* 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) 1996-2016, 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 1.35 2002/03/06 20:49:42 momjian Exp $
+ * src/backend/access/hash/hashpage.c
*
* 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.
+ * whether a page is an overflow page or a true bucket, the bucket
+ * number, and the block numbers of the preceding and following pages
+ * in the same bucket.
*
* The first page in a hash relation, page zero, is special -- it stores
* information describing the hash table; it is referred to as the
* "meta page." Pages one and higher store the actual data.
*
+ * There are also bitmap pages, which are not manipulated here;
+ * see hashovfl.c.
+ *
*-------------------------------------------------------------------------
*/
-
#include "postgres.h"
-#include "access/genam.h"
#include "access/hash.h"
#include "miscadmin.h"
#include "storage/lmgr.h"
+#include "storage/smgr.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);
+static bool _hash_alloc_buckets(Relation rel, BlockNumber firstblock,
+ uint32 nblocks);
+static void _hash_splitbucket(Relation rel, Buffer metabuf,
+ Bucket obucket, Bucket nbucket,
+ 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);
+
/*
- * 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.
- *
- * Note that our page locks are actual lockmanager locks, not buffer
- * locks (as are used by btree, for example). This is a good idea because
- * the algorithms are not deadlock-free, and we'd better be able to detect
- * and recover from deadlocks.
- *
- * Another important difference from btree is that a hash indexscan
- * retains both a lock and a buffer pin on the current index page
- * between hashgettuple() calls (btree keeps only a buffer pin).
- * Because of this, it's safe to do item deletions with only a regular
- * write lock on a hash page --- there cannot be an indexscan stopped on
- * the page being deleted, other than an indexscan of our own backend,
- * which will be taken care of by _hash_adjscans.
+ * We use high-concurrency locking on hash indexes (see README for an overview
+ * 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.
*/
+#define USELOCKING(rel) (!RELATION_IS_LOCAL(rel))
+
+
+/*
+ * _hash_getbuf() -- Get a buffer by block number for read or write.
+ *
+ * 'access' must be HASH_READ, HASH_WRITE, or HASH_NOLOCK.
+ * 'flags' is a bitwise OR of the allowed page types.
+ *
+ * This must be used only to fetch pages that are expected to be valid
+ * already. _hash_checkpage() is applied using the given flags.
+ *
+ * When this routine returns, the appropriate lock is set on the
+ * requested buffer and its reference count has been incremented
+ * (ie, the buffer is "locked and pinned").
+ *
+ * P_NEW is disallowed because this routine can only be used
+ * to access pages that are known to be before the filesystem EOF.
+ * Extending the index should be done with _hash_getnewbuf.
+ */
+Buffer
+_hash_getbuf(Relation rel, BlockNumber blkno, int access, int flags)
+{
+ Buffer buf;
+
+ if (blkno == P_NEW)
+ elog(ERROR, "hash AM does not use P_NEW");
+
+ buf = ReadBuffer(rel, blkno);
+ if (access != HASH_NOLOCK)
+ LockBuffer(buf, access);
-#define USELOCKING (!BuildingHash && !IsInitProcessingMode())
+ /* ref count and lock type are correct */
+ _hash_checkpage(rel, buf, flags);
+
+ return buf;
+}
/*
- * _hash_metapinit() -- Initialize the metadata page of a hash index,
- * the two buckets that we begin with and the initial
- * bitmap page.
+ * _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.
