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bufpage.h
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1 /*-------------------------------------------------------------------------
2  *
3  * bufpage.h
4  * Standard POSTGRES buffer page definitions.
5  *
6  *
7  * Portions Copyright (c) 1996-2017, PostgreSQL Global Development Group
8  * Portions Copyright (c) 1994, Regents of the University of California
9  *
10  * src/include/storage/bufpage.h
11  *
12  *-------------------------------------------------------------------------
13  */
14 #ifndef BUFPAGE_H
15 #define BUFPAGE_H
16 
17 #include "access/xlogdefs.h"
18 #include "storage/block.h"
19 #include "storage/item.h"
20 #include "storage/off.h"
21 
22 /*
23  * A postgres disk page is an abstraction layered on top of a postgres
24  * disk block (which is simply a unit of i/o, see block.h).
25  *
26  * specifically, while a disk block can be unformatted, a postgres
27  * disk page is always a slotted page of the form:
28  *
29  * +----------------+---------------------------------+
30  * | PageHeaderData | linp1 linp2 linp3 ... |
31  * +-----------+----+---------------------------------+
32  * | ... linpN | |
33  * +-----------+--------------------------------------+
34  * | ^ pd_lower |
35  * | |
36  * | v pd_upper |
37  * +-------------+------------------------------------+
38  * | | tupleN ... |
39  * +-------------+------------------+-----------------+
40  * | ... tuple3 tuple2 tuple1 | "special space" |
41  * +--------------------------------+-----------------+
42  * ^ pd_special
43  *
44  * a page is full when nothing can be added between pd_lower and
45  * pd_upper.
46  *
47  * all blocks written out by an access method must be disk pages.
48  *
49  * EXCEPTIONS:
50  *
51  * obviously, a page is not formatted before it is initialized by
52  * a call to PageInit.
53  *
54  * NOTES:
55  *
56  * linp1..N form an ItemId array. ItemPointers point into this array
57  * rather than pointing directly to a tuple. Note that OffsetNumbers
58  * conventionally start at 1, not 0.
59  *
60  * tuple1..N are added "backwards" on the page. because a tuple's
61  * ItemPointer points to its ItemId entry rather than its actual
62  * byte-offset position, tuples can be physically shuffled on a page
63  * whenever the need arises.
64  *
65  * AM-generic per-page information is kept in PageHeaderData.
66  *
67  * AM-specific per-page data (if any) is kept in the area marked "special
68  * space"; each AM has an "opaque" structure defined somewhere that is
69  * stored as the page trailer. an access method should always
70  * initialize its pages with PageInit and then set its own opaque
71  * fields.
72  */
73 
74 typedef Pointer Page;
75 
76 
77 /*
78  * location (byte offset) within a page.
79  *
80  * note that this is actually limited to 2^15 because we have limited
81  * ItemIdData.lp_off and ItemIdData.lp_len to 15 bits (see itemid.h).
82  */
84 
85 
86 /*
87  * For historical reasons, the 64-bit LSN value is stored as two 32-bit
88  * values.
89  */
90 typedef struct
91 {
92  uint32 xlogid; /* high bits */
93  uint32 xrecoff; /* low bits */
95 
96 #define PageXLogRecPtrGet(val) \
97  ((uint64) (val).xlogid << 32 | (val).xrecoff)
98 #define PageXLogRecPtrSet(ptr, lsn) \
99  ((ptr).xlogid = (uint32) ((lsn) >> 32), (ptr).xrecoff = (uint32) (lsn))
100 
101 /*
102  * disk page organization
103  *
104  * space management information generic to any page
105  *
106  * pd_lsn - identifies xlog record for last change to this page.
107  * pd_checksum - page checksum, if set.
108  * pd_flags - flag bits.
109  * pd_lower - offset to start of free space.
110  * pd_upper - offset to end of free space.
111  * pd_special - offset to start of special space.
112  * pd_pagesize_version - size in bytes and page layout version number.
113  * pd_prune_xid - oldest XID among potentially prunable tuples on page.
114  *
115  * The LSN is used by the buffer manager to enforce the basic rule of WAL:
116  * "thou shalt write xlog before data". A dirty buffer cannot be dumped
117  * to disk until xlog has been flushed at least as far as the page's LSN.
