
/* Relocate records to the new bucket */
- _hash_splitbucket(rel, metabuf, old_bucket, new_bucket,
- start_oblkno, start_nblkno,
+ _hash_splitbucket(rel, metabuf,
+ old_bucket, new_bucket,
+ buf_oblkno, buf_nblkno,
maxbucket, highmask, lowmask);
- /* Release bucket locks, allowing others to access them */
- _hash_droplock(rel, start_oblkno, HASH_EXCLUSIVE);
- _hash_droplock(rel, start_nblkno, HASH_EXCLUSIVE);
-
return;
/* Here if decide not to split or fail to acquire old bucket lock */
/* We didn't write the metapage, so just drop lock */
_hash_chgbufaccess(rel, metabuf, HASH_READ, HASH_NOLOCK);
-
- /* Release split lock */
- _hash_droplock(rel, 0, HASH_EXCLUSIVE);
}
static bool
_hash_alloc_buckets(Relation rel, BlockNumber firstblock, uint32 nblocks)
{
- BlockNumber lastblock;
+ BlockNumber lastblock;
char zerobuf[BLCKSZ];
lastblock = firstblock + nblocks - 1;
/*
- * Check for overflow in block number calculation; if so, we cannot
- * extend the index anymore.
+ * Check for overflow in block number calculation; if so, we cannot extend
+ * the index anymore.
*/
if (lastblock < firstblock || lastblock == InvalidBlockNumber)
return false;
MemSet(zerobuf, 0, sizeof(zerobuf));
RelationOpenSmgr(rel);
- smgrextend(rel->rd_smgr, lastblock, zerobuf, rel->rd_istemp);
+ smgrextend(rel->rd_smgr, MAIN_FORKNUM, lastblock, zerobuf, false);
return true;
}
* 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
+ * The caller must hold cleanup 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.)
+ *
+ * Split needs to retain pin on primary bucket pages of both old and new
+ * buckets till end of operation. This is to prevent vacuum from starting
+ * while a split is in progress.
+ *
+ * In addition, the caller must have created the new bucket's base page,
+ * which is passed in buffer nbuf, pinned and write-locked. That lock and
+ * pin are released here. (The API is set up this way because we must do
+ * _hash_getnewbuf() before releasing the metapage write lock. So instead of
+ * passing the new bucket's start block number, we pass an actual buffer.)
*/
static void
_hash_splitbucket(Relation rel,
Buffer metabuf,
Bucket obucket,
Bucket nbucket,
- BlockNumber start_oblkno,
- BlockNumber start_nblkno,
+ Buffer obuf,
+ Buffer nbuf,
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);
+ HashPageOpaque oopaque;
+ HashPageOpaque nopaque;
- /*
- * 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, LH_BUCKET_PAGE);
opage = BufferGetPage(obuf);
oopaque = (HashPageOpaque) PageGetSpecialPointer(opage);
- nblkno = start_nblkno;
- nbuf = _hash_getnewbuf(rel, nblkno);
+ /*
+ * Mark the old bucket to indicate that split is in progress. At
+ * operation end, we clear split-in-progress flag.
+ */
+ oopaque->hasho_flag |= LH_BUCKET_BEING_SPLIT;
+
npage = BufferGetPage(nbuf);
- /* initialize the new bucket's primary page */
+ /*
+ * initialize the new bucket's primary page and mark it to indicate that
+ * split is in progress.
+ */
nopaque = (HashPageOpaque) PageGetSpecialPointer(npage);
nopaque->hasho_prevblkno = InvalidBlockNumber;
nopaque->hasho_nextblkno = InvalidBlockNumber;
nopaque->hasho_bucket = nbucket;
- nopaque->hasho_flag = LH_BUCKET_PAGE;
+ 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;
+ Page opage;
+ Page npage;
+ HashPageOpaque oopaque;
+ HashPageOpaque nopaque;
+
+ bucket_obuf = obuf;
+ opage = BufferGetPage(obuf);
+ oopaque = (HashPageOpaque) PageGetSpecialPointer(opage);
+
+ bucket_nbuf = nbuf;
+ npage = BufferGetPage(nbuf);
+ nopaque = (HashPageOpaque) PageGetSpecialPointer(npage);
+
/*
* 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.
