1
/*-------------------------------------------------------------------------
4
* Standard POSTGRES buffer page definitions.
7
* Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
8
* Portions Copyright (c) 1994, Regents of the University of California
10
* $PostgreSQL: pgsql/src/include/storage/bufpage.h,v 1.63 2004-12-31 22:03:42 pgsql Exp $
12
*-------------------------------------------------------------------------
17
#include "storage/buf.h"
18
#include "storage/bufmgr.h"
19
#include "storage/item.h"
20
#include "storage/itemid.h"
21
#include "storage/off.h"
22
#include "access/xlog.h"
25
* A postgres disk page is an abstraction layered on top of a postgres
26
* disk block (which is simply a unit of i/o, see block.h).
28
* specifically, while a disk block can be unformatted, a postgres
29
* disk page is always a slotted page of the form:
31
* +----------------+---------------------------------+
32
* | PageHeaderData | linp1 linp2 linp3 ... |
33
* +-----------+----+---------------------------------+
35
* +-----------+--------------------------------------+
39
* +-------------+------------------------------------+
41
* +-------------+------------------+-----------------+
42
* | ... tuple3 tuple2 tuple1 | "special space" |
43
* +--------------------------------+-----------------+
46
* a page is full when nothing can be added between pd_lower and
49
* all blocks written out by an access method must be disk pages.
53
* obviously, a page is not formatted before it is initialized with by
58
* linp1..N form an ItemId array. ItemPointers point into this array
59
* rather than pointing directly to a tuple. Note that OffsetNumbers
60
* conventionally start at 1, not 0.
62
* tuple1..N are added "backwards" on the page. because a tuple's
63
* ItemPointer points to its ItemId entry rather than its actual
64
* byte-offset position, tuples can be physically shuffled on a page
65
* whenever the need arises.
67
* AM-generic per-page information is kept in PageHeaderData.
69
* AM-specific per-page data (if any) is kept in the area marked "special
70
* space"; each AM has an "opaque" structure defined somewhere that is
71
* stored as the page trailer. an access method should always
72
* initialize its pages with PageInit and then set its own opaque
80
* location (byte offset) within a page.
82
* note that this is actually limited to 2^15 because we have limited
83
* ItemIdData.lp_off and ItemIdData.lp_len to 15 bits (see itemid.h).
85
typedef uint16 LocationIndex;
89
* disk page organization
91
* space management information generic to any page
93
* pd_lsn - identifies xlog record for last change to this page.
95
* pd_lower - offset to start of free space.
96
* pd_upper - offset to end of free space.
97
* pd_special - offset to start of special space.
98
* pd_pagesize_version - size in bytes and page layout version number.
100
* The LSN is used by the buffer manager to enforce the basic rule of WAL:
101
* "thou shalt write xlog before data". A dirty buffer cannot be dumped
102
* to disk until xlog has been flushed at least as far as the page's LSN.
103
* We also store the TLI for identification purposes (it is not clear that
104
* this is actually necessary, but it seems like a good idea).
106
* The page version number and page size are packed together into a single
107
* uint16 field. This is for historical reasons: before PostgreSQL 7.3,
108
* there was no concept of a page version number, and doing it this way
109
* lets us pretend that pre-7.3 databases have page version number zero.
110
* We constrain page sizes to be multiples of 256, leaving the low eight
111
* bits available for a version number.
113
* Minimum possible page size is perhaps 64B to fit page header, opaque space
114
* and a minimal tuple; of course, in reality you want it much bigger, so
115
* the constraint on pagesize mod 256 is not an important restriction.
116
* On the high end, we can only support pages up to 32KB because lp_off/lp_len
119
typedef struct PageHeaderData
121
/* XXX LSN is member of *any* block, not only page-organized ones */
122
XLogRecPtr pd_lsn; /* LSN: next byte after last byte of xlog
123
* record for last change to this page */
124
TimeLineID pd_tli; /* TLI of last change */
125
LocationIndex pd_lower; /* offset to start of free space */
126
LocationIndex pd_upper; /* offset to end of free space */
127
LocationIndex pd_special; /* offset to start of special space */
128
uint16 pd_pagesize_version;
129
ItemIdData pd_linp[1]; /* beginning of line pointer array */
132
typedef PageHeaderData *PageHeader;
135
* Page layout version number 0 is for pre-7.3 Postgres releases.
136
* Releases 7.3 and 7.4 use 1, denoting a new HeapTupleHeader layout.
137
* Release 8.0 changed the HeapTupleHeader layout again.
139
#define PG_PAGE_LAYOUT_VERSION 2
142
/* ----------------------------------------------------------------
143
* page support macros
144
* ----------------------------------------------------------------
149
* True iff page is valid.