*/
-void
-_hash_metapinit(Relation rel)
+Buffer
+_hash_getbuf_with_condlock_cleanup(Relation rel, BlockNumber blkno, int flags)
{
- HashMetaPage metap;
- HashPageOpaque pageopaque;
- Buffer metabuf;
Buffer buf;
- Page pg;
- int nbuckets;
- uint32 nelem; /* number elements */
- uint32 lg2nelem; /* _hash_log2(nelem) */
- uint16 i;
- /* can't be sharing this with anyone, now... */
- if (USELOCKING)
- LockRelation(rel, AccessExclusiveLock);
-
- if (RelationGetNumberOfBlocks(rel) != 0)
- elog(ERROR, "Cannot initialize non-empty hash table %s",
- RelationGetRelationName(rel));
+ if (blkno == P_NEW)
+ elog(ERROR, "hash AM does not use P_NEW");
- metabuf = _hash_getbuf(rel, HASH_METAPAGE, HASH_WRITE);
- pg = BufferGetPage(metabuf);
- metap = (HashMetaPage) pg;
- _hash_pageinit(pg, BufferGetPageSize(metabuf));
+ buf = ReadBuffer(rel, blkno);
- 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 (!ConditionalLockBufferForCleanup(buf))
{
- if ((1 << i) < (metap->hashm_bsize -
- (MAXALIGN(sizeof(PageHeaderData)) +
- MAXALIGN(sizeof(HashPageOpaqueData)))))
- break;
+ ReleaseBuffer(buf);
+ return InvalidBuffer;
}
- 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));
+ /* ref count and lock type are correct */
- metap->hashm_spares[lg2nelem] = 2; /* lg2nelem + 1 */
- metap->hashm_spares[lg2nelem + 1] = 2; /* lg2nelem + 1 */
- metap->hashm_ovflpoint = 1; /* lg2nelem */
- metap->hashm_lastfreed = 2;
+ _hash_checkpage(rel, buf, flags);
- metap->hashm_maxbucket = metap->hashm_lowmask = 1; /* nbuckets - 1 */
- metap->hashm_highmask = 3; /* (nbuckets << 1) - 1 */
+ return buf;
+}
- 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;
+/*
+ * _hash_getinitbuf() -- Get and initialize a buffer by block number.
+ *
+ * This must be used only to fetch pages that are known to be before
+ * the index's filesystem EOF, but are to be filled from scratch.
+ * _hash_pageinit() is applied automatically. Otherwise it has
+ * effects similar to _hash_getbuf() with access = HASH_WRITE.
+ *
+ * When this routine returns, a write lock is set on the
+ * requested buffer and its reference count has been incremented
+ * (ie, the buffer is "locked and pinned").
+ *
+ * P_NEW is disallowed because this routine can only be used
+ * to access pages that are known to be before the filesystem EOF.
+ * Extending the index should be done with _hash_getnewbuf.
+ */
+Buffer
+_hash_getinitbuf(Relation rel, BlockNumber blkno)
+{
+ Buffer buf;
- /*
- * 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.");
+ if (blkno == P_NEW)
+ elog(ERROR, "hash AM does not use P_NEW");
- /* all done */
- _hash_wrtnorelbuf(metabuf);
+ buf = ReadBufferExtended(rel, MAIN_FORKNUM, blkno, RBM_ZERO_AND_LOCK,
+ NULL);
- /*
- * 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);
- }
+ /* ref count and lock type are correct */
- _hash_relbuf(rel, metabuf, HASH_WRITE);
+ /* initialize the page */
+ _hash_pageinit(BufferGetPage(buf), BufferGetPageSize(buf));
- if (USELOCKING)
- UnlockRelation(rel, AccessExclusiveLock);
+ return buf;
}
/*
- * _hash_getbuf() -- Get a buffer by block number for read or write.
+ * _hash_getnewbuf() -- Get a new page at the end of the index.
*
- * When this routine returns, the appropriate lock is set on the
- * requested buffer its reference count is correct.
+ * This has the same API as _hash_getinitbuf, except that we are adding
+ * a page to the index, and hence expect the page to be past the
+ * logical EOF. (However, we have to support the case where it isn't,
+ * since a prior try might have crashed after extending the filesystem
+ * EOF but before updating the metapage to reflect the added page.)
*
- * 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.