118  *
119  * pd_checksum stores the page checksum, if it has been set for this page;
120  * zero is a valid value for a checksum. If a checksum is not in use then
121  * we leave the field unset. This will typically mean the field is zero
122  * though non-zero values may also be present if databases have been
123  * pg_upgraded from releases prior to 9.3, when the same byte offset was
124  * used to store the current timelineid when the page was last updated.
125  * Note that there is no indication on a page as to whether the checksum
126  * is valid or not, a deliberate design choice which avoids the problem
127  * of relying on the page contents to decide whether to verify it. Hence
128  * there are no flag bits relating to checksums.
129  *
130  * pd_prune_xid is a hint field that helps determine whether pruning will be
131  * useful. It is currently unused in index pages.
132  *
133  * The page version number and page size are packed together into a single
134  * uint16 field. This is for historical reasons: before PostgreSQL 7.3,
135  * there was no concept of a page version number, and doing it this way
136  * lets us pretend that pre-7.3 databases have page version number zero.
137  * We constrain page sizes to be multiples of 256, leaving the low eight
138  * bits available for a version number.
139  *
140  * Minimum possible page size is perhaps 64B to fit page header, opaque space
141  * and a minimal tuple; of course, in reality you want it much bigger, so
142  * the constraint on pagesize mod 256 is not an important restriction.
143  * On the high end, we can only support pages up to 32KB because lp_off/lp_len
144  * are 15 bits.
145  */
146 
147 typedef struct PageHeaderData
148 {
149  /* XXX LSN is member of *any* block, not only page-organized ones */
150  PageXLogRecPtr pd_lsn; /* LSN: next byte after last byte of xlog
151  * record for last change to this page */
152  uint16 pd_checksum; /* checksum */
153  uint16 pd_flags; /* flag bits, see below */
154  LocationIndex pd_lower; /* offset to start of free space */
155  LocationIndex pd_upper; /* offset to end of free space */
156  LocationIndex pd_special; /* offset to start of special space */
158  TransactionId pd_prune_xid; /* oldest prunable XID, or zero if none */
159  ItemIdData pd_linp[FLEXIBLE_ARRAY_MEMBER]; /* line pointer array */
161 
163 
164 /*
165  * pd_flags contains the following flag bits. Undefined bits are initialized
166  * to zero and may be used in the future.
167  *
168  * PD_HAS_FREE_LINES is set if there are any LP_UNUSED line pointers before
169  * pd_lower. This should be considered a hint rather than the truth, since
170  * changes to it are not WAL-logged.
171  *
172  * PD_PAGE_FULL is set if an UPDATE doesn't find enough free space in the
173  * page for its new tuple version; this suggests that a prune is needed.
174  * Again, this is just a hint.
175  */
176 #define PD_HAS_FREE_LINES 0x0001 /* are there any unused line pointers? */
177 #define PD_PAGE_FULL 0x0002 /* not enough free space for new tuple? */
178 #define PD_ALL_VISIBLE 0x0004 /* all tuples on page are visible to
179  * everyone */
180 
181 #define PD_VALID_FLAG_BITS 0x0007 /* OR of all valid pd_flags bits */
182 
183 /*
184  * Page layout version number 0 is for pre-7.3 Postgres releases.
185  * Releases 7.3 and 7.4 use 1, denoting a new HeapTupleHeader layout.
186  * Release 8.0 uses 2; it changed the HeapTupleHeader layout again.
187  * Release 8.1 uses 3; it redefined HeapTupleHeader infomask bits.
188  * Release 8.3 uses 4; it changed the HeapTupleHeader layout again, and
189  * added the pd_flags field (by stealing some bits from pd_tli),
190  * as well as adding the pd_prune_xid field (which enlarges the header).
191  *
192  * As of Release 9.3, the checksum version must also be considered when
193  * handling pages.
194  */
195 #define PG_PAGE_LAYOUT_VERSION 4
196 #define PG_DATA_CHECKSUM_VERSION 1
197 
198 /* ----------------------------------------------------------------
199  * page support macros
200  * ----------------------------------------------------------------
201  */
202 
203 /*
204  * PageIsValid
205  * True iff page is valid.
