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 a 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 a 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; 234 235 /* 236 ** This is a magic string that appears at the beginning of every 237 ** SQLite database in order to identify the file as a real database. 238 ** 239 ** You can change this value at compile-time by specifying a 240 ** -DSQLITE_FILE_HEADER="..." on the compiler command-line. The 241 ** header must be exactly 16 bytes including the zero-terminator so 242 ** the string itself should be 15 characters long. If you change 243 ** the header, then your custom library will not be able to read 244 ** databases generated by the standard tools and the standard tools 245 ** will not be able to read databases created by your custom library. 246 */ 247 #ifndef SQLITE_FILE_HEADER /* 123456789 123456 */ 248 # define SQLITE_FILE_HEADER "SQLite format 3" 249 #endif 250 251 /* 252 ** Page type flags. An ORed combination of these flags appear as the 253 ** first byte of on-disk image of every BTree page. 254 */ 255 #define PTF_INTKEY 0x01 256 #define PTF_ZERODATA 0x02 257 #define PTF_LEAFDATA 0x04 258 #define PTF_LEAF 0x08 259 260 /* 261 ** As each page of the file is loaded into memory, an instance of the following 262 ** structure is appended and initialized to zero. This structure stores 263 ** information about the page that is decoded from the raw file page. 264 ** 265 ** The pParent field points back to the parent page. This allows us to 266 ** walk up the BTree from any leaf to the root. Care must be taken to 267 ** unref() the parent page pointer when this page is no longer referenced. 268 ** The pageDestructor() routine handles that chore. 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 nOverflow; /* Number of overflow cell bodies in aCell[] */ 276 u8 intKey; /* True if intkey flag is set */ 277 u8 leaf; /* True if leaf flag is set */ 278 u8 hasData; /* True if this page stores data */ 279 u8 hdrOffset; /* 100 for page 1. 0 otherwise */ 280 u8 childPtrSize; /* 0 if leaf==1. 4 if leaf==0 */ 281 u8 max1bytePayload; /* min(maxLocal,127) */ 282 u16 maxLocal; /* Copy of BtShared.maxLocal or BtShared.maxLeaf */ 283 u16 minLocal; /* Copy of BtShared.minLocal or BtShared.minLeaf */ 284 u16 cellOffset; /* Index in aData of first cell pointer */ 285 u16 nFree; /* Number of free bytes on the page */ 286 u16 nCell; /* Number of cells on this page, local and ovfl */ 287 u16 maskPage; /* Mask for page offset */ 288 u16 aiOvfl[5]; /* Insert the i-th overflow cell before the aiOvfl-th 289 ** non-overflow cell */ 290 u8 *apOvfl[5]; /* Pointers to the body of overflow cells */ 291 BtShared *pBt; /* Pointer to BtShared that this page is part of */ 292 u8 *aData; /* Pointer to disk image of the page data */ 293 u8 *aDataEnd; /* One byte past the end of usable data */ 294 u8 *aCellIdx; /* The cell index area */ 295 DbPage *pDbPage; /* Pager page handle */ 296 Pgno pgno; /* Page number for this page */ 297 }; 298 299 /* 300 ** The in-memory image of a disk page has the auxiliary information appended 301 ** to the end. EXTRA_SIZE is the number of bytes of space needed to hold 302 ** that extra information. 303 */ 304 #define EXTRA_SIZE sizeof(MemPage) 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 int wantToLock; /* Number of nested calls to sqlite3BtreeEnter() */ 352 int nBackup; /* Number of backup operations reading this btree */ 353 Btree *pNext; /* List of other sharable Btrees from the same db */ 354 Btree *pPrev; /* Back pointer of the same list */ 355 #ifndef SQLITE_OMIT_SHARED_CACHE 356 BtLock lock; /* Object used to lock page 1 */ 357 #endif 358 }; 359 360 /* 361 ** Btree.inTrans may take one of the following values. 