+ * It is caller's responsibility to ensure that only one process can
+ * 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_getbuf(Relation rel, BlockNumber blkno, int access)
+_hash_getnewbuf(Relation rel, BlockNumber blkno, ForkNumber forkNum)
{
+ BlockNumber nblocks = RelationGetNumberOfBlocksInFork(rel, forkNum);
Buffer buf;
if (blkno == P_NEW)
- elog(ERROR, "_hash_getbuf: internal error: hash AM does not use P_NEW");
- switch (access)
+ elog(ERROR, "hash AM does not use P_NEW");
+ if (blkno > nblocks)
+ elog(ERROR, "access to noncontiguous page in hash index \"%s\"",
+ RelationGetRelationName(rel));
+
+ /* smgr insists we use P_NEW to extend the relation */
+ if (blkno == nblocks)
{
- 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 = 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 = ReadBufferExtended(rel, forkNum, blkno, RBM_ZERO_AND_LOCK,
+ NULL);
}
- buf = ReadBuffer(rel, blkno);
/* ref count and lock type are correct */
+
+ /* initialize the page */
+ _hash_pageinit(BufferGetPage(buf), BufferGetPageSize(buf));
+
return buf;
}
/*
- * _hash_relbuf() -- release a locked buffer.
+ * _hash_getbuf_with_strategy() -- Get a buffer with nondefault strategy.
+ *
+ * This is identical to _hash_getbuf() but also allows a buffer access
+ * strategy to be specified. We use this for VACUUM operations.
*/
-void
-_hash_relbuf(Relation rel, Buffer buf, int access)
+Buffer
+_hash_getbuf_with_strategy(Relation rel, BlockNumber blkno,
+ int access, int flags,
+ BufferAccessStrategy bstrategy)
{
- BlockNumber blkno;
+ Buffer buf;
- blkno = BufferGetBlockNumber(buf);
+ if (blkno == P_NEW)
+ elog(ERROR, "hash AM does not use P_NEW");
- 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));
- }
+ buf = ReadBufferExtended(rel, MAIN_FORKNUM, blkno, RBM_NORMAL, bstrategy);
- ReleaseBuffer(buf);
+ if (access != HASH_NOLOCK)
+ LockBuffer(buf, access);
+
+ /* ref count and lock type are correct */
+
+ _hash_checkpage(rel, buf, flags);
+
+ return buf;
}
/*
- * _hash_wrtbuf() -- write a hash page to disk.
+ * _hash_relbuf() -- release a locked buffer.
*
- * 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.
+ * Lock and pin (refcount) are both dropped.
*/
void
-_hash_wrtbuf(Relation rel, Buffer buf)
+_hash_relbuf(Relation rel, Buffer buf)
{
- BlockNumber blkno;
-
- blkno = BufferGetBlockNumber(buf);
- WriteBuffer(buf);
- _hash_unsetpagelock(rel, blkno, HASH_WRITE);
+ UnlockReleaseBuffer(buf);
}
/*
- * _hash_wrtnorelbuf() -- write a hash page to disk, but do not release
- * our reference or lock.
+ * _hash_dropbuf() -- release an unlocked buffer.
*
- * It is an error to call _hash_wrtnorelbuf() without a write lock
- * or a reference to the buffer.
+ * This is used to unpin a buffer on which we hold no lock.
*/
void
-_hash_wrtnorelbuf(Buffer buf)
+_hash_dropbuf(Relation rel, Buffer buf)
{
- BlockNumber blkno;
+ ReleaseBuffer(buf);
+}
- blkno = BufferGetBlockNumber(buf);
- WriteNoReleaseBuffer(buf);
+/*
+ * _hash_dropscanbuf() -- release buffers used in scan.
+ *
+ * This routine unpins the buffers used during scan on which we
+ * hold no lock.
+ */
+void
+_hash_dropscanbuf(Relation rel, HashScanOpaque so)
+{
+ /* 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;
}
-Page
+/*
+ * _hash_chgbufaccess() -- Change the lock type on a buffer, without
+ * dropping our pin on it.