+ * adding overflow pages to the new bucket as needed. Outer loop iterates
+ * once per page in old bucket.
*/
- 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)
+ BlockNumber oblkno;
+ OffsetNumber ooffnum;
+ OffsetNumber omaxoffnum;
+
+ /* Scan each tuple in old page */
+ omaxoffnum = PageGetMaxOffsetNumber(opage);
+ for (ooffnum = FirstOffsetNumber;
+ ooffnum <= omaxoffnum;
+ ooffnum = OffsetNumberNext(ooffnum))
{
- /* at end of page, but check for an(other) overflow page */
- oblkno = oopaque->hasho_nextblkno;
- if (!BlockNumberIsValid(oblkno))
- break;
+ IndexTuple itup;
+ Size itemsz;
+ Bucket bucket;
+ bool found = false;
+
+ /* skip dead tuples */
+ if (ItemIdIsDead(PageGetItemId(opage, ooffnum)))
+ continue;
/*
- * we ran out of tuples on this particular page, but we have more
- * overflow pages; advance to next page.
+ * Before inserting a tuple, probe the hash table containing TIDs
+ * of tuples belonging to new bucket, if we find a match, then
+ * skip that tuple, else fetch the item's hash key (conveniently
+ * stored in the item) and determine which bucket it now belongs
+ * in.
*/
- _hash_wrtbuf(rel, obuf);
-
- obuf = _hash_getbuf(rel, oblkno, HASH_WRITE, LH_OVERFLOW_PAGE);
- opage = BufferGetPage(obuf);
- oopaque = (HashPageOpaque) PageGetSpecialPointer(opage);
- ooffnum = FirstOffsetNumber;
- omaxoffnum = PageGetMaxOffsetNumber(opage);
- continue;
- }
+ itup = (IndexTuple) PageGetItem(opage,
+ PageGetItemId(opage, ooffnum));
- /*
- * 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);
+ if (htab)
+ (void) hash_search(htab, &itup->t_tid, HASH_FIND, &found);
- bucket = _hash_hashkey2bucket(_hash_datum2hashkey(rel, datum),
- maxbucket, highmask, lowmask);
+ if (found)
+ continue;
- 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);
+ bucket = _hash_hashkey2bucket(_hash_get_indextuple_hashkey(itup),
+ maxbucket, highmask, lowmask);
- if (PageGetFreeSpace(npage) < itemsz)
+ if (bucket == nbucket)
+ {
+ IndexTuple new_itup;
+
+ /*
+ * make a copy of index tuple as we have to scribble on it.
+ */
+ new_itup = CopyIndexTuple(itup);
+
+ /*
+ * mark the index tuple as moved by split, such tuples are
+ * skipped by scan if there is split in progress for a bucket.
+ */
+ new_itup->t_info |= INDEX_MOVED_BY_SPLIT_MASK;
+
+ /*
+ * 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(*new_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, (nbuf == bucket_nbuf) ? true : false);
+ npage = BufferGetPage(nbuf);
+ nopaque = (HashPageOpaque) PageGetSpecialPointer(npage);
+ }
+
+ /*
+ * Insert tuple on new page, using _hash_pgaddtup to ensure
+ * correct ordering by hashkey. This is a tad inefficient
+ * since we may have to shuffle itempointers repeatedly.
+ * Possible future improvement: accumulate all the items for
+ * the new page and qsort them before insertion.
+ */
+ (void) _hash_pgaddtup(rel, nbuf, itemsz, new_itup);
+
+ /* be tidy */
+ pfree(new_itup);
+ }
+ else
{
- /* 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);
- npage = BufferGetPage(nbuf);
- /* we don't need nopaque within the loop */
+ /*
+ * the tuple stays on this page, so nothing to do.