362 ** 363 ** If the shared-data extension is enabled, there may be multiple users 364 ** of the Btree structure. At most one of these may open a write transaction, 365 ** but any number may have active read transactions. 366 */ 367 #define TRANS_NONE 0 368 #define TRANS_READ 1 369 #define TRANS_WRITE 2 370 371 /* 372 ** An instance of this object represents a single database file. 373 ** 374 ** A single database file can be in use at the same time by two 375 ** or more database connections. When two or more connections are 376 ** sharing the same database file, each connection has it own 377 ** private Btree object for the file and each of those Btrees points 378 ** to this one BtShared object. BtShared.nRef is the number of 379 ** connections currently sharing this database file. 380 ** 381 ** Fields in this structure are accessed under the BtShared.mutex 382 ** mutex, except for nRef and pNext which are accessed under the 383 ** global SQLITE_MUTEX_STATIC_MASTER mutex. The pPager field 384 ** may not be modified once it is initially set as long as nRef>0. 385 ** The pSchema field may be set once under BtShared.mutex and 386 ** thereafter is unchanged as long as nRef>0. 387 ** 388 ** isPending: 389 ** 390 ** If a BtShared client fails to obtain a write-lock on a database 391 ** table (because there exists one or more read-locks on the table), 392 ** the shared-cache enters 'pending-lock' state and isPending is 393 ** set to true. 394 ** 395 ** The shared-cache leaves the 'pending lock' state when either of 396 ** the following occur: 397 ** 398 ** 1) The current writer (BtShared.pWriter) concludes its transaction, OR 399 ** 2) The number of locks held by other connections drops to zero. 400 ** 401 ** while in the 'pending-lock' state, no connection may start a new 402 ** transaction. 403 ** 404 ** This feature is included to help prevent writer-starvation. 405 */ 406 struct BtShared { 407 Pager *pPager; /* The page cache */ 408 sqlite3 *db; /* Database connection currently using this Btree */ 409 BtCursor *pCursor; /* A list of all open cursors */ 410 MemPage *pPage1; /* First page of the database */ 411 u8 openFlags; /* Flags to sqlite3BtreeOpen() */ 412 #ifndef SQLITE_OMIT_AUTOVACUUM 413 u8 autoVacuum; /* True if auto-vacuum is enabled */ 414 u8 incrVacuum; /* True if incr-vacuum is enabled */ 415 u8 bDoTruncate; /* True to truncate db on commit */ 416 #endif 417 u8 inTransaction; /* Transaction state */ 418 u8 max1bytePayload; /* Maximum first byte of cell for a 1-byte payload */ 419 u16 btsFlags; /* Boolean parameters. See BTS_* macros below */ 420 u16 maxLocal; /* Maximum local payload in non-LEAFDATA tables */ 421 u16 minLocal; /* Minimum local payload in non-LEAFDATA tables */ 422 u16 maxLeaf; /* Maximum local payload in a LEAFDATA table */ 423 u16 minLeaf; /* Minimum local payload in a LEAFDATA table */ 424 u32 pageSize; /* Total number of bytes on a page */ 425 u32 usableSize; /* Number of usable bytes on each page */ 426 int nTransaction; /* Number of open transactions (read + write) */ 427 u32 nPage; /* Number of pages in the database */ 428 void *pSchema; /* Pointer to space allocated by sqlite3BtreeSchema() */ 429 void (*xFreeSchema)(void*); /* Destructor for BtShared.pSchema */ 430 sqlite3_mutex *mutex; /* Non-recursive mutex required to access this object */ 431 Bitvec *pHasContent; /* Set of pages