+ *
+ * from_access and to_access may be HASH_READ, HASH_WRITE, or HASH_NOLOCK,
+ * the last indicating that no buffer-level lock is held or wanted.
+ *
+ * When from_access == HASH_WRITE, we assume the buffer is dirty and tell
+ * bufmgr it must be written out. If the caller wants to release a write
+ * lock on a page that's not been modified, it's okay to pass from_access
+ * as HASH_READ (a bit ugly, but handy in some places).
+ */
+void
_hash_chgbufaccess(Relation rel,
- Buffer *bufp,
+ Buffer buf,
int from_access,
int to_access)
{
- BlockNumber blkno;
+ if (from_access == HASH_WRITE)
+ MarkBufferDirty(buf);
+ if (from_access != HASH_NOLOCK)
+ LockBuffer(buf, BUFFER_LOCK_UNLOCK);
+ if (to_access != HASH_NOLOCK)
+ LockBuffer(buf, to_access);
+}
+
+
+/*
+ * _hash_metapinit() -- Initialize the metadata page of a hash index,
+ * 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.
+ */
+uint32
+_hash_metapinit(Relation rel, double num_tuples, ForkNumber forkNum)
+{
+ HashMetaPage metap;
+ HashPageOpaque pageopaque;
+ Buffer metabuf;
+ Buffer buf;
+ Page pg;
+ int32 data_width;
+ int32 item_width;
+ int32 ffactor;
+ double dnumbuckets;
+ uint32 num_buckets;
+ uint32 log2_num_buckets;
+ uint32 i;
+
+ /* safety check */
+ if (RelationGetNumberOfBlocksInFork(rel, forkNum) != 0)
+ elog(ERROR, "cannot initialize non-empty hash index \"%s\"",
+ RelationGetRelationName(rel));
- blkno = BufferGetBlockNumber(*bufp);
+ /*
+ * 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 since the index datatype (i.e. uint32 hash key) is fixed-width.
+ */
+ 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;
+ /* keep to a sane range */
+ if (ffactor < 10)
+ ffactor = 10;
+
+ /*
+ * 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().
+ */
+ 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);
- switch (from_access)
+ 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_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(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 = HashGetMaxBitmapSize(pg);
+ /* find largest bitmap array size that will fit in page size */
+ for (i = _hash_log2(metap->hashm_bsize); i > 0; --i)
{
- 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));
+ if ((1 << i) <= metap->hashm_bsize)
break;
}
- *bufp = _hash_getbuf(rel, blkno, to_access);
- return BufferGetPage(*bufp);
+ 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 = index_getprocid(rel, 1, HASHPROC);
+
+ /*
+ * 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 = 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));
+
+ /* 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;
+
+ /*
+ * 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 < num_buckets; 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_nextblkno = InvalidBlockNumber;
+ pageopaque->hasho_bucket = i;
+ pageopaque->hasho_flag = LH_BUCKET_PAGE;
+ pageopaque->hasho_page_id = HASHO_PAGE_ID;
+ 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, num_buckets + 1, forkNum);
+
+ /* all done */
+ MarkBufferDirty(metabuf);
+ _hash_relbuf(rel, metabuf);
+
+ return num_buckets;
}
/*
- * _hash_pageinit() -- Initialize a new page.
+ * _hash_pageinit() -- Initialize a new hash index page.
*/
void
_hash_pageinit(Page page, Size 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;
- }
- }
-}
-
/*
- * Delete a hash index item.
- *
- * It is safe to delete an item after acquiring a regular WRITE lock on
- * the page, because no other backend can hold a READ lock on the page,
- * and that means no other backend currently has an indexscan stopped on
- * any item of the item being deleted. Our own backend might have such
- * an indexscan (in fact *will*, since that's how VACUUM found the item
- * in the first place), but _hash_adjscans will fix the scan position.
+ * Attempt to expand the hash table by creating one new bucket.