206  */
207 #define PageIsValid(page) PointerIsValid(page)
208 
209 /*
210  * line pointer(s) do not count as part of header
211  */
212 #define SizeOfPageHeaderData (offsetof(PageHeaderData, pd_linp))
213 
214 /*
215  * PageIsEmpty
216  * returns true iff no itemid has been allocated on the page
217  */
218 #define PageIsEmpty(page) \
219  (((PageHeader) (page))->pd_lower <= SizeOfPageHeaderData)
220 
221 /*
222  * PageIsNew
223  * returns true iff page has not been initialized (by PageInit)
224  */
225 #define PageIsNew(page) (((PageHeader) (page))->pd_upper == 0)
226 
227 /*
228  * PageGetItemId
229  * Returns an item identifier of a page.
230  */
231 #define PageGetItemId(page, offsetNumber) \
232  ((ItemId) (&((PageHeader) (page))->pd_linp[(offsetNumber) - 1]))
233 
234 /*
235  * PageGetContents
236  * To be used in case the page does not contain item pointers.
237  *
238  * Note: prior to 8.3 this was not guaranteed to yield a MAXALIGN'd result.
239  * Now it is. Beware of old code that might think the offset to the contents
240  * is just SizeOfPageHeaderData rather than MAXALIGN(SizeOfPageHeaderData).
241  */
242 #define PageGetContents(page) \
243  ((char *) (page) + MAXALIGN(SizeOfPageHeaderData))
244 
245 /* ----------------
246  * macros to access page size info
247  * ----------------
248  */
249 
250 /*
251  * PageSizeIsValid
252  * True iff the page size is valid.
253  */
254 #define PageSizeIsValid(pageSize) ((pageSize) == BLCKSZ)
255 
256 /*
257  * PageGetPageSize
258  * Returns the page size of a page.
259  *
260  * this can only be called on a formatted page (unlike
261  * BufferGetPageSize, which can be called on an unformatted page).
262  * however, it can be called on a page that is not stored in a buffer.
263  */
264 #define PageGetPageSize(page) \
265  ((Size) (((PageHeader) (page))->pd_pagesize_version & (uint16) 0xFF00))
266 
267 /*
268  * PageGetPageLayoutVersion
269  * Returns the page layout version of a page.
270  */
271 #define PageGetPageLayoutVersion(page) \
272  (((PageHeader) (page))->pd_pagesize_version & 0x00FF)
273 
274 /*
275  * PageSetPageSizeAndVersion
276  * Sets the page size and page layout version number of a page.
277  *
278  * We could support setting these two values separately, but there's
279  * no real need for it at the moment.
280  */
281 #define PageSetPageSizeAndVersion(page, size, version) \
282 ( \
283  AssertMacro(((size) & 0xFF00) == (size)), \
284  AssertMacro(((version) & 0x00FF) == (version)), \
285  ((PageHeader) (page))->pd_pagesize_version = (size) | (version) \
286 )
287 
288 /* ----------------
289  * page special data macros
290  * ----------------
291  */
292 /*
293  * PageGetSpecialSize
294  * Returns size of special space on a page.
295  */
296 #define PageGetSpecialSize(page) \
297  ((uint16) (PageGetPageSize(page) - ((PageHeader)(page))->pd_special))
298 
299 /*
300  * Using assertions, validate that the page special pointer is OK.
301  *
302  * This is intended to catch use of the pointer before page initialization.
303  * It is implemented as a function due to the limitations of the MSVC
304  * compiler, which choked on doing all these tests within another macro. We
305  * return true so that MacroAssert() can be used while still getting the
306  * specifics from the macro failure within this function.
307  */
308 static inline bool
310 {
311  Assert(PageIsValid(page));
312  Assert(((PageHeader) (page))->pd_special <= BLCKSZ);
313  Assert(((PageHeader) (page))->pd_special >= SizeOfPageHeaderData);
314 
315  return true;
316 }
317 
318 /*
319  * PageGetSpecialPointer
320  * Returns pointer to special space on a page.
321  */
322 #define PageGetSpecialPointer(page) \
323 ( \
324  AssertMacro(PageValidateSpecialPointer(page)), \
325  (char *) ((char *) (page) + ((PageHeader) (page))->pd_special) \
326 )
327 
328 /*
329  * PageGetItem
330  * Retrieves an item on the given page.
331  *
332  * Note:
333  * This does not change the status of any of the resources passed.
334  * The semantics may change in the future.
335  */
336 #define PageGetItem(page, itemId) \
337 ( \
338  AssertMacro(PageIsValid(page)), \
339  AssertMacro(ItemIdHasStorage(itemId)), \
340  (Item)(((char *)(page)) + ItemIdGetOffset(itemId)) \
341 )
342 
343 /*
344  * PageGetMaxOffsetNumber
345  * Returns the maximum offset number used by the given page.