+ */
+ Assert(bucket == obucket);
}
+ }
- 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));
+ oblkno = oopaque->hasho_nextblkno;
- /*
- * 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);
- }
+ /* retain the pin on the old primary bucket */
+ if (obuf == bucket_obuf)
+ _hash_chgbufaccess(rel, obuf, HASH_READ, HASH_NOLOCK);
else
+ _hash_relbuf(rel, obuf);
+
+ /* Exit loop if no more overflow pages in old bucket */
+ if (!BlockNumberIsValid(oblkno))
+ break;
+
+ /* Else, advance to next old page */
+ obuf = _hash_getbuf(rel, oblkno, HASH_READ, LH_OVERFLOW_PAGE);
+ opage = BufferGetPage(obuf);
+ oopaque = (HashPageOpaque) PageGetSpecialPointer(opage);
+ }
+
+ /*
+ * We're at the end of the old bucket chain, so we're done partitioning
+ * the tuples. Mark the old and new buckets to indicate split is
+ * finished.
+ *
+ * To avoid deadlocks due to locking order of buckets, first lock the old
+ * bucket and then the new bucket.
+ */
+ if (nbuf == bucket_nbuf)
+ _hash_chgbufaccess(rel, bucket_nbuf, HASH_WRITE, HASH_NOLOCK);
+ else
+ {
+ MarkBufferDirty(nbuf);
+ _hash_relbuf(rel, nbuf);
+ }
+
+ _hash_chgbufaccess(rel, bucket_obuf, HASH_NOLOCK, HASH_WRITE);
+ opage = BufferGetPage(bucket_obuf);
+ oopaque = (HashPageOpaque) PageGetSpecialPointer(opage);
+
+ _hash_chgbufaccess(rel, bucket_nbuf, HASH_NOLOCK, HASH_WRITE);
+ npage = BufferGetPage(bucket_nbuf);
+ nopaque = (HashPageOpaque) PageGetSpecialPointer(npage);
+
+ oopaque->hasho_flag &= ~LH_BUCKET_BEING_SPLIT;
+ nopaque->hasho_flag &= ~LH_BUCKET_BEING_POPULATED;
+
+ /*
+ * After the split is finished, mark the old bucket to indicate that it
+ * contains deletable tuples. Vacuum will clear split-cleanup flag after
+ * deleting such tuples.
+ */
+ oopaque->hasho_flag |= LH_BUCKET_NEEDS_SPLIT_CLEANUP;
+
+ /*
+ * now write the buffers, here we don't release the locks as caller is
+ * responsible to release locks.
+ */
+ MarkBufferDirty(bucket_obuf);
+ MarkBufferDirty(bucket_nbuf);
+}
+
+/*
+ * _hash_finish_split() -- Finish the previously interrupted split operation
+ *
+ * To complete the split operation, we form the hash table of TIDs in new
+ * bucket which is then used by split operation to skip tuples that are
+ * already moved before the split operation was previously interrupted.
+ *
+ * The caller must hold a pin, but no lock, on the metapage and old bucket's
+ * primay page buffer. The buffers are returned in the same state. (The
+ * metapage is only touched if it becomes necessary to add or remove overflow
+ * pages.)