151
#define PageIsValid(page) PointerIsValid(page)
154
* line pointer does not count as part of header
156
#define SizeOfPageHeaderData (offsetof(PageHeaderData, pd_linp[0]))
160
* returns true iff no itemid has been allocated on the page
162
#define PageIsEmpty(page) \
163
(((PageHeader) (page))->pd_lower <= SizeOfPageHeaderData)
167
* returns true iff page has not been initialized (by PageInit)
169
#define PageIsNew(page) (((PageHeader) (page))->pd_upper == 0)
173
* Returns an item identifier of a page.
175
#define PageGetItemId(page, offsetNumber) \
176
((ItemId) (&((PageHeader) (page))->pd_linp[(offsetNumber) - 1]))
180
* To be used in case the page does not contain item pointers.
182
#define PageGetContents(page) \
183
((char *) (&((PageHeader) (page))->pd_linp[0]))
186
* macros to access page size info
192
* True iff the page size is valid.
194
#define PageSizeIsValid(pageSize) ((pageSize) == BLCKSZ)
198
* Returns the page size of a page.
200
* this can only be called on a formatted page (unlike
201
* BufferGetPageSize, which can be called on an unformatted page).
202
* however, it can be called on a page that is not stored in a buffer.
204
#define PageGetPageSize(page) \
205
((Size) (((PageHeader) (page))->pd_pagesize_version & (uint16) 0xFF00))
208
* PageGetPageLayoutVersion
209
* Returns the page layout version of a page.
211
#define PageGetPageLayoutVersion(page) \
212
(((PageHeader) (page))->pd_pagesize_version & 0x00FF)
215
* PageSetPageSizeAndVersion
216
* Sets the page size and page layout version number of a page.
218
* We could support setting these two values separately, but there's
219
* no real need for it at the moment.
221
#define PageSetPageSizeAndVersion(page, size, version) \
223
AssertMacro(((size) & 0xFF00) == (size)), \
224
AssertMacro(((version) & 0x00FF) == (version)), \
225
((PageHeader) (page))->pd_pagesize_version = (size) | (version) \
229
* page special data macros
234
* Returns size of special space on a page.
236
#define PageGetSpecialSize(page) \
237
((uint16) (PageGetPageSize(page) - ((PageHeader)(page))->pd_special))
240
* PageGetSpecialPointer
241
* Returns pointer to special space on a page.
243
#define PageGetSpecialPointer(page) \
245
AssertMacro(PageIsValid(page)), \
246
(char *) ((char *) (page) + ((PageHeader) (page))->pd_special) \
251
* Retrieves an item on the given page.
254
* This does not change the status of any of the resources passed.
255
* The semantics may change in the future.
257
#define PageGetItem(page, itemId) \
259
AssertMacro(PageIsValid(page)), \
260
AssertMacro((itemId)->lp_flags & LP_USED), \
261
(Item)(((char *)(page)) + (itemId)->lp_off) \
266
* Returns the page size within a buffer.
269
* Assumes buffer is valid.
271
* The buffer can be a raw disk block and need not contain a valid
272
* (formatted) disk page.
274
/* XXX should dig out of buffer descriptor */
275
#define BufferGetPageSize(buffer) \
277
AssertMacro(BufferIsValid(buffer)), \
283
* Returns the page associated with a buffer.
285
#define BufferGetPage(buffer) ((Page)BufferGetBlock(buffer))
288
* PageGetMaxOffsetNumber
289
* Returns the maximum offset number used by the given page.
290
* Since offset numbers are 1-based, this is also the number
291
* of items on the page.
293
* NOTE: if the page is not initialized (pd_lower == 0), we must
294
* return zero to ensure sane behavior. Accept double evaluation
295
* of the argument so that we can ensure this.
297
#define PageGetMaxOffsetNumber(page) \
298
(((PageHeader) (page))->pd_lower <= SizeOfPageHeaderData ? 0 : \
299
((((PageHeader) (page))->pd_lower - SizeOfPageHeaderData) \
300
/ sizeof(ItemIdData)))
302
#define PageGetLSN(page) \
303
(((PageHeader) (page))->pd_lsn)
304
#define PageSetLSN(page, lsn) \
305
(((PageHeader) (page))->pd_lsn = (lsn))
307
#define PageGetTLI(page) \
308
(((PageHeader) (page))->pd_tli)
309
#define PageSetTLI(page, tli) \
310
(((PageHeader) (page))->pd_tli = (tli))
312
/* ----------------------------------------------------------------
313
* extern declarations
314
* ----------------------------------------------------------------
317
extern void PageInit(Page page, Size pageSize, Size specialSize);
318
extern bool PageHeaderIsValid(PageHeader page);
319
extern OffsetNumber PageAddItem(Page page, Item item, Size size,
320
OffsetNumber offsetNumber, ItemIdFlags flags);
321
extern Page PageGetTempPage(Page page, Size specialSize);
322
extern void PageRestoreTempPage(Page tempPage, Page oldPage);
323
extern int PageRepairFragmentation(Page page, OffsetNumber *unused);
324
extern Size PageGetFreeSpace(Page page);
325
extern void PageIndexTupleDelete(Page page, OffsetNumber offset);
327
#endif /* BUFPAGE_H */