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| 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 ** $Id: btreeInt.h,v 1.52 2009/07/15 17:25:46 drh Exp $ | |
| 13 ** | |
| 14 ** This file implements a external (disk-based) database using BTrees. | |
| 15 ** For a detailed discussion of BTrees, refer to | |
| 16 ** | |
| 17 ** Donald E. Knuth, THE ART OF COMPUTER PROGRAMMING, Volume 3: | |
| 18 ** "Sorting And Searching", pages 473-480. Addison-Wesley | |
| 19 ** Publishing Company, Reading, Massachusetts. | |
| 20 ** | |
| 21 ** The basic idea is that each page of the file contains N database | |
| 22 ** entries and N+1 pointers to subpages. | |
| 23 ** | |
| 24 ** ---------------------------------------------------------------- | |
| 25 ** | Ptr(0) | Key(0) | Ptr(1) | Key(1) | ... | Key(N-1) | Ptr(N) | | |
| 26 ** ---------------------------------------------------------------- | |
| 27 ** | |
| 28 ** All of the keys on the page that Ptr(0) points to have values less | |
| 29 ** than Key(0). All of the keys on page Ptr(1) and its subpages have | |
| 30 ** values greater than Key(0) and less than Key(1). All of the keys | |
| 31 ** on Ptr(N) and its subpages have values greater than Key(N-1). And | |
| 32 ** so forth. | |
| 33 ** | |
| 34 ** Finding a particular key requires reading O(log(M)) pages from the | |
| 35 ** disk where M is the number of entries in the tree. | |
| 36 ** | |
| 37 ** In this implementation, a single file can hold one or more separate | |
| 38 ** BTrees. Each BTree is identified by the index of its root page. The | |
| 39 ** key and data for any entry are combined to form the "payload". A | |
| 40 ** fixed amount of payload can be carried directly on the database | |
| 41 ** page. If the payload is larger than the preset amount then surplus | |
| 42 ** bytes are stored on overflow pages. The payload for an entry | |
| 43 ** and the preceding pointer are combined to form a "Cell". Each | |
| 44 ** page has a small header which contains the Ptr(N) pointer and other | |
| 45 ** information such as the size of key and data. | |
| 46 ** | |
| 47 ** FORMAT DETAILS | |
| 48 ** | |
| 49 ** The file is divided into pages. The first page is called page 1, | |
| 50 ** the second is page 2, and so forth. A page number of zero indicates | |
| 51 ** "no such page". The page size can be anything between 512 and 65536. | |
| 52 ** Each page can be either a btree page, a freelist page or an overflow | |
| 53 ** page. | |
| 54 ** | |
| 55 ** The first page is always a btree page. The first 100 bytes of the first | |
| 56 ** page contain a special header (the "file header") that describes the file. | |
| 57 ** The format of the file header is as follows: | |
| 58 ** | |
| 59 ** OFFSET SIZE DESCRIPTION | |
| 60 ** 0 16 Header string: "SQLite format 3\000" | |
| 61 ** 16 2 Page size in bytes. | |
| 62 ** 18 1 File format write version | |
| 63 ** 19 1 File format read version | |
| 64 ** 20 1 Bytes of unused space at the end of each page | |
| 65 ** 21 1 Max embedded payload fraction | |
| 66 ** 22 1 Min embedded payload fraction | |
| 67 ** 23 1 Min leaf payload fraction | |
| 68 ** 24 4 File change counter | |
| 69 ** 28 4 Reserved for future use | |
| 70 ** 32 4 First freelist page | |
| 71 ** 36 4 Number of freelist pages in the file | |
| 72 ** 40 60 15 4-byte meta values passed to higher layers | |
| 73 ** | |
| 74 ** 40 4 Schema cookie | |
| 75 ** 44 4 File format of schema layer | |
| 76 ** 48 4 Size of page cache | |
| 77 ** 52 4 Largest root-page (auto/incr_vacuum) | |
| 78 ** 56 4 1=UTF-8 2=UTF16le 3=UTF16be | |
| 79 ** 60 4 User version | |
| 80 ** 64 4 Incremental vacuum mode | |
| 81 ** 68 4 unused | |
| 82 ** 72 4 unused | |
| 83 ** 76 4 unused | |
| 84 ** | |
| 85 ** All of the integer values are big-endian (most significant byte first). | |
| 86 ** | |
| 87 ** The file change counter is incremented when the database is changed | |