moved to free-list this transaction */ 432 #ifndef SQLITE_OMIT_SHARED_CACHE 433 int nRef; /* Number of references to this structure */ 434 BtShared *pNext; /* Next on a list of sharable BtShared structs */ 435 BtLock *pLock; /* List of locks held on this shared-btree struct */ 436 Btree *pWriter; /* Btree with currently open write transaction */ 437 #endif 438 u8 *pTmpSpace; /* BtShared.pageSize bytes of space for tmp use */ 439 }; 440 441 /* 442 ** Allowed values for BtShared.btsFlags 443 */ 444 #define BTS_READ_ONLY 0x0001 /* Underlying file is readonly */ 445 #define BTS_PAGESIZE_FIXED 0x0002 /* Page size can no longer be changed */ 446 #define BTS_SECURE_DELETE 0x0004 /* PRAGMA secure_delete is enabled */ 447 #define BTS_INITIALLY_EMPTY 0x0008 /* Database was empty at trans start */ 448 #define BTS_NO_WAL 0x0010 /* Do not open write-ahead-log files */ 449 #define BTS_EXCLUSIVE 0x0020 /* pWriter has an exclusive lock */ 450 #define BTS_PENDING 0x0040 /* Waiting for read-locks to clear */ 451 452 /* 453 ** An instance of the following structure is used to hold information 454 ** about a cell. The parseCellPtr() function fills in this structure 455 ** based on information extract from the raw disk page. 456 */ 457 typedef struct CellInfo CellInfo; 458 struct CellInfo { 459 i64 nKey; /* The key for INTKEY tables, or number of bytes in key */ 460 u8 *pCell; /* Pointer to the start of cell content */ 461 u32 nData; /* Number of bytes of data */ 462 u32 nPayload; /* Total amount of payload */ 463 u16 nHeader; /* Size of the cell content header in bytes */ 464 u16 nLocal; /* Amount of payload held locally */ 465 u16 iOverflow; /* Offset to overflow page number. Zero if no overflow */ 466 u16 nSize; /* Size of the cell content on the main b-tree page */ 467 }; 468 469 /* 470 ** Maximum depth of an SQLite B-Tree structure. Any B-Tree deeper than 471 ** this will be declared corrupt. This value is calculated based on a 472 ** maximum database size of 2^31 pages a minimum fanout of 2 for a 473 ** root-node and 3 for all other internal nodes. 474 ** 475 ** If a tree that appears to be taller than this is encountered, it is 476 ** assumed that the database is corrupt. 477 */ 478 #define BTCURSOR_MAX_DEPTH 20 479 480 /* 481 ** A cursor is a pointer to a particular entry within a particular 482 ** b-tree within a database file. 483 ** 484 ** The entry is identified by its MemPage and the index in 485 ** MemPage.aCell[] of the entry. 486 ** 487 ** A single database file can be shared by two more database connections, 488 ** but cursors cannot be shared. Each cursor is associated with a 489 ** particular database connection identified BtCursor.pBtree.db. 490 ** 491 ** Fields in this structure are accessed under the BtShared.mutex 492 ** found at self->pBt->mutex. 493 */ 494 struct BtCursor { 495 Btree *pBtree; /* The Btree to which this cursor belongs */ 496 BtShared *pBt; /* The BtShared this cursor points to */ 497 BtCursor *pNext, *pPrev; /* Forms a linked list of all cursors */ 498 struct KeyInfo *pKeyInfo; /* Argument passed to comparison function */ 499 #ifndef SQLITE_OMIT_INCRBLOB 500 Pgno *aOverflow; /* Cache of overflow page locations */ 501 #endif 502 Pgno pgnoRoot; /* The root page of this tree */ 503 sqlite3_int64 cachedRowid; /* Next rowid cache. 