+ *
+ * This will silently do nothing if we don't get cleanup lock on old or
+ * new bucket.
+ *
+ * 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.
*/
void
-_hash_pagedel(Relation rel, ItemPointer tid)
+_hash_expandtable(Relation rel, Buffer metabuf)
{
- Buffer buf;
- Buffer metabuf;
- Page page;
- BlockNumber blkno;
- OffsetNumber offno;
HashMetaPage metap;
- HashPageOpaque opaque;
+ Bucket old_bucket;
+ Bucket new_bucket;
+ 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:
+
+ /*
+ * 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_chgbufaccess(rel, metabuf, HASH_NOLOCK, HASH_WRITE);
+
+ _hash_checkpage(rel, metabuf, LH_META_PAGE);
+ metap = HashPageGetMeta(BufferGetPage(metabuf));
+
+ /*
+ * Check to see if split is still needed; someone else might have already
+ * done one while we waited for the lock.
+ *
+ * Make sure this stays in sync with _hash_doinsert()
+ */
+ if (metap->hashm_ntuples <=
+ (double) metap->hashm_ffactor * (metap->hashm_maxbucket + 1))
+ goto fail;
+
+ /*
+ * 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.
+ *
+ * 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 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 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;
- blkno = ItemPointerGetBlockNumber(tid);
- offno = ItemPointerGetOffsetNumber(tid);
+ old_bucket = (new_bucket & metap->hashm_lowmask);
- buf = _hash_getbuf(rel, blkno, HASH_WRITE);
- page = BufferGetPage(buf);
- _hash_checkpage(page, LH_BUCKET_PAGE | LH_OVERFLOW_PAGE);
- opaque = (HashPageOpaque) PageGetSpecialPointer(page);
+ start_oblkno = BUCKET_TO_BLKNO(metap, old_bucket);
- PageIndexTupleDelete(page, offno);
- _hash_wrtnorelbuf(buf);
+ buf_oblkno = _hash_getbuf_with_condlock_cleanup(rel, start_oblkno, LH_BUCKET_PAGE);
+ if (!buf_oblkno)
+ goto fail;
- if (PageIsEmpty(page) && (opaque->hasho_flag & LH_OVERFLOW_PAGE))
+ opage = BufferGetPage(buf_oblkno);
+ oopaque = (HashPageOpaque) PageGetSpecialPointer(opage);
+
+ /*
+ * 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.
+ */
+ if (H_BUCKET_BEING_SPLIT(oopaque))
{
- buf = _hash_freeovflpage(rel, buf);
- if (BufferIsValid(buf))
- _hash_relbuf(rel, buf, HASH_WRITE);
+ /*
+ * 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;
+
+ /*
+ * 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);
+
+ _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;
}
- 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);
-}
+ /*
+ * 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;
-void
-_hash_expandtable(Relation rel, Buffer metabuf)
-{
- HashMetaPage metap;
- Bucket old_bucket;
- Bucket new_bucket;
- uint32 spare_ndx;
+ /* Release the metapage lock. */
+ _hash_chgbufaccess(rel, metabuf, HASH_READ, HASH_NOLOCK);
-/* elog(DEBUG, "_hash_expandtable: expanding..."); */
+ hashbucketcleanup(rel, old_bucket, buf_oblkno, start_oblkno, NULL,
+ maxbucket, highmask, lowmask, NULL, NULL, true,
+ NULL, NULL);
- metap = (HashMetaPage) BufferGetPage(metabuf);
- _hash_checkpage((Page) metap, LH_META_PAGE);
+ _hash_dropbuf(rel, buf_oblkno);
- metap = (HashMetaPage) _hash_chgbufaccess(rel, &metabuf, HASH_READ, HASH_WRITE);
- new_bucket = ++metap->hashm_maxbucket;
- metap = (HashMetaPage) _hash_chgbufaccess(rel, &metabuf, HASH_WRITE, HASH_READ);
- old_bucket = (metap->hashm_maxbucket & metap->hashm_lowmask);
+ 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 *
- * increases), we need to copy the current contents of the spare split
- * bucket to the next bucket.
