1 | /* |
2 | ** 2004 April 6 |
3 | ** |
4 | ** The author disclaims copyright to this source code. In place of |
5 | ** a legal notice, here is a blessing: |
6 | ** |
7 | ** May you do good and not evil. |
8 | ** May you find forgiveness for yourself and forgive others. |
9 | ** May you share freely, never taking more than you give. |
10 | ** |
11 | ************************************************************************* |
12 | ** This file implements an external (disk-based) database using BTrees. |
13 | ** For a detailed discussion of BTrees, refer to |
14 | ** |
15 | ** Donald E. Knuth, THE ART OF COMPUTER PROGRAMMING, Volume 3: |
16 | ** "Sorting And Searching", pages 473-480. Addison-Wesley |
17 | ** Publishing Company, Reading, Massachusetts. |
18 | ** |
19 | ** The basic idea is that each page of the file contains N database |
20 | ** entries and N+1 pointers to subpages. |
21 | ** |
22 | ** ---------------------------------------------------------------- |
23 | ** | Ptr(0) | Key(0) | Ptr(1) | Key(1) | ... | Key(N-1) | Ptr(N) | |
24 | ** ---------------------------------------------------------------- |
25 | ** |
26 | ** All of the keys on the page that Ptr(0) points to have values less |
27 | ** than Key(0). All of the keys on page Ptr(1) and its subpages have |
28 | ** values greater than Key(0) and less than Key(1). All of the keys |
29 | ** on Ptr(N) and its subpages have values greater than Key(N-1). And |
30 | ** so forth. |
31 | ** |
32 | ** Finding a particular key requires reading O(log(M)) pages from the |
33 | ** disk where M is the number of entries in the tree. |
34 | ** |
35 | ** In this implementation, a single file can hold one or more separate |
36 | ** BTrees. Each BTree is identified by the index of its root page. The |
37 | ** key and data for any entry are combined to form the "payload". A |
38 | ** fixed amount of payload can be carried directly on the database |
39 | ** page. If the payload is larger than the preset amount then surplus |
40 | ** bytes are stored on overflow pages. The payload for an entry |
41 | ** and the preceding pointer are combined to form a "Cell". Each |
42 | ** page has a small header which contains the Ptr(N) pointer and other |
43 | ** information such as the size of key and data. |
44 | ** |
45 | ** FORMAT DETAILS |
46 | ** |
47 | ** The file is divided into pages. The first page is called page 1, |
48 | ** the second is page 2, and so forth. A page number of zero indicates |
49 | ** "no such page". The page size can be any power of 2 between 512 and 65536. |
50 | ** Each page can be either a btree page, a freelist page, an overflow |
51 | ** page, or a pointer-map page. |
52 | ** |
53 | ** The first page is always a btree page. The first 100 bytes of the first |
54 | ** page contain a special header (the "file header") that describes the file. |
55 | ** The format of the file header is as follows: |
56 | ** |
57 | ** OFFSET SIZE DESCRIPTION |
58 | ** 0 16 Header string: "SQLite format 3\000" |
59 | ** 16 2 Page size in bytes. (1 means 65536) |
60 | ** 18 1 File format write version |
61 | ** 19 1 File format read version |
62 | ** 20 1 Bytes of unused space at the end of each page |
63 | ** 21 1 Max embedded payload fraction (must be 64) |
64 | ** 22 1 Min embedded payload fraction (must be 32) |
65 | ** 23 1 Min leaf payload fraction (must be 32) |
66 | ** 24 4 File change counter |
67 | ** 28 4 Reserved for future use |
68 | ** 32 4 First freelist page |
69 | ** 36 4 Number of freelist pages in the file |
70 | ** 40 60 15 4-byte meta values passed to higher layers |
71 | ** |
72 | ** 40 4 Schema cookie |
73 | ** 44 4 File format of schema layer |
74 | ** 48 4 Size of page cache |
75 | ** 52 4 Largest root-page (auto/incr_vacuum) |
76 | ** 56 4 1=UTF-8 2=UTF16le 3=UTF16be |
77 | ** 60 4 User version |
78 | ** 64 4 Incremental vacuum mode |
79 | ** 68 4 Application-ID |
80 | ** 72 20 unused |
81 | ** 92 4 The version-valid-for number |
82 | ** 96 4 SQLITE_VERSION_NUMBER |
83 | ** |
84 | ** All of the integer values are big-endian (most significant byte first). |
85 | ** |
86 | ** The file change counter is incremented when the database is changed |
87 | ** This counter allows other processes to know when the file has changed |
88 | ** and thus when they need to flush their cache. |
89 | ** |
90 | ** The max embedded payload fraction is the amount of the total usable |
91 | ** space in a page that can be consumed by a single cell for standard |
92 | ** B-tree (non-LEAFDATA) tables. A value of 255 means 100%. The default |
