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/*-------------------------------------------------------------------------
*
* gist.h
* The public API for GiST indexes. This API is exposed to
* individuals implementing GiST indexes, so backward-incompatible
* changes should be made with care.
*
*
* Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* src/include/access/gist.h
*
*-------------------------------------------------------------------------
*/
#ifndef GIST_H
#define GIST_H
#include "access/itup.h"
#include "access/transam.h"
#include "access/xlog.h"
#include "access/xlogdefs.h"
#include "storage/block.h"
#include "storage/bufpage.h"
#include "utils/relcache.h"
/*
* amproc indexes for GiST indexes.
*/
#define GIST_CONSISTENT_PROC 1
#define GIST_UNION_PROC 2
#define GIST_COMPRESS_PROC 3
#define GIST_DECOMPRESS_PROC 4
#define GIST_PENALTY_PROC 5
#define GIST_PICKSPLIT_PROC 6
#define GIST_EQUAL_PROC 7
#define GIST_DISTANCE_PROC 8
#define GIST_FETCH_PROC 9
#define GIST_OPTIONS_PROC 10
#define GIST_SORTSUPPORT_PROC 11
#define GISTNProcs 11
/*
* Page opaque data in a GiST index page.
*/
#define F_LEAF (1 << 0) /* leaf page */
#define F_DELETED (1 << 1) /* the page has been deleted */
#define F_TUPLES_DELETED (1 << 2) /* some tuples on the page were
* deleted */
#define F_FOLLOW_RIGHT (1 << 3) /* page to the right has no downlink */
#define F_HAS_GARBAGE (1 << 4) /* some tuples on the page are dead,
* but not deleted yet */
/*
* NSN (node sequence number) is a special-purpose LSN which is stored on each
* index page in GISTPageOpaqueData and updated only during page splits. By
* recording the parent's LSN in GISTSearchItem.parentlsn, it is possible to
* detect concurrent child page splits by checking if parentlsn < child's NSN,
* and handle them properly. The child page's LSN is insufficient for this
* purpose since it is updated for every page change.
*/
typedef XLogRecPtr GistNSN;
/*
* A fake LSN / NSN value used during index builds. Must be smaller than any
* real or fake (unlogged) LSN generated after the index build completes so
* that all splits are considered complete.
*/
#define GistBuildLSN ((XLogRecPtr) 1)
/*
* For on-disk compatibility with pre-9.3 servers, NSN is stored as two
* 32-bit fields on disk, same as LSNs.
*/
typedef PageXLogRecPtr PageGistNSN;
typedef struct GISTPageOpaqueData
{
PageGistNSN nsn; /* this value must change on page split */
BlockNumber rightlink; /* next page if any */
uint16 flags; /* see bit definitions above */
uint16 gist_page_id; /* for identification of GiST indexes */
} GISTPageOpaqueData;
typedef GISTPageOpaqueData *GISTPageOpaque;
/*
* Maximum possible sizes for GiST index tuple and index key. Calculation is
* based on assumption that GiST page should fit at least 4 tuples. In theory,
* GiST index can be functional when page can fit 3 tuples. But that seems
* rather inefficient, so we use a bit conservative estimate.
*
* The maximum size of index key is true for unicolumn index. Therefore, this
* estimation should be used to figure out which maximum size of GiST index key
* makes sense at all. For multicolumn indexes, user might be able to tune
* key size using opclass parameters.
*/
#define GISTMaxIndexTupleSize \
MAXALIGN_DOWN((BLCKSZ - SizeOfPageHeaderData - sizeof(GISTPageOpaqueData)) / \
4 - sizeof(ItemIdData))
#define GISTMaxIndexKeySize \
(GISTMaxIndexTupleSize - MAXALIGN(sizeof(IndexTupleData)))
/*
* The page ID is for the convenience of pg_filedump and similar utilities,
* which otherwise would have a hard time telling pages of different index
* types apart. It should be the last 2 bytes on the page. This is more or
* less "free" due to alignment considerations.
*/
#define GIST_PAGE_ID 0xFF81
/*
* This is the Split Vector to be returned by the PickSplit method.
* PickSplit should fill the indexes of tuples to go to the left side into
* spl_left[], and those to go to the right into spl_right[] (note the method
* is responsible for palloc'ing both of these arrays!). The tuple counts
* go into spl_nleft/spl_nright, and spl_ldatum/spl_rdatum must be set to
* the union keys for each side.
*
* If spl_ldatum_exists and spl_rdatum_exists are true, then we are performing
* a "secondary split" using a non-first index column. In this case some
* decisions have already been made about a page split, and the set of tuples
* being passed to PickSplit is just the tuples about which we are undecided.
* spl_ldatum/spl_rdatum then contain the union keys for the tuples already
* chosen to go left or right. Ideally the PickSplit method should take those
* keys into account while deciding what to do with the remaining tuples, ie
* it should try to "build out" from those unions so as to minimally expand
* them. If it does so, it should union the given tuples' keys into the
* existing spl_ldatum/spl_rdatum values rather than just setting those values
* from scratch, and then set spl_ldatum_exists/spl_rdatum_exists to false to
* show it has done this.