+ */
+void
+_hash_finish_split(Relation rel, Buffer metabuf, Buffer obuf, Bucket obucket,
+ uint32 maxbucket, uint32 highmask, uint32 lowmask)
+{
+ HASHCTL hash_ctl;
+ HTAB *tidhtab;
+ Buffer bucket_nbuf = InvalidBuffer;
+ Buffer nbuf;
+ Page npage;
+ BlockNumber nblkno;
+ BlockNumber bucket_nblkno;
+ HashPageOpaque npageopaque;
+ Bucket nbucket;
+ bool found;
+
+ /* Initialize hash tables used to track TIDs */
+ memset(&hash_ctl, 0, sizeof(hash_ctl));
+ hash_ctl.keysize = sizeof(ItemPointerData);
+ hash_ctl.entrysize = sizeof(ItemPointerData);
+ hash_ctl.hcxt = CurrentMemoryContext;
+
+ tidhtab =
+ hash_create("bucket ctids",
+ 256, /* arbitrary initial size */
+ &hash_ctl,
+ HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
+
+ bucket_nblkno = nblkno = _hash_get_newblock_from_oldbucket(rel, obucket);
+
+ /*
+ * Scan the new bucket and build hash table of TIDs
+ */
+ for (;;)
+ {
+ OffsetNumber noffnum;
+ OffsetNumber nmaxoffnum;
+
+ nbuf = _hash_getbuf(rel, nblkno, HASH_READ,
+ LH_BUCKET_PAGE | LH_OVERFLOW_PAGE);
+
+ /* remember the primary bucket buffer to acquire cleanup lock on it. */
+ if (nblkno == bucket_nblkno)
+ bucket_nbuf = nbuf;
+
+ npage = BufferGetPage(nbuf);
+ npageopaque = (HashPageOpaque) PageGetSpecialPointer(npage);
+
+ /* Scan each tuple in new page */
+ nmaxoffnum = PageGetMaxOffsetNumber(npage);
+ for (noffnum = FirstOffsetNumber;
+ noffnum <= nmaxoffnum;
+ noffnum = OffsetNumberNext(noffnum))
{
- /*
- * 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);
+ IndexTuple itup;
+
+ /* Fetch the item's TID and insert it in hash table. */
+ itup = (IndexTuple) PageGetItem(npage,
+ PageGetItemId(npage, noffnum));
+
+ (void) hash_search(tidhtab, &itup->t_tid, HASH_ENTER, &found);
+
+ Assert(!found);
}
+
+ nblkno = npageopaque->hasho_nextblkno;
+
+ /*
+ * release our write lock without modifying buffer and ensure to
+ * retain the pin on primary bucket.
+ */
+ if (nbuf == bucket_nbuf)
+ _hash_chgbufaccess(rel, nbuf, HASH_READ, HASH_NOLOCK);
+ else
+ _hash_relbuf(rel, nbuf);
+
+ /* Exit loop if no more overflow pages in new bucket */
+ if (!BlockNumberIsValid(nblkno))
+ break;
}
/*
- * 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.
+ * Conditionally get the cleanup lock on old and new buckets to perform
+ * the split operation. If we don't get the cleanup locks, silently give
+ * up and next insertion on old bucket will try again to complete the
+ * split.
*/
- _hash_wrtbuf(rel, obuf);
- _hash_wrtbuf(rel, nbuf);
+ if (!ConditionalLockBufferForCleanup(obuf))
+ {
+ hash_destroy(tidhtab);
+ return;
+ }
+ if (!ConditionalLockBufferForCleanup(bucket_nbuf))
+ {
+ _hash_chgbufaccess(rel, obuf, HASH_READ, HASH_NOLOCK);
+ hash_destroy(tidhtab);
+ return;
+ }
+
+ npage = BufferGetPage(bucket_nbuf);
+ npageopaque = (HashPageOpaque) PageGetSpecialPointer(npage);
+ nbucket = npageopaque->hasho_bucket;
+
+ _hash_splitbucket_guts(rel, metabuf, obucket,
+ nbucket, obuf, bucket_nbuf, tidhtab,
+ maxbucket, highmask, lowmask);
- _hash_squeezebucket(rel, obucket, start_oblkno, NULL);
+ _hash_relbuf(rel, bucket_nbuf);
+ _hash_chgbufaccess(rel, obuf, HASH_READ, HASH_NOLOCK);
+ hash_destroy(tidhtab);
}
projects / postgresql / blobdiff