346  * Since offset numbers are 1-based, this is also the number
347  * of items on the page.
348  *
349  * NOTE: if the page is not initialized (pd_lower == 0), we must
350  * return zero to ensure sane behavior. Accept double evaluation
351  * of the argument so that we can ensure this.
352  */
353 #define PageGetMaxOffsetNumber(page) \
354  (((PageHeader) (page))->pd_lower <= SizeOfPageHeaderData ? 0 : \
355  ((((PageHeader) (page))->pd_lower - SizeOfPageHeaderData) \
356  / sizeof(ItemIdData)))
357 
358 /*
359  * Additional macros for access to page headers. (Beware multiple evaluation
360  * of the arguments!)
361  */
362 #define PageGetLSN(page) \
363  PageXLogRecPtrGet(((PageHeader) (page))->pd_lsn)
364 #define PageSetLSN(page, lsn) \
365  PageXLogRecPtrSet(((PageHeader) (page))->pd_lsn, lsn)
366 
367 #define PageHasFreeLinePointers(page) \
368  (((PageHeader) (page))->pd_flags & PD_HAS_FREE_LINES)
369 #define PageSetHasFreeLinePointers(page) \
370  (((PageHeader) (page))->pd_flags |= PD_HAS_FREE_LINES)
371 #define PageClearHasFreeLinePointers(page) \
372  (((PageHeader) (page))->pd_flags &= ~PD_HAS_FREE_LINES)
373 
374 #define PageIsFull(page) \
375  (((PageHeader) (page))->pd_flags & PD_PAGE_FULL)
376 #define PageSetFull(page) \
377  (((PageHeader) (page))->pd_flags |= PD_PAGE_FULL)
378 #define PageClearFull(page) \
379  (((PageHeader) (page))->pd_flags &= ~PD_PAGE_FULL)
380 
381 #define PageIsAllVisible(page) \
382  (((PageHeader) (page))->pd_flags & PD_ALL_VISIBLE)
383 #define PageSetAllVisible(page) \
384  (((PageHeader) (page))->pd_flags |= PD_ALL_VISIBLE)
385 #define PageClearAllVisible(page) \
386  (((PageHeader) (page))->pd_flags &= ~PD_ALL_VISIBLE)
387 
388 #define PageIsPrunable(page, oldestxmin) \
389 ( \
390  AssertMacro(TransactionIdIsNormal(oldestxmin)), \
391  TransactionIdIsValid(((PageHeader) (page))->pd_prune_xid) && \
392  TransactionIdPrecedes(((PageHeader) (page))->pd_prune_xid, oldestxmin) \
393 )
394 #define PageSetPrunable(page, xid) \
395 do { \
396  Assert(TransactionIdIsNormal(xid)); \
397  if (!TransactionIdIsValid(((PageHeader) (page))->pd_prune_xid) || \
398  TransactionIdPrecedes(xid, ((PageHeader) (page))->pd_prune_xid)) \
399  ((PageHeader) (page))->pd_prune_xid = (xid); \
400 } while (0)
401 #define PageClearPrunable(page) \
402  (((PageHeader) (page))->pd_prune_xid = InvalidTransactionId)
403 
404 
405 /* ----------------------------------------------------------------
406  * extern declarations
407  * ----------------------------------------------------------------
408  */
409 #define PAI_OVERWRITE (1 << 0)
410 #define PAI_IS_HEAP (1 << 1)
411 
412 #define PageAddItem(page, item, size, offsetNumber, overwrite, is_heap) \
413  PageAddItemExtended(page, item, size, offsetNumber, \
414  ((overwrite) ? PAI_OVERWRITE : 0) | \
415  ((is_heap) ? PAI_IS_HEAP : 0))
416 
417 extern void PageInit(Page page, Size pageSize, Size specialSize);
418 extern bool PageIsVerified(Page page, BlockNumber blkno);
419 extern OffsetNumber PageAddItemExtended(Page page, Item item, Size size,
420  OffsetNumber offsetNumber, int flags);
421 extern Page PageGetTempPage(Page page);
422 extern Page PageGetTempPageCopy(Page page);
424 extern void PageRestoreTempPage(Page tempPage, Page oldPage);
425 extern void PageRepairFragmentation(Page page);
426 extern Size PageGetFreeSpace(Page page);