| 88 ** This counter allows other processes to know when the file has changed | |
| 89 ** and thus when they need to flush their cache. | |
| 90 ** | |
| 91 ** The max embedded payload fraction is the amount of the total usable | |
| 92 ** space in a page that can be consumed by a single cell for standard | |
| 93 ** B-tree (non-LEAFDATA) tables. A value of 255 means 100%. The default | |
| 94 ** is to limit the maximum cell size so that at least 4 cells will fit | |
| 95 ** on one page. Thus the default max embedded payload fraction is 64. | |
| 96 ** | |
| 97 ** If the payload for a cell is larger than the max payload, then extra | |
| 98 ** payload is spilled to overflow pages. Once an overflow page is allocated, | |
| 99 ** as many bytes as possible are moved into the overflow pages without letting | |
| 100 ** the cell size drop below the min embedded payload fraction. | |
| 101 ** | |
| 102 ** The min leaf payload fraction is like the min embedded payload fraction | |
| 103 ** except that it applies to leaf nodes in a LEAFDATA tree. The maximum | |
| 104 ** payload fraction for a LEAFDATA tree is always 100% (or 255) and it | |
| 105 ** not specified in the header. | |
| 106 ** | |
| 107 ** Each btree pages is divided into three sections: The header, the | |
| 108 ** cell pointer array, and the cell content area. Page 1 also has a 100-byte | |
| 109 ** file header that occurs before the page header. | |
| 110 ** | |
| 111 ** |----------------| | |
| 112 ** | file header | 100 bytes. Page 1 only. | |
| 113 ** |----------------| | |
| 114 ** | page header | 8 bytes for leaves. 12 bytes for interior nodes | |
| 115 ** |----------------| | |
| 116 ** | cell pointer | | 2 bytes per cell. Sorted order. | |
| 117 ** | array | | Grows downward | |
| 118 ** | | v | |
| 119 ** |----------------| | |
| 120 ** | unallocated | | |
| 121 ** | space | | |
| 122 ** |----------------| ^ Grows upwards | |
| 123 ** | cell content | | Arbitrary order interspersed with freeblocks. | |
| 124 ** | area | | and free space fragments. | |
| 125 ** |----------------| | |
| 126 ** | |
| 127 ** The page headers looks like this: | |
| 128 ** | |
| 129 ** OFFSET SIZE DESCRIPTION | |
| 130 ** 0 1 Flags. 1: intkey, 2: zerodata, 4: leafdata, 8: leaf | |
| 131 ** 1 2 byte offset to the first freeblock | |
| 132 ** 3 2 number of cells on this page | |
| 133 ** 5 2 first byte of the cell content area | |
| 134 ** 7 1 number of fragmented free bytes | |
| 135 ** 8 4 Right child (the Ptr(N) value). Omitted on leaves. | |
| 136 ** | |
| 137 ** The flags define the format of this btree page. The leaf flag means that | |
| 138 ** this page has no children. The zerodata flag means that this page carries | |
| 139 ** only keys and no data. The intkey flag means that the key is a integer | |
| 140 ** which is stored in the key size entry of the cell header rather than in | |
| 141 ** the payload area. | |
| 142 ** | |
| 143 ** The cell pointer array begins on the first byte after the page header. | |
| 144 ** The cell pointer array contains zero or more 2-byte numbers which are | |
| 145 ** offsets from the beginning of the page to the cell content in the cell | |
| 146 ** content area. The cell pointers occur in sorted order. The system strives | |
| 147 ** to keep free space after the last cell pointer so that new cells can | |
| 148 ** be easily added without having to defragment the page. | |
| 149 ** | |
| 150 ** Cell content is stored at the very end of the page and grows toward the | |
| 151 ** beginning of the page. | |
| 152 ** | |
| 153 ** Unused space within the cell content area is collected into a linked list of | |
| 154 ** freeblocks. Each freeblock is at least 4 bytes in size. The byte offset | |
| 155 ** to the first freeblock is given in the header. Freeblocks occur in | |
| 156 ** increasing order. Because a freeblock must be at least 4 bytes in size, | |
