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Preliminary cleanup for hash index code (doesn't attack the locking problem
yet). Fix a couple of bugs that would only appear if multiple bitmap pages are used, including a buffer reference leak and incorrect computation of bit indexes. Get rid of 'overflow address' concept, which accomplished nothing except obfuscating the code and creating a risk of failure due to limited range of offset field. Rename some misleadingly-named fields and routines, and improve documentation.
This commit is contained in:
Tom Lane
@@ -7,7 +7,7 @@
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* Portions Copyright (c) 1996-2003, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* $Id: hash.h,v 1.49 2003/08/04 02:40:10 momjian Exp $
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* $Id: hash.h,v 1.50 2003/09/01 20:26:34 tgl Exp $
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*
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* NOTES
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* modeled after Margo Seltzer's hash implementation for unix.
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@@ -24,43 +24,18 @@
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#include "fmgr.h"
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/*
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* An overflow page is a spare page allocated for storing data whose
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* bucket doesn't have room to store it. We use overflow pages rather
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* than just splitting the bucket because there is a linear order in
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* the way we split buckets. In other words, if there isn't enough space
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* in the bucket itself, put it in an overflow page.
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*
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* Overflow page addresses are stored in form: (Splitnumber, Page offset).
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*
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* A splitnumber is the number of the generation where the table doubles
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* in size. The ovflpage's offset within the splitnumber; offsets start
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* at 1.
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*
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* We convert the stored bitmap address into a page address with the
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* macro OADDR_OF(S, O) where S is the splitnumber and O is the page
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* offset.
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* Mapping from hash bucket number to physical block number of bucket's
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* starting page. Beware of multiple evaluations of argument! Also notice
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* macro's implicit dependency on "metap".
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*/
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typedef uint32 Bucket;
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typedef bits16 OverflowPageAddress;
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typedef uint32 SplitNumber;
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typedef uint32 PageOffset;
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/* A valid overflow address will always have a page offset >= 1 */
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#define InvalidOvflAddress 0
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#define SPLITSHIFT 11
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#define SPLITMASK 0x7FF
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#define SPLITNUM(N) ((SplitNumber)(((uint32)(N)) >> SPLITSHIFT))
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#define OPAGENUM(N) ((PageOffset)((N) & SPLITMASK))
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#define OADDR_OF(S,O) ((OverflowPageAddress)((uint32)((uint32)(S) << SPLITSHIFT) + (O)))
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#define BUCKET_TO_BLKNO(B) \
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((Bucket) ((B) + ((B) ? metap->hashm_spares[_hash_log2((B)+1)-1] : 0)) + 1)
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#define OADDR_TO_BLKNO(B) \
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((BlockNumber) \
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(BUCKET_TO_BLKNO ( (1 << SPLITNUM((B))) -1 ) + OPAGENUM((B))));
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((BlockNumber) ((B) + ((B) ? metap->hashm_spares[_hash_log2((B)+1)-1] : 0)) + 1)
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/*
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* Special space for hash index pages.
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*
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* hasho_flag tells us which type of page we're looking at. For
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* example, knowing overflow pages from bucket pages is necessary
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* information when you're deleting tuples from a page. If all the
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@@ -69,7 +44,6 @@ typedef uint32 PageOffset;
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* the tuples are deleted from a bucket page, no additional action is
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* necessary.
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*/
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#define LH_UNUSED_PAGE (0)
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#define LH_OVERFLOW_PAGE (1 << 0)
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#define LH_BUCKET_PAGE (1 << 1)
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@@ -78,9 +52,9 @@ typedef uint32 PageOffset;
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typedef struct HashPageOpaqueData
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{
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bits16 hasho_flag; /* is this page a bucket or ovfl */
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bits16 hasho_flag; /* page type code, see above */
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Bucket hasho_bucket; /* bucket number this pg belongs to */
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OverflowPageAddress hasho_oaddr; /* ovfl address of this ovfl pg */
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bits16 hasho_oaddr; /* no longer used; delete someday */
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BlockNumber hasho_nextblkno; /* next ovfl blkno */
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BlockNumber hasho_prevblkno; /* previous ovfl (or bucket) blkno */
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} HashPageOpaqueData;
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@@ -91,10 +65,8 @@ typedef HashPageOpaqueData *HashPageOpaque;
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* ScanOpaqueData is used to remember which buffers we're currently
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* examining in the scan. We keep these buffers locked and pinned and
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* recorded in the opaque entry of the scan in order to avoid doing a
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* ReadBuffer() for every tuple in the index. This avoids semop() calls,
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* which are expensive.