0 means not valid */ 504 CellInfo info; /* A parse of the cell we are pointing at */ 505 i64 nKey; /* Size of pKey, or last integer key */ 506 void *pKey; /* Saved key that was cursor's last known position */ 507 int skipNext; /* Prev() is noop if negative. Next() is noop if positive */ 508 u8 wrFlag; /* True if writable */ 509 u8 atLast; /* Cursor pointing to the last entry */ 510 u8 validNKey; /* True if info.nKey is valid */ 511 u8 eState; /* One of the CURSOR_XXX constants (see below) */ 512 #ifndef SQLITE_OMIT_INCRBLOB 513 u8 isIncrblobHandle; /* True if this cursor is an incr. io handle */ 514 #endif 515 u8 hints; /* As configured by CursorSetHints() */ 516 i16 iPage; /* Index of current page in apPage */ 517 u16 aiIdx[BTCURSOR_MAX_DEPTH]; /* Current index in apPage[i] */ 518 MemPage *apPage[BTCURSOR_MAX_DEPTH]; /* Pages from root to current page */ 519 }; 520 521 /* 522 ** Potential values for BtCursor.eState. 523 ** 524 ** CURSOR_INVALID: 525 ** Cursor does not point to a valid entry. This can happen (for example) 526 ** because the table is empty or because BtreeCursorFirst() has not been 527 ** called. 528 ** 529 ** CURSOR_VALID: 530 ** Cursor points to a valid entry. getPayload() etc. may be called. 531 ** 532 ** CURSOR_SKIPNEXT: 533 ** Cursor is valid except that the Cursor.skipNext field is non-zero 534 ** indicating that the next sqlite3BtreeNext() or sqlite3BtreePrevious() 535 ** operation should be a no-op. 536 ** 537 ** CURSOR_REQUIRESEEK: 538 ** The table that this cursor was opened on still exists, but has been 539 ** modified since the cursor was last used. The cursor position is saved 540 ** in variables BtCursor.pKey and BtCursor.nKey. When a cursor is in 541 ** this state, restoreCursorPosition() can be called to attempt to 542 ** seek the cursor to the saved position. 543 ** 544 ** CURSOR_FAULT: 545 ** A unrecoverable error (an I/O error or a malloc failure) has occurred 546 ** on a different connection that shares the BtShared cache with this 547 ** cursor. The error has left the cache in an inconsistent state. 548 ** Do nothing else with this cursor. Any attempt to use the cursor 549 ** should return the error code stored in BtCursor.skip 550 */ 551 #define CURSOR_INVALID 0 552 #define CURSOR_VALID 1 553 #define CURSOR_SKIPNEXT 2 554 #define CURSOR_REQUIRESEEK 3 555 #define CURSOR_FAULT 4 556 557 /* 558 ** The database page the PENDING_BYTE occupies. This page is never used. 559 */ 560 # define PENDING_BYTE_PAGE(pBt) PAGER_MJ_PGNO(pBt) 561 562 /* 563 ** These macros define the location of the pointer-map entry for a 564 ** database page. The first argument to each is the number of usable 565 ** bytes on each page of the database (often 1024). The second is the 566 ** page number to look up in the pointer map. 567 ** 568 ** PTRMAP_PAGENO returns the database page number of the pointer-map 569 ** page that stores the required pointer. PTRMAP_PTROFFSET returns 570 ** the offset of the requested map entry. 571 ** 572 ** If the pgno argument passed to PTRMAP_PAGENO is a pointer-map page, 573 ** then pgno is returned. So (pgno==PTRMAP_PAGENO(pgsz, pgno)) can be 574 ** used to test if pgno is a pointer-map page. PTRMAP_ISPAGE implements 575 ** this test. 576 */ 577 #define PTRMAP_PAGENO(pBt, pgno) ptrmapPageno(pBt, pgno) 578 #define PTRMAP_PTROFFSET(pgptrmap, pgno) (5*(pgno-pgptrmap-1)) 579 #define PTRMAP_ISPAGE(pBt, pgno) (PTRMAP_PAGENO((pBt),(pgno))==(pgno)) 580 581 /* 582 ** The pointer map is a lookup table that identifies the parent page for 583 ** each child page in the database file. The parent page is the page that 584 ** contains a pointer to the child. Every page in the database contains 585 ** 0 or 1 parent pages. (In this context 'database page' refers 586 ** to any page that is not part of the pointer map itself.) Each pointer map 587 ** entry consists of a single byte 'type' and a 4 byte parent page number. 