427 extern Size PageGetFreeSpaceForMultipleTuples(Page page, int ntups);
428 extern Size PageGetExactFreeSpace(Page page);
429 extern Size PageGetHeapFreeSpace(Page page);
430 extern void PageIndexTupleDelete(Page page, OffsetNumber offset);
431 extern void PageIndexMultiDelete(Page page, OffsetNumber *itemnos, int nitems);
432 extern void PageIndexTupleDeleteNoCompact(Page page, OffsetNumber offset);
433 extern bool PageIndexTupleOverwrite(Page page, OffsetNumber offnum,
434  Item newtup, Size newsize);
435 extern char *PageSetChecksumCopy(Page page, BlockNumber blkno);
436 extern void PageSetChecksumInplace(Page page, BlockNumber blkno);
437 
438 #endif /* BUFPAGE_H */
Size PageGetFreeSpaceForMultipleTuples(Page page, int ntups)
Definition: bufpage.c:609
void PageIndexTupleDelete(Page page, OffsetNumber offset)
Definition: bufpage.c:727
uint32 TransactionId
Definition: c.h:391
uint16 pd_flags
Definition: bufpage.h:153
void PageIndexMultiDelete(Page page, OffsetNumber *itemnos, int nitems)
Definition: bufpage.c:836
void PageSetChecksumInplace(Page page, BlockNumber blkno)
Definition: bufpage.c:1199
Pointer Item
Definition: item.h:17
static bool PageValidateSpecialPointer(Page page)
Definition: bufpage.h:309
void PageRepairFragmentation(Page page)
Definition: bufpage.c:479
uint32 BlockNumber
Definition: block.h:31
uint32 xlogid
Definition: bufpage.h:92
#define PageIsValid(page)
Definition: bufpage.h:207
#define SizeOfPageHeaderData
Definition: bufpage.h:212
uint16 OffsetNumber
Definition: off.h:24
uint16 pd_checksum
Definition: bufpage.h:152
OffsetNumber PageAddItemExtended(Page page, Item item, Size size, OffsetNumber offsetNumber, int flags)
Definition: bufpage.c:190
unsigned short uint16
Definition: c.h:257
Page PageGetTempPage(Page page)
Definition: bufpage.c:348
char * Pointer
Definition: c.h:235
Size PageGetExactFreeSpace(Page page)
Definition: bufpage.c:633
void PageInit(Page page, Size pageSize, Size specialSize)
Definition: bufpage.c:41
Page PageGetTempPageCopy(Page page)
Definition: bufpage.c:365
unsigned int uint32
Definition: c.h:258
Size PageGetFreeSpace(Page page)
Definition: bufpage.c:582
uint16 pd_pagesize_version
Definition: bufpage.h:157
Page PageGetTempPageCopySpecial(Page page)
Definition: bufpage.c:385
LocationIndex pd_special
Definition: bufpage.h:156
uint16 LocationIndex
Definition: bufpage.h:83
void PageRestoreTempPage(Page tempPage, Page oldPage)
Definition: bufpage.c:407
bool PageIsVerified(Page page, BlockNumber blkno)
Definition: bufpage.c:81
struct PageHeaderData PageHeaderData
PageHeaderData * PageHeader
Definition: bufpage.h:162
#define Assert(condition)
Definition: c.h:681
void PageIndexTupleDeleteNoCompact(Page page, OffsetNumber offset)
Definition: bufpage.c:958
TransactionId pd_prune_xid
Definition: bufpage.h:158
size_t Size
Definition: c.h:350
char * PageSetChecksumCopy(Page page, BlockNumber blkno)
Definition: bufpage.c:1170
Size PageGetHeapFreeSpace(Page page)
Definition: bufpage.c:666
ItemIdData pd_linp[FLEXIBLE_ARRAY_MEMBER]
Definition: bufpage.h:159
bool PageIndexTupleOverwrite(Page page, OffsetNumber offnum, Item newtup, Size newsize)
Definition: bufpage.c:1066
uint32 xrecoff
Definition: bufpage.h:93
LocationIndex pd_upper
Definition: bufpage.h:155
PageXLogRecPtr pd_lsn
Definition: bufpage.h:150
Pointer Page
Definition: bufpage.h:74
LocationIndex pd_lower
Definition: bufpage.h:154