| 157 ** any group of 3 or fewer unused bytes in the cell content area cannot | |
| 158 ** exist on the freeblock chain. A group of 3 or fewer free bytes is called | |
| 159 ** a fragment. The total number of bytes in all fragments is recorded. | |
| 160 ** in the page header at offset 7. | |
| 161 ** | |
| 162 ** SIZE DESCRIPTION | |
| 163 ** 2 Byte offset of the next freeblock | |
| 164 ** 2 Bytes in this freeblock | |
| 165 ** | |
| 166 ** Cells are of variable length. Cells are stored in the cell content area at | |
| 167 ** the end of the page. Pointers to the cells are in the cell pointer array | |
| 168 ** that immediately follows the page header. Cells is not necessarily | |
| 169 ** contiguous or in order, but cell pointers are contiguous and in order. | |
| 170 ** | |
| 171 ** Cell content makes use of variable length integers. A variable | |
| 172 ** length integer is 1 to 9 bytes where the lower 7 bits of each | |
| 173 ** byte are used. The integer consists of all bytes that have bit 8 set and | |
| 174 ** the first byte with bit 8 clear. The most significant byte of the integer | |
| 175 ** appears first. A variable-length integer may not be more than 9 bytes long. | |
| 176 ** As a special case, all 8 bytes of the 9th byte are used as data. This | |
| 177 ** allows a 64-bit integer to be encoded in 9 bytes. | |
| 178 ** | |
| 179 ** 0x00 becomes 0x00000000 | |
| 180 ** 0x7f becomes 0x0000007f | |
| 181 ** 0x81 0x00 becomes 0x00000080 | |
| 182 ** 0x82 0x00 becomes 0x00000100 | |
| 183 ** 0x80 0x7f becomes 0x0000007f | |
| 184 ** 0x8a 0x91 0xd1 0xac 0x78 becomes 0x12345678 | |
| 185 ** 0x81 0x81 0x81 0x81 0x01 becomes 0x10204081 | |
| 186 ** | |
| 187 ** Variable length integers are used for rowids and to hold the number of | |
| 188 ** bytes of key and data in a btree cell. | |
| 189 ** | |
| 190 ** The content of a cell looks like this: | |
| 191 ** | |
| 192 ** SIZE DESCRIPTION | |
| 193 ** 4 Page number of the left child. Omitted if leaf flag is set. | |
| 194 ** var Number of bytes of data. Omitted if the zerodata flag is set. | |
| 195 ** var Number of bytes of key. Or the key itself if intkey flag is set. | |
| 196 ** * Payload | |
| 197 ** 4 First page of the overflow chain. Omitted if no overflow | |
| 198 ** | |
| 199 ** Overflow pages form a linked list. Each page except the last is completely | |
| 200 ** filled with data (pagesize - 4 bytes). The last page can have as little | |
| 201 ** as 1 byte of data. | |
| 202 ** | |
| 203 ** SIZE DESCRIPTION | |
| 204 ** 4 Page number of next overflow page | |
| 205 ** * Data | |
| 206 ** | |
| 207 ** Freelist pages come in two subtypes: trunk pages and leaf pages. The | |
| 208 ** file header points to the first in a linked list of trunk page. Each trunk | |
| 209 ** page points to multiple leaf pages. The content of a leaf page is | |
| 210 ** unspecified. A trunk page looks like this: | |
| 211 ** | |
| 212 ** SIZE DESCRIPTION | |
| 213 ** 4 Page number of next trunk page | |
| 214 ** 4 Number of leaf pointers on this page | |
| 215 ** * zero or more pages numbers of leaves | |
| 216 */ | |
| 217 #include "sqliteInt.h" | |
| 218 | |
| 219 | |
| 220 /* The following value is the maximum cell size assuming a maximum page | |
| 221 ** size give above. | |
| 222 */ | |
| 223 #define MX_CELL_SIZE(pBt) (pBt->pageSize-8) | |
| 224 | |
| 225 /* The maximum number of cells on a single page of the database. This | |
| 226 ** assumes a minimum cell size of 6 bytes (4 bytes for the cell itself | |
| 227 ** plus 2 bytes for the index to the cell in the page header). Such | |
| 228 ** small cells will be rare, but they are possible. | |
| 229 */ | |
| 230 #define MX_CELL(pBt) ((pBt->pageSize-8)/6) | |
| 231 | |
| 232 /* Forward declarations */ | |
| 233 typedef struct MemPage MemPage; | |
| 234 typedef struct BtLock BtLock; | |