588 ** The PTRMAP_XXX identifiers below are the valid types. 589 ** 590 ** The purpose of the pointer map is to facility moving pages from one 591 ** position in the file to another as part of autovacuum. When a page 592 ** is moved, the pointer in its parent must be updated to point to the 593 ** new location. The pointer map is used to locate the parent page quickly. 594 ** 595 ** PTRMAP_ROOTPAGE: The database page is a root-page. The page-number is not 596 ** used in this case. 597 ** 598 ** PTRMAP_FREEPAGE: The database page is an unused (free) page. The page-number 599 ** is not used in this case. 600 ** 601 ** PTRMAP_OVERFLOW1: The database page is the first page in a list of 602 ** overflow pages. The page number identifies the page that 603 ** contains the cell with a pointer to this overflow page. 604 ** 605 ** PTRMAP_OVERFLOW2: The database page is the second or later page in a list of 606 ** overflow pages. The page-number identifies the previous 607 ** page in the overflow page list. 608 ** 609 ** PTRMAP_BTREE: The database page is a non-root btree page. The page number 610 ** identifies the parent page in the btree. 611 */ 612 #define PTRMAP_ROOTPAGE 1 613 #define PTRMAP_FREEPAGE 2 614 #define PTRMAP_OVERFLOW1 3 615 #define PTRMAP_OVERFLOW2 4 616 #define PTRMAP_BTREE 5 617 618 /* A bunch of assert() statements to check the transaction state variables 619 ** of handle p (type Btree*) are internally consistent. 620 */ 621 #define btreeIntegrity(p) \ 622 assert( p->pBt->inTransaction!=TRANS_NONE || p->pBt->nTransaction==0 ); \ 623 assert( p->pBt->inTransaction>=p->inTrans ); 624 625 626 /* 627 ** The ISAUTOVACUUM macro is used within balance_nonroot() to determine 628 ** if the database supports auto-vacuum or not. Because it is used 629 ** within an expression that is an argument to another macro 630 ** (sqliteMallocRaw), it is not possible to use conditional compilation. 631 ** So, this macro is defined instead. 632 */ 633 #ifndef SQLITE_OMIT_AUTOVACUUM 634 #define ISAUTOVACUUM (pBt->autoVacuum) 635 #else 636 #define ISAUTOVACUUM 0 637 #endif 638 639 640 /* 641 ** This structure is passed around through all the sanity checking routines 642 ** in order to keep track of some global state information. 643 ** 644 ** The aRef[] array is allocated so that there is 1 bit for each page in 645 ** the database. As the integrity-check proceeds, for each page used in 646 ** the database the corresponding bit is set. This allows integrity-check to 647 ** detect pages that are used twice and orphaned pages (both of which 648 ** indicate corruption). 649 */ 650 typedef struct IntegrityCk IntegrityCk; 651 struct IntegrityCk { 652 BtShared *pBt; /* The tree being checked out */ 653 Pager *pPager; /* The associated pager. Also accessible by pBt->pPager */ 654 u8 *aPgRef; /* 1 bit per page in the db (see above) */ 655 Pgno nPage; /* Number of pages in the database */ 656 int mxErr; /* Stop accumulating errors when this reaches zero */ 657 int nErr; /* Number of messages written to zErrMsg so far */ 658 int mallocFailed; /* A memory allocation error has occurred */ 659 StrAccum errMsg; /* Accumulate the error message text here */ 660 }; 661 662 /* 663 ** Routines to read or write a two- and four-byte big-endian integer values. 664 */ 665 #define get2byte(x) ((x)[0]<<8 | (x)[1]) 666 #define put2byte(p,v) ((p)[0] = (u8)((v)>>8), (p)[1] = (u8)(v)) 667 #define get4byte sqlite3Get4byte 668 #define put4byte sqlite3Put4byte 669