93 | ** is to limit the maximum cell size so that at least 4 cells will fit |
94 | ** on one page. Thus the default max embedded payload fraction is 64. |
95 | ** |
96 | ** If the payload for a cell is larger than the max payload, then extra |
97 | ** payload is spilled to overflow pages. Once an overflow page is allocated, |
98 | ** as many bytes as possible are moved into the overflow pages without letting |
99 | ** the cell size drop below the min embedded payload fraction. |
100 | ** |
101 | ** The min leaf payload fraction is like the min embedded payload fraction |
102 | ** except that it applies to leaf nodes in a LEAFDATA tree. The maximum |
103 | ** payload fraction for a LEAFDATA tree is always 100% (or 255) and it |
104 | ** not specified in the header. |
105 | ** |
106 | ** Each btree pages is divided into three sections: The header, the |
107 | ** cell pointer array, and the cell content area. Page 1 also has a 100-byte |
108 | ** file header that occurs before the page header. |
109 | ** |
110 | ** |----------------| |
111 | ** | file header | 100 bytes. Page 1 only. |
112 | ** |----------------| |
113 | ** | page header | 8 bytes for leaves. 12 bytes for interior nodes |
114 | ** |----------------| |
115 | ** | cell pointer | | 2 bytes per cell. Sorted order. |
116 | ** | array | | Grows downward |
117 | ** | | v |
118 | ** |----------------| |
119 | ** | unallocated | |
120 | ** | space | |
121 | ** |----------------| ^ Grows upwards |
122 | ** | cell content | | Arbitrary order interspersed with freeblocks. |
123 | ** | area | | and free space fragments. |
124 | ** |----------------| |
125 | ** |
126 | ** The page headers looks like this: |
127 | ** |
128 | ** OFFSET SIZE DESCRIPTION |
129 | ** 0 1 Flags. 1: intkey, 2: zerodata, 4: leafdata, 8: leaf |
130 | ** 1 2 byte offset to the first freeblock |
131 | ** 3 2 number of cells on this page |
132 | ** 5 2 first byte of the cell content area |
133 | ** 7 1 number of fragmented free bytes |
134 | ** 8 4 Right child (the Ptr(N) value). Omitted on leaves. |
135 | ** |
136 | ** The flags define the format of this btree page. The leaf flag means that |
137 | ** this page has no children. The zerodata flag means that this page carries |
138 | ** only keys and no data. The intkey flag means that the key is an integer |
139 | ** which is stored in the key size entry of the cell header rather than in |
140 | ** the payload area. |
141 | ** |
142 | ** The cell pointer array begins on the first byte after the page header. |
143 | ** The cell pointer array contains zero or more 2-byte numbers which are |
144 | ** offsets from the beginning of the page to the cell content in the cell |
145 | ** content area. The cell pointers occur in sorted order. The system strives |
146 | ** to keep free space after the last cell pointer so that new cells can |
147 | ** be easily added without having to defragment the page. |
148 | ** |
149 | ** Cell content is stored at the very end of the page and grows toward the |
150 | ** beginning of the page. |
151 | ** |
152 | ** Unused space within the cell content area is collected into a linked list of |
153 | ** freeblocks. Each freeblock is at least 4 bytes in size. The byte offset |
154 | ** to the first freeblock is given in the header. Freeblocks occur in |
155 | ** increasing order. Because a freeblock must be at least 4 bytes in size, |
156 | ** any group of 3 or fewer unused bytes in the cell content area cannot |
157 | ** exist on the freeblock chain. A group of 3 or fewer free bytes is called |
158 | ** a fragment. The total number of bytes in all fragments is recorded. |
159 | ** in the page header at offset 7. |
160 | ** |
161 | ** SIZE DESCRIPTION |
162 | ** 2 Byte offset of the next freeblock |
163 | ** 2 Bytes in this freeblock |
164 | ** |
165 | ** Cells are of variable length. Cells are stored in the cell content area at |
166 | ** the end of the page. Pointers to the cells are in the cell pointer array |
167 | ** that immediately follows the page header. Cells is not necessarily |
168 | ** contiguous or in order, but cell pointers are contiguous and in order. |
169 | ** |
170 | ** Cell content makes use of variable length integers. A variable |
171 | ** length integer is 1 to 9 bytes where the lower 7 bits of each |
172 | ** byte are used. The integer consists of all bytes that have bit 8 set and |
173 | ** the first byte with bit 8 clear. The most significant byte of the integer |
174 | ** appears first. A variable-length integer may not be more than 9 bytes long. |