+ * If the split point is increasing (hashm_maxbucket's log base 2
+ * increases), we need to allocate a new batch of bucket pages.
*/
- spare_ndx = _hash_log2(metap->hashm_maxbucket + 1);
+ spare_ndx = _hash_log2(new_bucket + 1);
if (spare_ndx > metap->hashm_ovflpoint)
{
+ Assert(spare_ndx == metap->hashm_ovflpoint + 1);
- metap = (HashMetaPage) _hash_chgbufaccess(rel, &metabuf, HASH_READ, HASH_WRITE);
- metap->hashm_spares[spare_ndx] = metap->hashm_spares[metap->hashm_ovflpoint];
- metap->hashm_ovflpoint = spare_ndx;
- metap = (HashMetaPage) _hash_chgbufaccess(rel, &metabuf, HASH_WRITE, HASH_READ);
+ /*
+ * 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_relbuf(rel, buf_oblkno);
+ goto fail;
+ }
}
- if (new_bucket > metap->hashm_highmask)
+ /*
+ * 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
+ * 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();
+
+ metap->hashm_maxbucket = new_bucket;
+ if (new_bucket > metap->hashm_highmask)
+ {
/* Starting a new doubling */
- metap = (HashMetaPage) _hash_chgbufaccess(rel, &metabuf, HASH_READ, HASH_WRITE);
metap->hashm_lowmask = metap->hashm_highmask;
metap->hashm_highmask = new_bucket | metap->hashm_lowmask;
- metap = (HashMetaPage) _hash_chgbufaccess(rel, &metabuf, HASH_WRITE, HASH_READ);
+ }
+ /*
+ * If the split point is increasing (hashm_maxbucket's log base 2
+ * increases), we need to adjust the hashm_spares[] array and
+ * hashm_ovflpoint so that future overflow pages will be created beyond
+ * this new batch of bucket pages.
+ */
+ if (spare_ndx > metap->hashm_ovflpoint)
+ {
+ metap->hashm_spares[spare_ndx] = metap->hashm_spares[metap->hashm_ovflpoint];
+ metap->hashm_ovflpoint = spare_ndx;
}
+
+ /* Done mucking with metapage */
+ END_CRIT_SECTION();
+
+ /*
+ * 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
+ * needs is to tell which of these two buckets to map hashkeys into.
+ */
+ maxbucket = metap->hashm_maxbucket;
+ highmask = metap->hashm_highmask;
+ lowmask = metap->hashm_lowmask;
+
+ /* Write out the metapage and drop lock, but keep pin */
+ _hash_chgbufaccess(rel, metabuf, HASH_WRITE, HASH_NOLOCK);
+
/* Relocate records to the new bucket */
- _hash_splitpage(rel, metabuf, old_bucket, new_bucket);
+ _hash_splitbucket(rel, metabuf,
+ old_bucket, new_bucket,
+ buf_oblkno, buf_nblkno,
+ maxbucket, highmask, lowmask);
+
+ return;
+
+ /* Here if decide not to split or fail to acquire old bucket lock */
+fail:
+
+ /* We didn't write the metapage, so just drop lock */
+ _hash_chgbufaccess(rel, metabuf, HASH_READ, HASH_NOLOCK);
+}
+
+
+/*
+ * _hash_alloc_buckets -- allocate a new splitpoint's worth of bucket pages
+ *
+ * This does not need to initialize the new bucket pages; we'll do that as
+ * each one is used by _hash_expandtable(). But we have to extend the logical
+ * EOF to the end of the splitpoint; this keeps smgr's idea of the EOF in
+ * sync with ours, so that we don't get complaints from smgr.
+ *
+ * We do this by writing a page of zeroes at the end of the splitpoint range.