| 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_FILE_HEADER "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 ** As each page of the file is loaded into memory, an instance of the following | |
| 263 ** structure is appended and initialized to zero. This structure stores | |
| 264 ** information about the page that is decoded from the raw file page. | |
| 265 ** | |
| 266 ** The pParent field points back to the parent page. This allows us to | |
| 267 ** walk up the BTree from any leaf to the root. Care must be taken to | |
| 268 ** unref() the parent page pointer when this page is no longer referenced. | |
| 269 ** The pageDestructor() routine handles that chore. | |
| 270 ** | |
| 271 ** Access to all fields of this structure is controlled by the mutex | |
| 272 ** stored in MemPage.pBt->mutex. | |
| 273 */ | |
| 274 struct MemPage { | |
| 275 u8 isInit; /* True if previously initialized. MUST BE FIRST! */ | |
| 276 u8 nOverflow; /* Number of overflow cell bodies in aCell[] */ | |
| 277 u8 intKey; /* True if intkey flag is set */ | |
| 278 u8 leaf; /* True if leaf flag is set */ | |
| 279 u8 hasData; /* True if this page stores data */ | |
| 280 u8 hdrOffset; /* 100 for page 1. 0 otherwise */ | |
| 281 u8 childPtrSize; /* 0 if leaf==1. 4 if leaf==0 */ | |
| 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 struct _OvflCell { /* Cells that will not fit on aData[] */ | |
| 289 u8 *pCell; /* Pointers to the body of the overflow cell */ | |
| 290 u16 idx; /* Insert this cell before idx-th non-overflow cell */ | |
| 291 } aOvfl[5]; | |
| 292 BtShared *pBt; /* Pointer to BtShared that this page is part of */ | |
| 293 u8 *aData; /* Pointer to disk image of the page data */ | |
| 294 DbPage *pDbPage; /* Pager page handle */ | |
| 295 Pgno pgno; /* Page number for this page */ | |
| 296 }; | |
| 297 | |
| 298 /* | |
| 299 ** The in-memory image of a disk page has the auxiliary information appended | |
| 300 ** to the end. EXTRA_SIZE is the number of bytes of space needed to hold | |
| 301 ** that extra information. | |
| 302 */ | |
| 303 #define EXTRA_SIZE sizeof(MemPage) | |
| 304 | |
| 305 /* | |
| 306 ** A linked list of the following structures is stored at BtShared.pLock. | |
| 307 ** Locks are added (or upgraded from READ_LOCK to WRITE_LOCK) when a cursor | |
| 308 ** is opened on the table with root page BtShared.iTable. Locks are removed | |
| 309 ** from this list when a transaction is committed or rolled back, or when | |
| 310 ** a btree handle is closed. | |
| 311 */ | |
| 312 struct BtLock { | |
| 313 Btree *pBtree; /* Btree handle holding this lock */ | |
| 314 Pgno iTable; /* Root page of table */ | |
| 315 u8 eLock; /* READ_LOCK or WRITE_LOCK */ | |
| 316 BtLock *pNext; /* Next in BtShared.pLock list */ | |
| 317 }; | |
| 318 | |
| 319 /* Candidate values for BtLock.eLock */ | |
| 320 #define READ_LOCK 1 | |
| 321 #define WRITE_LOCK 2 | |
| 322 | |
| 323 /* A Btree handle | |
| 324 ** | |
| 325 ** A database connection contains a pointer to an instance of | |
| 326 ** this object for every database file that it has open. This structure | |
| 327 ** is opaque to the database connection. The database connection cannot | |
| 328 ** see the internals of this structure and only deals with pointers to | |
| 329 ** this structure. | |
| 330 ** | |
| 331 ** For some database files, the same underlying database cache might be | |
| 332 ** shared between multiple connections. In that case, each contection | |
| 333 ** has it own pointer to this object. But each instance of this object | |
| 334 ** points to the same BtShared object. The database cache and the | |
| 335 ** schema associated with the database file are all contained within | |
| 336 ** the BtShared object. | |
| 337 ** | |
| 338 ** All fields in this structure are accessed under sqlite3.mutex. | |
| 339 ** The pBt pointer itself may not be changed while there exists cursors | |
| 340 ** in the referenced BtShared that point back to this Btree since those | |