175 | ** As a special case, all 8 bytes of the 9th byte are used as data. This |
176 | ** allows a 64-bit integer to be encoded in 9 bytes. |
177 | ** |
178 | ** 0x00 becomes 0x00000000 |
179 | ** 0x7f becomes 0x0000007f |
180 | ** 0x81 0x00 becomes 0x00000080 |
181 | ** 0x82 0x00 becomes 0x00000100 |
182 | ** 0x80 0x7f becomes 0x0000007f |
183 | ** 0x8a 0x91 0xd1 0xac 0x78 becomes 0x12345678 |
184 | ** 0x81 0x81 0x81 0x81 0x01 becomes 0x10204081 |
185 | ** |
186 | ** Variable length integers are used for rowids and to hold the number of |
187 | ** bytes of key and data in a btree cell. |
188 | ** |
189 | ** The content of a cell looks like this: |
190 | ** |
191 | ** SIZE DESCRIPTION |
192 | ** 4 Page number of the left child. Omitted if leaf flag is set. |
193 | ** var Number of bytes of data. Omitted if the zerodata flag is set. |
194 | ** var Number of bytes of key. Or the key itself if intkey flag is set. |
195 | ** * Payload |
196 | ** 4 First page of the overflow chain. Omitted if no overflow |
197 | ** |
198 | ** Overflow pages form a linked list. Each page except the last is completely |
199 | ** filled with data (pagesize - 4 bytes). The last page can have as little |
200 | ** as 1 byte of data. |
201 | ** |
202 | ** SIZE DESCRIPTION |
203 | ** 4 Page number of next overflow page |
204 | ** * Data |
205 | ** |
206 | ** Freelist pages come in two subtypes: trunk pages and leaf pages. The |
207 | ** file header points to the first in a linked list of trunk page. Each trunk |
208 | ** page points to multiple leaf pages. The content of a leaf page is |
209 | ** unspecified. A trunk page looks like this: |
210 | ** |
211 | ** SIZE DESCRIPTION |
212 | ** 4 Page number of next trunk page |
213 | ** 4 Number of leaf pointers on this page |
214 | ** * zero or more pages numbers of leaves |
215 | */ |
216 | #include "sqliteInt.h" |
217 | |
218 | |
219 | /* The following value is the maximum cell size assuming a maximum page |
220 | ** size give above. |
221 | */ |
222 | #define MX_CELL_SIZE(pBt) ((int)(pBt->pageSize-8)) |
223 | |
224 | /* The maximum number of cells on a single page of the database. This |
225 | ** assumes a minimum cell size of 6 bytes (4 bytes for the cell itself |
226 | ** plus 2 bytes for the index to the cell in the page header). Such |
227 | ** small cells will be rare, but they are possible. |
228 | */ |
229 | #define MX_CELL(pBt) ((pBt->pageSize-8)/6) |
230 | |
231 | /* Forward declarations */ |
232 | typedef struct MemPage MemPage; |
233 | typedef struct BtLock BtLock; |
234 | typedef struct CellInfo CellInfo; |
235 | |
236 | /* |
237 | ** This is a magic string that appears at the beginning of every |
238 | ** SQLite database in order to identify the file as a real database. |
239 | ** |
240 | ** You can change this value at compile-time by specifying a |
241 | ** -DSQLITE_FILE_HEADER="..." on the compiler command-line. The |
242 | ** header must be exactly 16 bytes including the zero-terminator so |
243 | ** the string itself should be 15 characters long. If you change |
244 | ** the header, then your custom library will not be able to read |
245 | ** databases generated by the standard tools and the standard tools |
246 | ** will not be able to read databases created by your custom library. |
247 | */ |
248 | #ifndef SQLITE_FILE_HEADER /* 123456789 123456 */ |
249 | # define "SQLite format 3" |
250 | #endif |
251 | |
252 | /* |
253 | ** Page type flags. An ORed combination of these flags appear as the |
254 | ** first byte of on-disk image of every BTree page. |
255 | */ |
256 | #define PTF_INTKEY 0x01 |
257 | #define PTF_ZERODATA 0x02 |
258 | #define PTF_LEAFDATA 0x04 |
259 | #define PTF_LEAF 0x08 |
260 | |
261 | /* |
262 | ** An instance of this object stores information about each a single database |
263 | ** page that has been loaded into memory. The information in this object |
264 | ** is derived from the raw on-disk page content. |
265 | ** |
266 | ** As each database page is loaded into memory, the pager allocats an |
267 | ** instance of this object and zeros the first 8 bytes. (This is the |
268 | ** "extra" information associated with each page of the pager.) |
269 | ** |
270 | ** Access to all fields of this structure is controlled by the mutex |
271 | ** stored in MemPage.pBt->mutex. |
272 | */ |
273 | struct MemPage { |
274 | u8 isInit; /* True if previously initialized. MUST BE FIRST! */ |
275 | u8 intKey; /* True if table b-trees. False for index b-trees */ |
276 | u8 intKeyLeaf; /* True if the leaf of an intKey table */ |
277 | Pgno pgno; /* Page number for this page */ |