*
* If the PickSplit method fails to clear spl_ldatum_exists/spl_rdatum_exists,
* the core GiST code will make its own decision about how to merge the
* secondary-split results with the previously-chosen tuples, and will then
* recompute the union keys from scratch. This is a workable though often not
* optimal approach.
*/
typedef struct GIST_SPLITVEC
{
OffsetNumber *spl_left; /* array of entries that go left */
int spl_nleft; /* size of this array */
Datum spl_ldatum; /* Union of keys in spl_left */
bool spl_ldatum_exists; /* true, if spl_ldatum already exists. */
OffsetNumber *spl_right; /* array of entries that go right */
int spl_nright; /* size of the array */
Datum spl_rdatum; /* Union of keys in spl_right */
bool spl_rdatum_exists; /* true, if spl_rdatum already exists. */
} GIST_SPLITVEC;
/*
* An entry on a GiST node. Contains the key, as well as its own
* location (rel,page,offset) which can supply the matching pointer.
* leafkey is a flag to tell us if the entry is in a leaf node.
*/
typedef struct GISTENTRY
{
Datum key;
Relation rel;
Page page;
OffsetNumber offset;
bool leafkey;
} GISTENTRY;
#define GistPageGetOpaque(page) ( (GISTPageOpaque) PageGetSpecialPointer(page) )
#define GistPageIsLeaf(page) ( GistPageGetOpaque(page)->flags & F_LEAF)
#define GIST_LEAF(entry) (GistPageIsLeaf((entry)->page))
#define GistPageIsDeleted(page) ( GistPageGetOpaque(page)->flags & F_DELETED)
#define GistTuplesDeleted(page) ( GistPageGetOpaque(page)->flags & F_TUPLES_DELETED)
#define GistMarkTuplesDeleted(page) ( GistPageGetOpaque(page)->flags |= F_TUPLES_DELETED)
#define GistClearTuplesDeleted(page) ( GistPageGetOpaque(page)->flags &= ~F_TUPLES_DELETED)
#define GistPageHasGarbage(page) ( GistPageGetOpaque(page)->flags & F_HAS_GARBAGE)
#define GistMarkPageHasGarbage(page) ( GistPageGetOpaque(page)->flags |= F_HAS_GARBAGE)
#define GistClearPageHasGarbage(page) ( GistPageGetOpaque(page)->flags &= ~F_HAS_GARBAGE)
#define GistFollowRight(page) ( GistPageGetOpaque(page)->flags & F_FOLLOW_RIGHT)
#define GistMarkFollowRight(page) ( GistPageGetOpaque(page)->flags |= F_FOLLOW_RIGHT)
#define GistClearFollowRight(page) ( GistPageGetOpaque(page)->flags &= ~F_FOLLOW_RIGHT)
#define GistPageGetNSN(page) ( PageXLogRecPtrGet(GistPageGetOpaque(page)->nsn))
#define GistPageSetNSN(page, val) ( PageXLogRecPtrSet(GistPageGetOpaque(page)->nsn, val))
/*
* On a deleted page, we store this struct. A deleted page doesn't contain any
* tuples, so we don't use the normal page layout with line pointers. Instead,
* this struct is stored right after the standard page header. pd_lower points
* to the end of this struct. If we add fields to this struct in the future, we
* can distinguish the old and new formats by pd_lower.
*/
typedef struct GISTDeletedPageContents
{
/* last xid which could see the page in a scan */
FullTransactionId deleteXid;
} GISTDeletedPageContents;
static inline void
GistPageSetDeleted(Page page, FullTransactionId deletexid)
{
Assert(PageIsEmpty(page));
GistPageGetOpaque(page)->flags |= F_DELETED;
((PageHeader) page)->pd_lower = MAXALIGN(SizeOfPageHeaderData) + sizeof(GISTDeletedPageContents);
((GISTDeletedPageContents *) PageGetContents(page))->deleteXid = deletexid;
}
static inline FullTransactionId
GistPageGetDeleteXid(Page page)
{
Assert(GistPageIsDeleted(page));
/* Is the deleteXid field present? */
if (((PageHeader) page)->pd_lower >= MAXALIGN(SizeOfPageHeaderData) +
offsetof(GISTDeletedPageContents, deleteXid) + sizeof(FullTransactionId))
{
return ((GISTDeletedPageContents *) PageGetContents(page))->deleteXid;
}
else
return FullTransactionIdFromEpochAndXid(0, FirstNormalTransactionId);
}
/*
* Vector of GISTENTRY structs; user-defined methods union and picksplit
* take it as one of their arguments
*/
typedef struct
{
int32 n; /* number of elements */
GISTENTRY vector[FLEXIBLE_ARRAY_MEMBER];
} GistEntryVector;
#define GEVHDRSZ (offsetof(GistEntryVector, vector))
/*
* macro to initialize a GISTENTRY
*/
#define gistentryinit(e, k, r, pg, o, l) \
do { (e).key = (k); (e).rel = (r); (e).page = (pg); \
(e).offset = (o); (e).leafkey = (l); } while (0)
#endif /* GIST_H */