| 341 ** cursors have to do go through this Btree to find their BtShared and | |
| 342 ** they often do so without holding sqlite3.mutex. | |
| 343 */ | |
| 344 struct Btree { | |
| 345 sqlite3 *db; /* The database connection holding this btree */ | |
| 346 BtShared *pBt; /* Sharable content of this btree */ | |
| 347 u8 inTrans; /* TRANS_NONE, TRANS_READ or TRANS_WRITE */ | |
| 348 u8 sharable; /* True if we can share pBt with another db */ | |
| 349 u8 locked; /* True if db currently has pBt locked */ | |
| 350 int wantToLock; /* Number of nested calls to sqlite3BtreeEnter() */ | |
| 351 int nBackup; /* Number of backup operations reading this btree */ | |
| 352 Btree *pNext; /* List of other sharable Btrees from the same db */ | |
| 353 Btree *pPrev; /* Back pointer of the same list */ | |
| 354 #ifndef SQLITE_OMIT_SHARED_CACHE | |
| 355 BtLock lock; /* Object used to lock page 1 */ | |
| 356 #endif | |
| 357 }; | |
| 358 | |
| 359 /* | |
| 360 ** Btree.inTrans may take one of the following values. | |
| 361 ** | |
| 362 ** If the shared-data extension is enabled, there may be multiple users | |
| 363 ** of the Btree structure. At most one of these may open a write transaction, | |
| 364 ** but any number may have active read transactions. | |
| 365 */ | |
| 366 #define TRANS_NONE 0 | |
| 367 #define TRANS_READ 1 | |
| 368 #define TRANS_WRITE 2 | |
| 369 | |
| 370 /* | |
| 371 ** An instance of this object represents a single database file. | |
| 372 ** | |
| 373 ** A single database file can be in use as the same time by two | |
| 374 ** or more database connections. When two or more connections are | |
| 375 ** sharing the same database file, each connection has it own | |
| 376 ** private Btree object for the file and each of those Btrees points | |
| 377 ** to this one BtShared object. BtShared.nRef is the number of | |
| 378 ** connections currently sharing this database file. | |
| 379 ** | |
| 380 ** Fields in this structure are accessed under the BtShared.mutex | |
| 381 ** mutex, except for nRef and pNext which are accessed under the | |
| 382 ** global SQLITE_MUTEX_STATIC_MASTER mutex. The pPager field | |
| 383 ** may not be modified once it is initially set as long as nRef>0. | |
| 384 ** The pSchema field may be set once under BtShared.mutex and | |
| 385 ** thereafter is unchanged as long as nRef>0. | |
| 386 ** | |
| 387 ** isPending: | |
| 388 ** | |
| 389 ** If a BtShared client fails to obtain a write-lock on a database | |
| 390 ** table (because there exists one or more read-locks on the table), | |
| 391 ** the shared-cache enters 'pending-lock' state and isPending is | |
| 392 ** set to true. | |
| 393 ** | |
| 394 ** The shared-cache leaves the 'pending lock' state when either of | |
| 395 ** the following occur: | |
| 396 ** | |
| 397 ** 1) The current writer (BtShared.pWriter) concludes its transaction, OR | |
| 398 ** 2) The number of locks held by other connections drops to zero. | |
| 399 ** | |
| 400 ** while in the 'pending-lock' state, no connection may start a new | |
| 401 ** transaction. | |
| 402 ** | |
| 403 ** This feature is included to help prevent writer-starvation. | |
| 404 */ | |
| 405 struct BtShared { | |
| 406 Pager *pPager; /* The page cache */ | |
| 407 sqlite3 *db; /* Database connection currently using this Btree */ | |
| 408 BtCursor *pCursor; /* A list of all open cursors */ | |
| 409 MemPage *pPage1; /* First page of the database */ | |
| 410 u8 readOnly; /* True if the underlying file is readonly */ | |
| 411 u8 pageSizeFixed; /* True if the page size can no longer be changed */ | |
| 412 #ifndef SQLITE_OMIT_AUTOVACUUM | |
| 413 u8 autoVacuum; /* True if auto-vacuum is enabled */ | |
| 414 u8 incrVacuum; /* True if incr-vacuum is enabled */ | |
| 415 #endif | |
| 416 u16 pageSize; /* Total number of bytes on a page */ | |
| 417 u16 usableSize; /* Number of usable bytes on each page */ | |