278 | /* Only the first 8 bytes (above) are zeroed by pager.c when a new page |
279 | ** is allocated. All fields that follow must be initialized before use */ |
280 | u8 leaf; /* True if a leaf page */ |
281 | u8 hdrOffset; /* 100 for page 1. 0 otherwise */ |
282 | u8 childPtrSize; /* 0 if leaf==1. 4 if leaf==0 */ |
283 | u8 max1bytePayload; /* min(maxLocal,127) */ |
284 | u8 nOverflow; /* Number of overflow cell bodies in aCell[] */ |
285 | u16 maxLocal; /* Copy of BtShared.maxLocal or BtShared.maxLeaf */ |
286 | u16 minLocal; /* Copy of BtShared.minLocal or BtShared.minLeaf */ |
287 | u16 cellOffset; /* Index in aData of first cell pointer */ |
288 | int nFree; /* Number of free bytes on the page. -1 for unknown */ |
289 | u16 nCell; /* Number of cells on this page, local and ovfl */ |
290 | u16 maskPage; /* Mask for page offset */ |
291 | u16 aiOvfl[4]; /* Insert the i-th overflow cell before the aiOvfl-th |
292 | ** non-overflow cell */ |
293 | u8 *apOvfl[4]; /* Pointers to the body of overflow cells */ |
294 | BtShared *pBt; /* Pointer to BtShared that this page is part of */ |
295 | u8 *aData; /* Pointer to disk image of the page data */ |
296 | u8 *aDataEnd; /* One byte past the end of the entire page - not just |
297 | ** the usable space, the entire page. Used to prevent |
298 | ** corruption-induced buffer overflow. */ |
299 | u8 *aCellIdx; /* The cell index area */ |
300 | u8 *aDataOfst; /* Same as aData for leaves. aData+4 for interior */ |
301 | DbPage *pDbPage; /* Pager page handle */ |
302 | u16 (*xCellSize)(MemPage*,u8*); /* cellSizePtr method */ |
303 | void (*xParseCell)(MemPage*,u8*,CellInfo*); /* btreeParseCell method */ |
304 | }; |
305 | |
306 | /* |
307 | ** A linked list of the following structures is stored at BtShared.pLock. |
308 | ** Locks are added (or upgraded from READ_LOCK to WRITE_LOCK) when a cursor |
309 | ** is opened on the table with root page BtShared.iTable. Locks are removed |
310 | ** from this list when a transaction is committed or rolled back, or when |
311 | ** a btree handle is closed. |
312 | */ |
313 | struct BtLock { |
314 | Btree *pBtree; /* Btree handle holding this lock */ |
315 | Pgno iTable; /* Root page of table */ |
316 | u8 eLock; /* READ_LOCK or WRITE_LOCK */ |
317 | BtLock *pNext; /* Next in BtShared.pLock list */ |
318 | }; |
319 | |
320 | /* Candidate values for BtLock.eLock */ |
321 | #define READ_LOCK 1 |
322 | #define WRITE_LOCK 2 |
323 | |
324 | /* A Btree handle |
325 | ** |
326 | ** A database connection contains a pointer to an instance of |
327 | ** this object for every database file that it has open. This structure |
328 | ** is opaque to the database connection. The database connection cannot |
329 | ** see the internals of this structure and only deals with pointers to |
330 | ** this structure. |
331 | ** |
332 | ** For some database files, the same underlying database cache might be |
333 | ** shared between multiple connections. In that case, each connection |
334 | ** has it own instance of this object. But each instance of this object |
335 | ** points to the same BtShared object. The database cache and the |
336 | ** schema associated with the database file are all contained within |
337 | ** the BtShared object. |
338 | ** |
339 | ** All fields in this structure are accessed under sqlite3.mutex. |
340 | ** The pBt pointer itself may not be changed while there exists cursors |
341 | ** in the referenced BtShared that point back to this Btree since those |
342 | ** cursors have to go through this Btree to find their BtShared and |
343 | ** they often do so without holding sqlite3.mutex. |
344 | */ |
345 | struct Btree { |
346 | sqlite3 *db; /* The database connection holding this btree */ |
347 | BtShared *pBt; /* Sharable content of this btree */ |
348 | u8 inTrans; /* TRANS_NONE, TRANS_READ or TRANS_WRITE */ |
349 | u8 sharable; /* True if we can share pBt with another db */ |
350 | u8 locked; /* True if db currently has pBt locked */ |
351 | u8 hasIncrblobCur; /* True if there are one or more Incrblob cursors */ |
352 | int wantToLock; /* Number of nested calls to sqlite3BtreeEnter() */ |
353 | int nBackup; /* Number of backup operations reading this btree */ |
354 | u32 iBDataVersion; /* Combines with pBt->pPager->iDataVersion */ |
355 | Btree *pNext; /* List of other sharable Btrees from the same db */ |
356 | Btree *pPrev; /* Back pointer of the same list */ |
357 | #ifdef SQLITE_DEBUG |
358 | u64 nSeek; /* Calls to sqlite3BtreeMovetoUnpacked() */ |
359 | #endif |
360 | #ifndef SQLITE_OMIT_SHARED_CACHE |