+ * We expect that the filesystem will ensure that the intervening pages read
+ * as zeroes too. On many filesystems this "hole" will not be allocated
+ * immediately, which means that the index file may end up more fragmented
+ * than if we forced it all to be allocated now; but since we don't scan
+ * hash indexes sequentially anyway, that probably doesn't matter.
+ *
+ * XXX It's annoying that this code is executed with the metapage lock held.
+ * We need to interlock against _hash_getovflpage() adding a new overflow page
+ * concurrently, but it'd likely be better to use LockRelationForExtension
+ * for the purpose. OTOH, adding a splitpoint is a very infrequent operation,
+ * so it may not be worth worrying about.
+ *
+ * Returns TRUE if successful, or FALSE if allocation failed due to
+ * BlockNumber overflow.
+ */
+static bool
+_hash_alloc_buckets(Relation rel, BlockNumber firstblock, uint32 nblocks)
+{
+ BlockNumber lastblock;
+ char zerobuf[BLCKSZ];
+
+ lastblock = firstblock + nblocks - 1;
+
+ /*
+ * 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, MAIN_FORKNUM, lastblock, zerobuf, false);
+
+ return true;
}
/*
- * _hash_splitpage -- split 'obucket' into 'obucket' and 'nbucket'
+ * _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.
*
- * 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.
+ * 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_splitpage(Relation rel,
- Buffer metabuf,
- Bucket obucket,
- Bucket nbucket)
+_hash_splitbucket(Relation rel,
+ Buffer metabuf,
+ Bucket obucket,
+ Bucket nbucket,
+ Buffer obuf,
+ Buffer nbuf,
+ uint32 maxbucket,
+ uint32 highmask,
+ uint32 lowmask)
{
- 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);
+ 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 clear split-in-progress flag.
+ */
+ oopaque->hasho_flag |= LH_BUCKET_BEING_SPLIT;
+
npage = BufferGetPage(nbuf);
- /* initialize the new bucket */
- _hash_pageinit(npage, BufferGetPageSize(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 = InvalidBlockNumber;
nopaque->hasho_nextblkno = InvalidBlockNumber;
- nopaque->hasho_flag = LH_BUCKET_PAGE;
- nopaque->hasho_oaddr = InvalidOvflAddress;
nopaque->hasho_bucket = nbucket;
- _hash_wrtnorelbuf(nbuf);
+ 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);
/*
- * 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.
+ * 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. Outer loop iterates
+ * once per page in old bucket.
*/
- _hash_checkpage(opage, LH_BUCKET_PAGE);
- oopaque = (HashPageOpaque) PageGetSpecialPointer(opage);
- if (PageIsEmpty(opage))
+ for (;;)
{
- oblkno = oopaque->hasho_nextblkno;
- _hash_relbuf(rel, obuf, HASH_WRITE);
- if (!BlockNumberIsValid(oblkno))
+ BlockNumber oblkno;
+ OffsetNumber ooffnum;
+ OffsetNumber omaxoffnum;
+
+ /* Scan each tuple in old page */
+ omaxoffnum = PageGetMaxOffsetNumber(opage);
+ for (ooffnum = FirstOffsetNumber;
+ ooffnum <= omaxoffnum;
+ ooffnum = OffsetNumberNext(ooffnum))
{
+ IndexTuple itup;
+ Size itemsz;
+ Bucket bucket;
+ bool found = false;
+
+ /* skip dead tuples */
+ if (ItemIdIsDead(PageGetItemId(opage, ooffnum)))
+ continue;
+
/*
- * 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.
+ * 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_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);
- }
+ itup = (IndexTuple) PageGetItem(opage,
+ PageGetItemId(opage, ooffnum));
- /*
- * 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
- */
+ if (htab)
+ (void) hash_search(htab, &itup->t_tid, HASH_FIND, &found);
- /* 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))
+ if (found)
+ continue;
+
+ bucket = _hash_hashkey2bucket(_hash_get_indextuple_hashkey(itup),
+ maxbucket, highmask, lowmask);
+
+ if (bucket == nbucket)
{
+ IndexTuple new_itup;
+
/*
- * we ran out of tuples on this particular page, but we
- * have more overflow pages; re-init values.