| 418 u16 maxLocal; /* Maximum local payload in non-LEAFDATA tables */ | |
| 419 u16 minLocal; /* Minimum local payload in non-LEAFDATA tables */ | |
| 420 u16 maxLeaf; /* Maximum local payload in a LEAFDATA table */ | |
| 421 u16 minLeaf; /* Minimum local payload in a LEAFDATA table */ | |
| 422 u8 inTransaction; /* Transaction state */ | |
| 423 int nTransaction; /* Number of open transactions (read + write) */ | |
| 424 void *pSchema; /* Pointer to space allocated by sqlite3BtreeSchema() */ | |
| 425 void (*xFreeSchema)(void*); /* Destructor for BtShared.pSchema */ | |
| 426 sqlite3_mutex *mutex; /* Non-recursive mutex required to access this struct */ | |
| 427 Bitvec *pHasContent; /* Set of pages moved to free-list this transaction */ | |
| 428 #ifndef SQLITE_OMIT_SHARED_CACHE | |
| 429 int nRef; /* Number of references to this structure */ | |
| 430 BtShared *pNext; /* Next on a list of sharable BtShared structs */ | |
| 431 BtLock *pLock; /* List of locks held on this shared-btree struct */ | |
| 432 Btree *pWriter; /* Btree with currently open write transaction */ | |
| 433 u8 isExclusive; /* True if pWriter has an EXCLUSIVE lock on the db */ | |
| 434 u8 isPending; /* If waiting for read-locks to clear */ | |
| 435 #endif | |
| 436 u8 *pTmpSpace; /* BtShared.pageSize bytes of space for tmp use */ | |
| 437 }; | |
| 438 | |
| 439 /* | |
| 440 ** An instance of the following structure is used to hold information | |
| 441 ** about a cell. The parseCellPtr() function fills in this structure | |
| 442 ** based on information extract from the raw disk page. | |
| 443 */ | |
| 444 typedef struct CellInfo CellInfo; | |
| 445 struct CellInfo { | |
| 446 u8 *pCell; /* Pointer to the start of cell content */ | |
| 447 i64 nKey; /* The key for INTKEY tables, or number of bytes in key */ | |
| 448 u32 nData; /* Number of bytes of data */ | |
| 449 u32 nPayload; /* Total amount of payload */ | |
| 450 u16 nHeader; /* Size of the cell content header in bytes */ | |
| 451 u16 nLocal; /* Amount of payload held locally */ | |
| 452 u16 iOverflow; /* Offset to overflow page number. Zero if no overflow */ | |
| 453 u16 nSize; /* Size of the cell content on the main b-tree page */ | |
| 454 }; | |
| 455 | |
| 456 /* | |
| 457 ** Maximum depth of an SQLite B-Tree structure. Any B-Tree deeper than | |
| 458 ** this will be declared corrupt. This value is calculated based on a | |
| 459 ** maximum database size of 2^31 pages a minimum fanout of 2 for a | |
| 460 ** root-node and 3 for all other internal nodes. | |
| 461 ** | |
| 462 ** If a tree that appears to be taller than this is encountered, it is | |
| 463 ** assumed that the database is corrupt. | |
| 464 */ | |
| 465 #define BTCURSOR_MAX_DEPTH 20 | |
| 466 | |
| 467 /* | |
| 468 ** A cursor is a pointer to a particular entry within a particular | |
| 469 ** b-tree within a database file. | |
| 470 ** | |
| 471 ** The entry is identified by its MemPage and the index in | |
| 472 ** MemPage.aCell[] of the entry. | |
| 473 ** | |
| 474 ** When a single database file can shared by two more database connections, | |
| 475 ** but cursors cannot be shared. Each cursor is associated with a | |
| 476 ** particular database connection identified BtCursor.pBtree.db. | |
| 477 ** | |
| 478 ** Fields in this structure are accessed under the BtShared.mutex | |
| 479 ** found at self->pBt->mutex. | |
| 480 */ | |
| 481 struct BtCursor { | |
| 482 Btree *pBtree; /* The Btree to which this cursor belongs */ | |
| 483 BtShared *pBt; /* The BtShared this cursor points to */ | |
| 484 BtCursor *pNext, *pPrev; /* Forms a linked list of all cursors */ | |
| 485 struct KeyInfo *pKeyInfo; /* Argument passed to comparison function */ | |
| 486 Pgno pgnoRoot; /* The root page of this tree */ | |
| 487 sqlite3_int64 cachedRowid; /* Next rowid cache. 0 means not valid */ | |