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* ReadBuffer() for every tuple in the index.
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*/
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typedef struct HashScanOpaqueData
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{
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Buffer hashso_curbuf;
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@@ -113,60 +85,55 @@ typedef HashScanOpaqueData *HashScanOpaque;
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#define HASH_VERSION 0
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/*
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* NCACHED is used to set the array sizeof spares[] & bitmaps[].
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* Spares[] holds the number of overflow pages currently allocated at or
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* before a certain splitpoint. For example, if spares[3] = 7 then there are
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* 7 ovflpages before splitpoint 3 (compare BUCKET_TO_BLKNO macro). The
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* value in spares[ovflpoint] increases as overflow pages are added at the
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* end of the index. Once ovflpoint increases (ie, we have actually allocated
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* the bucket pages belonging to that splitpoint) the number of spares at the
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* prior splitpoint cannot change anymore.
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*
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* Spares[] is used to hold the number overflow pages currently
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* allocated at a certain splitpoint. For example, if spares[3] = 7
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* then there are a maximum of 7 ovflpages available at splitpoint 3.
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* The value in spares[] will change as ovflpages are added within
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* a splitpoint.
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* ovflpages that have been recycled for reuse can be found by looking at
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* bitmaps that are stored within ovflpages dedicated for the purpose.
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* The blknos of these bitmap pages are kept in bitmaps[]; nmaps is the
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* number of currently existing bitmaps.
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*
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* Within a splitpoint, one can find which ovflpages are available and
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* which are used by looking at a bitmaps that are stored on the ovfl
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* pages themselves. There is at least one bitmap for every splitpoint's
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* ovflpages. Bitmaps[] contains the ovflpage addresses of the ovflpages
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* that hold the ovflpage bitmaps.
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*
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* The reason that the size is restricted to NCACHED (32) is because
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* the bitmaps are 16 bits: upper 5 represent the splitpoint, lower 11
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* indicate the page number within the splitpoint. Since there are
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* only 5 bits to store the splitpoint, there can only be 32 splitpoints.
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* Both spares[] and bitmaps[] use splitpoints as there indices, so there
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* can only be 32 of them.
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* The limitation on the size of spares[] comes from the fact that there's
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* no point in having more than 2^32 buckets with only uint32 hashcodes.
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* There is no particularly good reason for bitmaps[] to be the same size,
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* but we're stuck with that until we want to force an initdb. (With 8K
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* block size, 32 bitmaps limit us to 8 Gb of overflow space...)