361 | BtLock lock; /* Object used to lock page 1 */ |
362 | #endif |
363 | }; |
364 | |
365 | /* |
366 | ** Btree.inTrans may take one of the following values. |
367 | ** |
368 | ** If the shared-data extension is enabled, there may be multiple users |
369 | ** of the Btree structure. At most one of these may open a write transaction, |
370 | ** but any number may have active read transactions. |
371 | ** |
372 | ** These values must match SQLITE_TXN_NONE, SQLITE_TXN_READ, and |
373 | ** SQLITE_TXN_WRITE |
374 | */ |
375 | #define TRANS_NONE 0 |
376 | #define TRANS_READ 1 |
377 | #define TRANS_WRITE 2 |
378 | |
379 | #if TRANS_NONE!=SQLITE_TXN_NONE |
380 | # error wrong numeric code for no-transaction |
381 | #endif |
382 | #if TRANS_READ!=SQLITE_TXN_READ |
383 | # error wrong numeric code for read-transaction |
384 | #endif |
385 | #if TRANS_WRITE!=SQLITE_TXN_WRITE |
386 | # error wrong numeric code for write-transaction |
387 | #endif |
388 | |
389 | |
390 | /* |
391 | ** An instance of this object represents a single database file. |
392 | ** |
393 | ** A single database file can be in use at the same time by two |
394 | ** or more database connections. When two or more connections are |
395 | ** sharing the same database file, each connection has it own |
396 | ** private Btree object for the file and each of those Btrees points |
397 | ** to this one BtShared object. BtShared.nRef is the number of |
398 | ** connections currently sharing this database file. |
399 | ** |
400 | ** Fields in this structure are accessed under the BtShared.mutex |
401 | ** mutex, except for nRef and pNext which are accessed under the |
402 | ** global SQLITE_MUTEX_STATIC_MAIN mutex. The pPager field |
403 | ** may not be modified once it is initially set as long as nRef>0. |
404 | ** The pSchema field may be set once under BtShared.mutex and |
405 | ** thereafter is unchanged as long as nRef>0. |
406 | ** |
407 | ** isPending: |
408 | ** |
409 | ** If a BtShared client fails to obtain a write-lock on a database |
410 | ** table (because there exists one or more read-locks on the table), |
411 | ** the shared-cache enters 'pending-lock' state and isPending is |
412 | ** set to true. |
413 | ** |
414 | ** The shared-cache leaves the 'pending lock' state when either of |
415 | ** the following occur: |
416 | ** |
417 | ** 1) The current writer (BtShared.pWriter) concludes its transaction, OR |
418 | ** 2) The number of locks held by other connections drops to zero. |
419 | ** |
420 | ** while in the 'pending-lock' state, no connection may start a new |
421 | ** transaction. |
422 | ** |
423 | ** This feature is included to help prevent writer-starvation. |
424 | */ |
425 | struct BtShared { |
426 | Pager *; /* The page cache */ |
427 | sqlite3 *db; /* Database connection currently using this Btree */ |
428 | BtCursor *pCursor; /* A list of all open cursors */ |
429 | MemPage *pPage1; /* First page of the database */ |
430 | u8 openFlags; /* Flags to sqlite3BtreeOpen() */ |
431 | #ifndef SQLITE_OMIT_AUTOVACUUM |
432 | u8 autoVacuum; /* True if auto-vacuum is enabled */ |
433 | u8 incrVacuum; /* True if incr-vacuum is enabled */ |
434 | u8 bDoTruncate; /* True to truncate db on commit */ |
435 | #endif |
436 | u8 inTransaction; /* Transaction state */ |
437 | u8 max1bytePayload; /* Maximum first byte of cell for a 1-byte payload */ |
438 | u8 nReserveWanted; /* Desired number of extra bytes per page */ |
439 | u16 btsFlags; /* Boolean parameters. See BTS_* macros below */ |
440 | u16 maxLocal; /* Maximum local payload in non-LEAFDATA tables */ |
441 | u16 minLocal; /* Minimum local payload in non-LEAFDATA tables */ |
442 | u16 maxLeaf; /* Maximum local payload in a LEAFDATA table */ |
443 | u16 minLeaf; /* Minimum local payload in a LEAFDATA table */ |
444 | u32 pageSize; /* Total number of bytes on a page */ |
445 | u32 usableSize; /* Number of usable bytes on each page */ |
446 | int nTransaction; /* Number of open transactions (read + write) */ |
447 | u32 nPage; /* Number of pages in the database */ |
448 | void *pSchema; /* Pointer to space allocated by sqlite3BtreeSchema() */ |
449 | void (*xFreeSchema)(void*); /* Destructor for BtShared.pSchema */ |
450 | sqlite3_mutex *mutex; /* Non-recursive mutex required to access this object */ |
451 | Bitvec *pHasContent; /* Set of pages moved to free-list this transaction */ |
452 | #ifndef SQLITE_OMIT_SHARED_CACHE |
453 | int nRef; /* Number of references to this structure */ |
454 | BtShared *pNext; /* Next on a list of sharable BtShared structs */ |