| 488 CellInfo info; /* A parse of the cell we are pointing at */ | |
| 489 u8 wrFlag; /* True if writable */ | |
| 490 u8 atLast; /* Cursor pointing to the last entry */ | |
| 491 u8 validNKey; /* True if info.nKey is valid */ | |
| 492 u8 eState; /* One of the CURSOR_XXX constants (see below) */ | |
| 493 void *pKey; /* Saved key that was cursor's last known position */ | |
| 494 i64 nKey; /* Size of pKey, or last integer key */ | |
| 495 int skipNext; /* Prev() is noop if negative. Next() is noop if positive */ | |
| 496 #ifndef SQLITE_OMIT_INCRBLOB | |
| 497 u8 isIncrblobHandle; /* True if this cursor is an incr. io handle */ | |
| 498 Pgno *aOverflow; /* Cache of overflow page locations */ | |
| 499 #endif | |
| 500 i16 iPage; /* Index of current page in apPage */ | |
| 501 MemPage *apPage[BTCURSOR_MAX_DEPTH]; /* Pages from root to current page */ | |
| 502 u16 aiIdx[BTCURSOR_MAX_DEPTH]; /* Current index in apPage[i] */ | |
| 503 }; | |
| 504 | |
| 505 /* | |
| 506 ** Potential values for BtCursor.eState. | |
| 507 ** | |
| 508 ** CURSOR_VALID: | |
| 509 ** Cursor points to a valid entry. getPayload() etc. may be called. | |
| 510 ** | |
| 511 ** CURSOR_INVALID: | |
| 512 ** Cursor does not point to a valid entry. This can happen (for example) | |
| 513 ** because the table is empty or because BtreeCursorFirst() has not been | |
| 514 ** called. | |
| 515 ** | |
| 516 ** CURSOR_REQUIRESEEK: | |
| 517 ** The table that this cursor was opened on still exists, but has been | |
| 518 ** modified since the cursor was last used. The cursor position is saved | |
| 519 ** in variables BtCursor.pKey and BtCursor.nKey. When a cursor is in | |
| 520 ** this state, restoreCursorPosition() can be called to attempt to | |
| 521 ** seek the cursor to the saved position. | |
| 522 ** | |
| 523 ** CURSOR_FAULT: | |
| 524 ** A unrecoverable error (an I/O error or a malloc failure) has occurred | |
| 525 ** on a different connection that shares the BtShared cache with this | |
| 526 ** cursor. The error has left the cache in an inconsistent state. | |
| 527 ** Do nothing else with this cursor. Any attempt to use the cursor | |
| 528 ** should return the error code stored in BtCursor.skip | |
| 529 */ | |
| 530 #define CURSOR_INVALID 0 | |
| 531 #define CURSOR_VALID 1 | |
| 532 #define CURSOR_REQUIRESEEK 2 | |
| 533 #define CURSOR_FAULT 3 | |
| 534 | |
| 535 /* | |
| 536 ** The database page the PENDING_BYTE occupies. This page is never used. | |
| 537 */ | |
| 538 # define PENDING_BYTE_PAGE(pBt) PAGER_MJ_PGNO(pBt) | |
| 539 | |
| 540 /* | |
| 541 ** These macros define the location of the pointer-map entry for a | |
| 542 ** database page. The first argument to each is the number of usable | |
| 543 ** bytes on each page of the database (often 1024). The second is the | |
| 544 ** page number to look up in the pointer map. | |
| 545 ** | |
| 546 ** PTRMAP_PAGENO returns the database page number of the pointer-map | |
| 547 ** page that stores the required pointer. PTRMAP_PTROFFSET returns | |
| 548 ** the offset of the requested map entry. | |
| 549 ** | |
| 550 ** If the pgno argument passed to PTRMAP_PAGENO is a pointer-map page, | |
| 551 ** then pgno is returned. So (pgno==PTRMAP_PAGENO(pgsz, pgno)) can be | |
| 552 ** used to test if pgno is a pointer-map page. PTRMAP_ISPAGE implements | |
| 553 ** this test. | |
| 554 */ | |
| 555 #define PTRMAP_PAGENO(pBt, pgno) ptrmapPageno(pBt, pgno) | |
| 556 #define PTRMAP_PTROFFSET(pgptrmap, pgno) (5*(pgno-pgptrmap-1)) | |
| 557 #define PTRMAP_ISPAGE(pBt, pgno) (PTRMAP_PAGENO((pBt),(pgno))==(pgno)) | |
| 558 | |
| 559 /* | |
| 560 ** The pointer map is a lookup table that identifies the parent page for | |
| 561 ** each child page in the database file. The parent page is the page that | |
| 562 ** contains a pointer to the child. Every page in the database contains | |
| 563 ** 0 or 1 parent pages. (In this context 'database page' refers | |