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*/
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#define NCACHED 32
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#define HASH_MAX_SPLITPOINTS 32
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#define HASH_MAX_BITMAPS 32
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typedef struct HashMetaPageData
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{
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PageHeaderData hashm_phdr; /* pad for page header (do not use) */
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uint32 hashm_magic; /* magic no. for hash tables */
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uint32 hashm_version; /* version ID */
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uint32 hashm_nkeys; /* number of keys stored in the table */
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uint16 hashm_ffactor; /* fill factor */
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uint16 hashm_bsize; /* bucket size (bytes) - must be a power
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uint32 hashm_ntuples; /* number of tuples stored in the table */
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uint16 hashm_ffactor; /* target fill factor (tuples/bucket) */
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uint16 hashm_bsize; /* index page size (bytes) - must be a power
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* of 2 */
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uint16 hashm_bshift; /* bucket shift */
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uint16 hashm_bmsize; /* bitmap array size (bytes) - must be a
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* power of 2 */
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uint16 hashm_bshift; /* log2(bsize) */
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uint16 hashm_bmsize; /* bitmap array size (bytes) - must be
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* exactly half of hashm_bsize */
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uint32 hashm_maxbucket; /* ID of maximum bucket in use */
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uint32 hashm_highmask; /* mask to modulo into entire table */
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uint32 hashm_lowmask; /* mask to modulo into lower half of table */
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uint32 hashm_ovflpoint;/* pageno. from which ovflpgs being
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uint32 hashm_ovflpoint;/* splitpoint from which ovflpgs being
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* allocated */
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uint32 hashm_lastfreed; /* last ovflpage freed */
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uint32 hashm_nmaps; /* Initial number of bitmaps */
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uint32 hashm_spares[NCACHED]; /* spare pages available at
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* splitpoints */
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BlockNumber hashm_mapp[NCACHED]; /* blknumbers of ovfl page maps */
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uint32 hashm_firstfree; /* lowest-number free ovflpage (bit#) */
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uint32 hashm_nmaps; /* number of bitmap pages */
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uint32 hashm_spares[HASH_MAX_SPLITPOINTS]; /* spare pages before
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* each splitpoint */
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BlockNumber hashm_mapp[HASH_MAX_BITMAPS]; /* blknos of ovfl bitmaps */
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RegProcedure hashm_procid; /* hash procedure id from pg_proc */
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} HashMetaPageData;
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typedef HashMetaPageData *HashMetaPage;
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extern bool BuildingHash;
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typedef struct HashItemData
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{
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IndexTupleData hash_itup;
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@@ -178,31 +145,33 @@ typedef HashItemData *HashItem;
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* Constants
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*/
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#define DEFAULT_FFACTOR 300
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#define SPLITMAX 8
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#define BYTE_TO_BIT 3 /* 2^3 bits/byte */
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#define INT_TO_BYTE 2 /* 2^2 bytes/int */
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#define INT_TO_BIT 5 /* 2^5 bits/int */
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#define ALL_SET ((uint32) ~0)
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/*
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* bitmap pages do not contain tuples. they do contain the standard
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* Bitmap pages do not contain tuples. They do contain the standard
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* page headers and trailers; however, everything in between is a
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* giant bit array. the number of bits that fit on a page obviously
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* depends on the page size and the header/trailer overhead.
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* giant bit array. The number of bits that fit on a page obviously
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* depends on the page size and the header/trailer overhead. In the
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* present implementation, we use exactly half of a page for bitmap,
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* so that we have a power-of-2 bits per page.
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*
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* The fact that the metapage has separate bsize and bmsize fields,
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* but only one bshift field, is a design error that ought to be fixed.
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*/
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#define BMPGSZ_BYTE(metap) ((metap)->hashm_bmsize)
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#define BMPGSZ_BIT(metap) ((metap)->hashm_bmsize << BYTE_TO_BIT)
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#define BMPG_SHIFT(metap) ((metap)->hashm_bshift - 1 + BYTE_TO_BIT)
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#define BMPG_MASK(metap) (BMPGSZ_BIT(metap) - 1)
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#define HashPageGetBitmap(pg) \
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((uint32 *) (((char *) (pg)) + MAXALIGN(sizeof(PageHeaderData))))
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/*
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* The number of bits in an ovflpage bitmap which
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* tells which ovflpages are empty versus in use (NOT the number of
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* bits in an overflow page *address* bitmap).
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* The number of bits in an ovflpage bitmap word.
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*/
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#define BITS_PER_MAP 32 /* Number of bits in ovflpage bitmap */
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#define BITS_PER_MAP 32 /* Number of bits in uint32 */
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/* Given the address of the beginning of a big map, clear/set the nth bit */
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/* Given the address of the beginning of a bit map, clear/set the nth bit */
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#define CLRBIT(A, N) ((A)[(N)/BITS_PER_MAP] &= ~(1<<((N)%BITS_PER_MAP)))
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#define SETBIT(A, N) ((A)[(N)/BITS_PER_MAP] |= (1<<((N)%BITS_PER_MAP)))
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#define ISSET(A, N) ((A)[(N)/BITS_PER_MAP] & (1<<((N)%BITS_PER_MAP)))
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@@ -213,18 +182,9 @@ typedef HashItemData *HashItem;
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#define HASH_READ 0
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#define HASH_WRITE 1
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/*
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* In general, the hash code tries to localize its knowledge about page
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* layout to a couple of routines. However, we need a special value to
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* indicate "no page number" in those places where we expect page numbers.