455 | BtLock *pLock; /* List of locks held on this shared-btree struct */ |
456 | Btree *pWriter; /* Btree with currently open write transaction */ |
457 | #endif |
458 | u8 *pTmpSpace; /* Temp space sufficient to hold a single cell */ |
459 | int nPreformatSize; /* Size of last cell written by TransferRow() */ |
460 | }; |
461 | |
462 | /* |
463 | ** Allowed values for BtShared.btsFlags |
464 | */ |
465 | #define BTS_READ_ONLY 0x0001 /* Underlying file is readonly */ |
466 | #define BTS_PAGESIZE_FIXED 0x0002 /* Page size can no longer be changed */ |
467 | #define BTS_SECURE_DELETE 0x0004 /* PRAGMA secure_delete is enabled */ |
468 | #define BTS_OVERWRITE 0x0008 /* Overwrite deleted content with zeros */ |
469 | #define BTS_FAST_SECURE 0x000c /* Combination of the previous two */ |
470 | #define BTS_INITIALLY_EMPTY 0x0010 /* Database was empty at trans start */ |
471 | #define BTS_NO_WAL 0x0020 /* Do not open write-ahead-log files */ |
472 | #define BTS_EXCLUSIVE 0x0040 /* pWriter has an exclusive lock */ |
473 | #define BTS_PENDING 0x0080 /* Waiting for read-locks to clear */ |
474 | |
475 | /* |
476 | ** An instance of the following structure is used to hold information |
477 | ** about a cell. The parseCellPtr() function fills in this structure |
478 | ** based on information extract from the raw disk page. |
479 | */ |
480 | struct CellInfo { |
481 | i64 nKey; /* The key for INTKEY tables, or nPayload otherwise */ |
482 | u8 *pPayload; /* Pointer to the start of payload */ |
483 | u32 nPayload; /* Bytes of payload */ |
484 | u16 nLocal; /* Amount of payload held locally, not on overflow */ |
485 | u16 nSize; /* Size of the cell content on the main b-tree page */ |
486 | }; |
487 | |
488 | /* |
489 | ** Maximum depth of an SQLite B-Tree structure. Any B-Tree deeper than |
490 | ** this will be declared corrupt. This value is calculated based on a |
491 | ** maximum database size of 2^31 pages a minimum fanout of 2 for a |
492 | ** root-node and 3 for all other internal nodes. |
493 | ** |
494 | ** If a tree that appears to be taller than this is encountered, it is |
495 | ** assumed that the database is corrupt. |
496 | */ |
497 | #define BTCURSOR_MAX_DEPTH 20 |
498 | |
499 | /* |
500 | ** A cursor is a pointer to a particular entry within a particular |
501 | ** b-tree within a database file. |
502 | ** |
503 | ** The entry is identified by its MemPage and the index in |
504 | ** MemPage.aCell[] of the entry. |
505 | ** |
506 | ** A single database file can be shared by two more database connections, |
507 | ** but cursors cannot be shared. Each cursor is associated with a |
508 | ** particular database connection identified BtCursor.pBtree.db. |
509 | ** |
510 | ** Fields in this structure are accessed under the BtShared.mutex |
511 | ** found at self->pBt->mutex. |
512 | ** |
513 | ** skipNext meaning: |
514 | ** The meaning of skipNext depends on the value of eState: |
515 | ** |
516 | ** eState Meaning of skipNext |
517 | ** VALID skipNext is meaningless and is ignored |
518 | ** INVALID skipNext is meaningless and is ignored |
519 | ** SKIPNEXT sqlite3BtreeNext() is a no-op if skipNext>0 and |
520 | ** sqlite3BtreePrevious() is no-op if skipNext<0. |
521 | ** REQUIRESEEK restoreCursorPosition() restores the cursor to |
522 | ** eState=SKIPNEXT if skipNext!=0 |
523 | ** FAULT skipNext holds the cursor fault error code. |
524 | */ |
525 | struct BtCursor { |
526 | u8 eState; /* One of the CURSOR_XXX constants (see below) */ |
527 | u8 curFlags; /* zero or more BTCF_* flags defined below */ |
528 | u8 ; /* Flags to send to sqlite3PagerGet() */ |
529 | u8 hints; /* As configured by CursorSetHints() */ |
530 | int skipNext; /* Prev() is noop if negative. Next() is noop if positive. |
531 | ** Error code if eState==CURSOR_FAULT */ |
532 | Btree *pBtree; /* The Btree to which this cursor belongs */ |
533 | Pgno *aOverflow; /* Cache of overflow page locations */ |
534 | void *pKey; /* Saved key that was cursor last known position */ |
535 | /* All fields above are zeroed when the cursor is allocated. See |
536 | ** sqlite3BtreeCursorZero(). Fields that follow must be manually |
537 | ** initialized. */ |
538 | #define BTCURSOR_FIRST_UNINIT pBt /* Name of first uninitialized field */ |
539 | BtShared *pBt; /* The BtShared this cursor points to */ |
540 | BtCursor *pNext; /* Forms a linked list of all cursors */ |
541 | CellInfo info; /* A parse of the cell we are pointing at */ |
542 | i64 nKey; /* Size of pKey, or last integer key */ |
543 | Pgno pgnoRoot; /* The root page of this tree */ |