| 564 ** to any page that is not part of the pointer map itself.) Each pointer map | |
| 565 ** entry consists of a single byte 'type' and a 4 byte parent page number. | |
| 566 ** The PTRMAP_XXX identifiers below are the valid types. | |
| 567 ** | |
| 568 ** The purpose of the pointer map is to facility moving pages from one | |
| 569 ** position in the file to another as part of autovacuum. When a page | |
| 570 ** is moved, the pointer in its parent must be updated to point to the | |
| 571 ** new location. The pointer map is used to locate the parent page quickly. | |
| 572 ** | |
| 573 ** PTRMAP_ROOTPAGE: The database page is a root-page. The page-number is not | |
| 574 ** used in this case. | |
| 575 ** | |
| 576 ** PTRMAP_FREEPAGE: The database page is an unused (free) page. The page-number | |
| 577 ** is not used in this case. | |
| 578 ** | |
| 579 ** PTRMAP_OVERFLOW1: The database page is the first page in a list of | |
| 580 ** overflow pages. The page number identifies the page that | |
| 581 ** contains the cell with a pointer to this overflow page. | |
| 582 ** | |
| 583 ** PTRMAP_OVERFLOW2: The database page is the second or later page in a list of | |
| 584 ** overflow pages. The page-number identifies the previous | |
| 585 ** page in the overflow page list. | |
| 586 ** | |
| 587 ** PTRMAP_BTREE: The database page is a non-root btree page. The page number | |
| 588 ** identifies the parent page in the btree. | |
| 589 */ | |
| 590 #define PTRMAP_ROOTPAGE 1 | |
| 591 #define PTRMAP_FREEPAGE 2 | |
| 592 #define PTRMAP_OVERFLOW1 3 | |
| 593 #define PTRMAP_OVERFLOW2 4 | |
| 594 #define PTRMAP_BTREE 5 | |
| 595 | |
| 596 /* A bunch of assert() statements to check the transaction state variables | |
| 597 ** of handle p (type Btree*) are internally consistent. | |
| 598 */ | |
| 599 #define btreeIntegrity(p) \ | |
| 600 assert( p->pBt->inTransaction!=TRANS_NONE || p->pBt->nTransaction==0 ); \ | |
| 601 assert( p->pBt->inTransaction>=p->inTrans ); | |
| 602 | |
| 603 | |
| 604 /* | |
| 605 ** The ISAUTOVACUUM macro is used within balance_nonroot() to determine | |
| 606 ** if the database supports auto-vacuum or not. Because it is used | |
| 607 ** within an expression that is an argument to another macro | |
| 608 ** (sqliteMallocRaw), it is not possible to use conditional compilation. | |
| 609 ** So, this macro is defined instead. | |
| 610 */ | |
| 611 #ifndef SQLITE_OMIT_AUTOVACUUM | |
| 612 #define ISAUTOVACUUM (pBt->autoVacuum) | |
| 613 #else | |
| 614 #define ISAUTOVACUUM 0 | |
| 615 #endif | |
| 616 | |
| 617 | |
| 618 /* | |
| 619 ** This structure is passed around through all the sanity checking routines | |
| 620 ** in order to keep track of some global state information. | |
| 621 */ | |
| 622 typedef struct IntegrityCk IntegrityCk; | |
| 623 struct IntegrityCk { | |
| 624 BtShared *pBt; /* The tree being checked out */ | |
| 625 Pager *pPager; /* The associated pager. Also accessible by pBt->pPager */ | |
| 626 Pgno nPage; /* Number of pages in the database */ | |
| 627 int *anRef; /* Number of times each page is referenced */ | |
| 628 int mxErr; /* Stop accumulating errors when this reaches zero */ | |
| 629 int nErr; /* Number of messages written to zErrMsg so far */ | |
| 630 int mallocFailed; /* A memory allocation error has occurred */ | |
| 631 StrAccum errMsg; /* Accumulate the error message text here */ | |
| 632 }; | |
| 633 | |
| 634 /* | |
| 635 ** Read or write a two- and four-byte big-endian integer values. | |
| 636 */ | |
| 637 #define get2byte(x) ((x)[0]<<8 | (x)[1]) | |
| 638 #define put2byte(p,v) ((p)[0] = (u8)((v)>>8), (p)[1] = (u8)(v)) | |
| 639 #define get4byte sqlite3Get4byte | |
| 640 #define put4byte sqlite3Put4byte | |
| OLD | NEW |
|---|
Chromium Code Reviews
Issue 3108030:
Move bundled copy of sqlite one level deeper to better separate it... (Closed)
Base URL: svn://svn.chromium.org/chrome/trunk/src/