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*/
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#define P_NONE 0
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/*
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* Strategy number. There's only one valid strategy for hashing: equality.
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*/
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#define HTEqualStrategyNumber 1
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#define HTMaxStrategyNumber 1
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@@ -233,9 +193,11 @@ typedef HashItemData *HashItem;
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* us with an amproc procudure for hashing a key of the new type.
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* Since we only have one such proc in amproc, it's number 1.
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*/
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#define HASHPROC 1
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extern bool BuildingHash;
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/* public routines */
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extern Datum hashbuild(PG_FUNCTION_ARGS);
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@@ -276,36 +238,32 @@ extern Datum hash_any(register const unsigned char *k, register int keylen);
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/* hashinsert.c */
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extern InsertIndexResult _hash_doinsert(Relation rel, HashItem hitem);
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/* hashovfl.c */
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extern Buffer _hash_addovflpage(Relation rel, Buffer *metabufp, Buffer buf);
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extern Buffer _hash_freeovflpage(Relation rel, Buffer ovflbuf);
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extern int32 _hash_initbitmap(Relation rel, HashMetaPage metap, int32 pnum,
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int32 nbits, int32 ndx);
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extern Buffer _hash_addovflpage(Relation rel, Buffer metabuf, Buffer buf);
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extern BlockNumber _hash_freeovflpage(Relation rel, Buffer ovflbuf);
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extern void _hash_initbitmap(Relation rel, HashMetaPage metap,
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BlockNumber blkno);
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extern void _hash_squeezebucket(Relation rel, HashMetaPage metap,
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Bucket bucket);
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/* hashpage.c */
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extern void _hash_metapinit(Relation rel);
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extern Buffer _hash_getbuf(Relation rel, BlockNumber blkno, int access);
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extern void _hash_relbuf(Relation rel, Buffer buf, int access);
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extern void _hash_wrtbuf(Relation rel, Buffer buf);
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extern void _hash_wrtnorelbuf(Buffer buf);
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extern Page _hash_chgbufaccess(Relation rel, Buffer *bufp, int from_access,
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extern void _hash_chgbufaccess(Relation rel, Buffer buf, int from_access,
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int to_access);
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extern void _hash_pageinit(Page page, Size size);
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extern void _hash_pagedel(Relation rel, ItemPointer tid);
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extern void _hash_expandtable(Relation rel, Buffer metabuf);
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/* hashscan.c */
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extern void _hash_regscan(IndexScanDesc scan);
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extern void _hash_dropscan(IndexScanDesc scan);
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extern void _hash_adjscans(Relation rel, ItemPointer tid);
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extern void AtEOXact_hash(void);
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/* hashsearch.c */
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extern void _hash_search(Relation rel, int keysz, ScanKey scankey,
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Buffer *bufP, HashMetaPage metap);
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@@ -314,7 +272,6 @@ extern bool _hash_first(IndexScanDesc scan, ScanDirection dir);
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extern bool _hash_step(IndexScanDesc scan, Buffer *bufP, ScanDirection dir,
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Buffer metabuf);
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/* hashutil.c */
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extern ScanKey _hash_mkscankey(Relation rel, IndexTuple itup);
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extern void _hash_freeskey(ScanKey skey);
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@@ -324,7 +281,6 @@ extern Bucket _hash_call(Relation rel, HashMetaPage metap, Datum key);
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extern uint32 _hash_log2(uint32 num);
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extern void _hash_checkpage(Page page, int flags);
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/* hash.c */
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extern void hash_redo(XLogRecPtr lsn, XLogRecord *record);
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extern void hash_undo(XLogRecPtr lsn, XLogRecord *record);
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