544 | i8 iPage; /* Index of current page in apPage */ |
545 | u8 curIntKey; /* Value of apPage[0]->intKey */ |
546 | u16 ix; /* Current index for apPage[iPage] */ |
547 | u16 aiIdx[BTCURSOR_MAX_DEPTH-1]; /* Current index in apPage[i] */ |
548 | struct KeyInfo *pKeyInfo; /* Arg passed to comparison function */ |
549 | MemPage *pPage; /* Current page */ |
550 | MemPage *apPage[BTCURSOR_MAX_DEPTH-1]; /* Stack of parents of current page */ |
551 | }; |
552 | |
553 | /* |
554 | ** Legal values for BtCursor.curFlags |
555 | */ |
556 | #define BTCF_WriteFlag 0x01 /* True if a write cursor */ |
557 | #define BTCF_ValidNKey 0x02 /* True if info.nKey is valid */ |
558 | #define BTCF_ValidOvfl 0x04 /* True if aOverflow is valid */ |
559 | #define BTCF_AtLast 0x08 /* Cursor is pointing ot the last entry */ |
560 | #define BTCF_Incrblob 0x10 /* True if an incremental I/O handle */ |
561 | #define BTCF_Multiple 0x20 /* Maybe another cursor on the same btree */ |
562 | #define BTCF_Pinned 0x40 /* Cursor is busy and cannot be moved */ |
563 | |
564 | /* |
565 | ** Potential values for BtCursor.eState. |
566 | ** |
567 | ** CURSOR_INVALID: |
568 | ** Cursor does not point to a valid entry. This can happen (for example) |
569 | ** because the table is empty or because BtreeCursorFirst() has not been |
570 | ** called. |
571 | ** |
572 | ** CURSOR_VALID: |
573 | ** Cursor points to a valid entry. getPayload() etc. may be called. |
574 | ** |
575 | ** CURSOR_SKIPNEXT: |
576 | ** Cursor is valid except that the Cursor.skipNext field is non-zero |
577 | ** indicating that the next sqlite3BtreeNext() or sqlite3BtreePrevious() |
578 | ** operation should be a no-op. |
579 | ** |
580 | ** CURSOR_REQUIRESEEK: |
581 | ** The table that this cursor was opened on still exists, but has been |
582 | ** modified since the cursor was last used. The cursor position is saved |
583 | ** in variables BtCursor.pKey and BtCursor.nKey. When a cursor is in |
584 | ** this state, restoreCursorPosition() can be called to attempt to |
585 | ** seek the cursor to the saved position. |
586 | ** |
587 | ** CURSOR_FAULT: |
588 | ** An unrecoverable error (an I/O error or a malloc failure) has occurred |
589 | ** on a different connection that shares the BtShared cache with this |
590 | ** cursor. The error has left the cache in an inconsistent state. |
591 | ** Do nothing else with this cursor. Any attempt to use the cursor |
592 | ** should return the error code stored in BtCursor.skipNext |
593 | */ |
594 | #define CURSOR_VALID 0 |
595 | #define CURSOR_INVALID 1 |
596 | #define CURSOR_SKIPNEXT 2 |
597 | #define CURSOR_REQUIRESEEK 3 |
598 | #define CURSOR_FAULT 4 |
599 | |
600 | /* |
601 | ** The database page the PENDING_BYTE occupies. This page is never used. |
602 | */ |
603 | #define PENDING_BYTE_PAGE(pBt) ((Pgno)((PENDING_BYTE/((pBt)->pageSize))+1)) |
604 | |
605 | /* |
606 | ** These macros define the location of the pointer-map entry for a |
607 | ** database page. The first argument to each is the number of usable |
608 | ** bytes on each page of the database (often 1024). The second is the |
609 | ** page number to look up in the pointer map. |
610 | ** |
611 | ** PTRMAP_PAGENO returns the database page number of the pointer-map |
612 | ** page that stores the required pointer. PTRMAP_PTROFFSET returns |
613 | ** the offset of the requested map entry. |
614 | ** |
615 | ** If the pgno argument passed to PTRMAP_PAGENO is a pointer-map page, |
616 | ** then pgno is returned. So (pgno==PTRMAP_PAGENO(pgsz, pgno)) can be |
617 | ** used to test if pgno is a pointer-map page. PTRMAP_ISPAGE implements |
618 | ** this test. |
619 | */ |
620 | #define PTRMAP_PAGENO(pBt, pgno) ptrmapPageno(pBt, pgno) |
621 | #define PTRMAP_PTROFFSET(pgptrmap, pgno) (5*(pgno-pgptrmap-1)) |
622 | #define PTRMAP_ISPAGE(pBt, pgno) (PTRMAP_PAGENO((pBt),(pgno))==(pgno)) |
623 | |
624 | /* |
625 | ** The pointer map is a lookup table that identifies the parent page for |
626 | ** each child page in the database file. The parent page is the page that |
627 | ** contains a pointer to the child. Every page in the database contains |
628 | ** 0 or 1 parent pages. (In this context 'database page' refers |
629 | ** to any page that is not part of the pointer map itself.) Each pointer map |
630 | ** entry consists of a single byte 'type' and a 4 byte parent page number. |
631 | ** The PTRMAP_XXX identifiers below are the valid types. |
632 | ** |
633 | ** The purpose of the pointer map is to facility moving pages from one |
634 | ** position in the file to another as part of autovacuum. When a page |