+ * make a copy of index tuple as we have to scribble on it.
*/
- _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))
+ 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)
{
- elog(ERROR, "_hash_splitpage: empty ovfl page %d!",
- oblkno);
+ /* 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);
}
- ooffnum = FirstOffsetNumber;
- omaxoffnum = PageGetMaxOffsetNumber(opage);
+
+ /*
+ * 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
{
/*
- * 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.
+ * the tuple stays on this page, so nothing to do.
*/
- _hash_wrtbuf(rel, obuf);
- _hash_wrtbuf(rel, nbuf);
- _hash_squeezebucket(rel, metap, obucket);
- return;
+ Assert(bucket == obucket);
}
}
- /* 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);
+ oblkno = oopaque->hasho_nextblkno;
- 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));
+ /* 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);
- itemsz = MAXALIGN(itemsz);
+ /* Exit loop if no more overflow pages in old bucket */
+ if (!BlockNumberIsValid(oblkno))
+ break;
- 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);
- }
+ /* Else, advance to next old page */
+ obuf = _hash_getbuf(rel, oblkno, HASH_READ, LH_OVERFLOW_PAGE);
+ opage = BufferGetPage(obuf);
+ oopaque = (HashPageOpaque) PageGetSpecialPointer(opage);
+ }
- noffnum = OffsetNumberNext(PageGetMaxOffsetNumber(npage));
- if (PageAddItem(npage, (Item) hitem, itemsz, noffnum, LP_USED)
- == InvalidOffsetNumber)
- elog(ERROR, "_hash_splitpage: failed to add index item to %s",
- RelationGetRelationName(rel));
- _hash_wrtnorelbuf(nbuf);
+ /*
+ * 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);
+ }
- /*
- * 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(obuf);
- omaxoffnum = OffsetNumberPrev(omaxoffnum);
+ _hash_chgbufaccess(rel, bucket_obuf, HASH_NOLOCK, HASH_WRITE);
+ opage = BufferGetPage(bucket_obuf);
+ oopaque = (HashPageOpaque) PageGetSpecialPointer(opage);
- /*
- * 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);
+ _hash_chgbufaccess(rel, bucket_nbuf, HASH_NOLOCK, HASH_WRITE);
+ npage = BufferGetPage(bucket_nbuf);
+ nopaque = (HashPageOpaque) PageGetSpecialPointer(npage);
- /* check that we're not through the bucket chain */
- if (BufferIsInvalid(obuf))
- {
- _hash_wrtbuf(rel, nbuf);
- _hash_squeezebucket(rel, metap, obucket);
- return;
- }
+ oopaque->hasho_flag &= ~LH_BUCKET_BEING_SPLIT;
+ nopaque->hasho_flag &= ~LH_BUCKET_BEING_POPULATED;
- /*
- * 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
+ /*
+ * 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'.
- *
- * XXX any hash value from [0, nbucket-1] will map to this
- * bucket, which doesn't make sense to me.
- */
- 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;
+ }
+
+ /*
+ * 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.
+ */
+ if (!ConditionalLockBufferForCleanup(obuf))
+ {
+ hash_destroy(tidhtab);
+ return;
+ }
+ if (!ConditionalLockBufferForCleanup(bucket_nbuf))
+ {
+ _hash_chgbufaccess(rel, obuf, HASH_READ, HASH_NOLOCK);
+ hash_destroy(tidhtab);
+ return;
}
- /* NOTREACHED */
+
+ 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_relbuf(rel, bucket_nbuf);
+ _hash_chgbufaccess(rel, obuf, HASH_READ, HASH_NOLOCK);
+ hash_destroy(tidhtab);
}
projects / postgresql / blobdiff