635 | ** is moved, the pointer in its parent must be updated to point to the |
636 | ** new location. The pointer map is used to locate the parent page quickly. |
637 | ** |
638 | ** PTRMAP_ROOTPAGE: The database page is a root-page. The page-number is not |
639 | ** used in this case. |
640 | ** |
641 | ** PTRMAP_FREEPAGE: The database page is an unused (free) page. The page-number |
642 | ** is not used in this case. |
643 | ** |
644 | ** PTRMAP_OVERFLOW1: The database page is the first page in a list of |
645 | ** overflow pages. The page number identifies the page that |
646 | ** contains the cell with a pointer to this overflow page. |
647 | ** |
648 | ** PTRMAP_OVERFLOW2: The database page is the second or later page in a list of |
649 | ** overflow pages. The page-number identifies the previous |
650 | ** page in the overflow page list. |
651 | ** |
652 | ** PTRMAP_BTREE: The database page is a non-root btree page. The page number |
653 | ** identifies the parent page in the btree. |
654 | */ |
655 | #define PTRMAP_ROOTPAGE 1 |
656 | #define PTRMAP_FREEPAGE 2 |
657 | #define PTRMAP_OVERFLOW1 3 |
658 | #define PTRMAP_OVERFLOW2 4 |
659 | #define PTRMAP_BTREE 5 |
660 | |
661 | /* A bunch of assert() statements to check the transaction state variables |
662 | ** of handle p (type Btree*) are internally consistent. |
663 | */ |
664 | #define btreeIntegrity(p) \ |
665 | assert( p->pBt->inTransaction!=TRANS_NONE || p->pBt->nTransaction==0 ); \ |
666 | assert( p->pBt->inTransaction>=p->inTrans ); |
667 | |
668 | |
669 | /* |
670 | ** The ISAUTOVACUUM macro is used within balance_nonroot() to determine |
671 | ** if the database supports auto-vacuum or not. Because it is used |
672 | ** within an expression that is an argument to another macro |
673 | ** (sqliteMallocRaw), it is not possible to use conditional compilation. |
674 | ** So, this macro is defined instead. |
675 | */ |
676 | #ifndef SQLITE_OMIT_AUTOVACUUM |
677 | #define ISAUTOVACUUM (pBt->autoVacuum) |
678 | #else |
679 | #define ISAUTOVACUUM 0 |
680 | #endif |
681 | |
682 | |
683 | /* |
684 | ** This structure is passed around through all the sanity checking routines |
685 | ** in order to keep track of some global state information. |
686 | ** |
687 | ** The aRef[] array is allocated so that there is 1 bit for each page in |
688 | ** the database. As the integrity-check proceeds, for each page used in |
689 | ** the database the corresponding bit is set. This allows integrity-check to |
690 | ** detect pages that are used twice and orphaned pages (both of which |
691 | ** indicate corruption). |
692 | */ |
693 | typedef struct IntegrityCk IntegrityCk; |
694 | struct IntegrityCk { |
695 | BtShared *pBt; /* The tree being checked out */ |
696 | Pager *; /* The associated pager. Also accessible by pBt->pPager */ |
697 | u8 *aPgRef; /* 1 bit per page in the db (see above) */ |
698 | Pgno nPage; /* Number of pages in the database */ |
699 | int mxErr; /* Stop accumulating errors when this reaches zero */ |
700 | int nErr; /* Number of messages written to zErrMsg so far */ |
701 | int bOomFault; /* A memory allocation error has occurred */ |
702 | const char *zPfx; /* Error message prefix */ |
703 | Pgno v1; /* Value for first %u substitution in zPfx */ |
704 | int v2; /* Value for second %d substitution in zPfx */ |
705 | StrAccum errMsg; /* Accumulate the error message text here */ |
706 | u32 *heap; /* Min-heap used for analyzing cell coverage */ |
707 | sqlite3 *db; /* Database connection running the check */ |
708 | }; |
709 | |
710 | /* |
711 | ** Routines to read or write a two- and four-byte big-endian integer values. |
712 | */ |
713 | #define get2byte(x) ((x)[0]<<8 | (x)[1]) |
714 | #define put2byte(p,v) ((p)[0] = (u8)((v)>>8), (p)[1] = (u8)(v)) |
715 | #define get4byte sqlite3Get4byte |
716 | #define put4byte sqlite3Put4byte |
717 | |
718 | /* |
719 | ** get2byteAligned(), unlike get2byte(), requires that its argument point to a |
720 | ** two-byte aligned address. get2bytea() is only used for accessing the |
721 | ** cell addresses in a btree header. |
722 | */ |
723 | #if SQLITE_BYTEORDER==4321 |
724 | # define get2byteAligned(x) (*(u16*)(x)) |
725 | #elif SQLITE_BYTEORDER==1234 && GCC_VERSION>=4008000 |
726 | # define get2byteAligned(x) __builtin_bswap16(*(u16*)(x)) |
727 | #elif SQLITE_BYTEORDER==1234 && MSVC_VERSION>=1300 |
728 | # define get2byteAligned(x) _byteswap_ushort(*(u16*)(x)) |
729 | #else |
730 | # define get2byteAligned(x) ((x)[0]<<8 | (x)[1]) |
731 | #endif |
732 | |