Annotation of embedaddon/sqlite3/src/btreeInt.h, revision 1.1
1.1 ! misho 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.
! 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
! 64: ** 22 1 Min embedded payload fraction
! 65: ** 23 1 Min leaf payload fraction
! 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 unused
! 80: ** 72 4 unused
! 81: ** 76 4 unused
! 82: **
! 83: ** All of the integer values are big-endian (most significant byte first).
! 84: **
! 85: ** The file change counter is incremented when the database is changed
! 86: ** This counter allows other processes to know when the file has changed
! 87: ** and thus when they need to flush their cache.
! 88: **
! 89: ** The max embedded payload fraction is the amount of the total usable
! 90: ** space in a page that can be consumed by a single cell for standard
! 91: ** B-tree (non-LEAFDATA) tables. A value of 255 means 100%. The default
! 92: ** is to limit the maximum cell size so that at least 4 cells will fit
! 93: ** on one page. Thus the default max embedded payload fraction is 64.
! 94: **
! 95: ** If the payload for a cell is larger than the max payload, then extra
! 96: ** payload is spilled to overflow pages. Once an overflow page is allocated,
! 97: ** as many bytes as possible are moved into the overflow pages without letting
! 98: ** the cell size drop below the min embedded payload fraction.
! 99: **
! 100: ** The min leaf payload fraction is like the min embedded payload fraction
! 101: ** except that it applies to leaf nodes in a LEAFDATA tree. The maximum
! 102: ** payload fraction for a LEAFDATA tree is always 100% (or 255) and it
! 103: ** not specified in the header.
! 104: **
! 105: ** Each btree pages is divided into three sections: The header, the
! 106: ** cell pointer array, and the cell content area. Page 1 also has a 100-byte
! 107: ** file header that occurs before the page header.
! 108: **
! 109: ** |----------------|
! 110: ** | file header | 100 bytes. Page 1 only.
! 111: ** |----------------|
! 112: ** | page header | 8 bytes for leaves. 12 bytes for interior nodes
! 113: ** |----------------|
! 114: ** | cell pointer | | 2 bytes per cell. Sorted order.
! 115: ** | array | | Grows downward
! 116: ** | | v
! 117: ** |----------------|
! 118: ** | unallocated |
! 119: ** | space |
! 120: ** |----------------| ^ Grows upwards
! 121: ** | cell content | | Arbitrary order interspersed with freeblocks.
! 122: ** | area | | and free space fragments.
! 123: ** |----------------|
! 124: **
! 125: ** The page headers looks like this:
! 126: **
! 127: ** OFFSET SIZE DESCRIPTION
! 128: ** 0 1 Flags. 1: intkey, 2: zerodata, 4: leafdata, 8: leaf
! 129: ** 1 2 byte offset to the first freeblock
! 130: ** 3 2 number of cells on this page
! 131: ** 5 2 first byte of the cell content area
! 132: ** 7 1 number of fragmented free bytes
! 133: ** 8 4 Right child (the Ptr(N) value). Omitted on leaves.
! 134: **
! 135: ** The flags define the format of this btree page. The leaf flag means that
! 136: ** this page has no children. The zerodata flag means that this page carries
! 137: ** only keys and no data. The intkey flag means that the key is a integer
! 138: ** which is stored in the key size entry of the cell header rather than in
! 139: ** the payload area.
! 140: **
! 141: ** The cell pointer array begins on the first byte after the page header.
! 142: ** The cell pointer array contains zero or more 2-byte numbers which are
! 143: ** offsets from the beginning of the page to the cell content in the cell
! 144: ** content area. The cell pointers occur in sorted order. The system strives
! 145: ** to keep free space after the last cell pointer so that new cells can
! 146: ** be easily added without having to defragment the page.
! 147: **
! 148: ** Cell content is stored at the very end of the page and grows toward the
! 149: ** beginning of the page.
! 150: **
! 151: ** Unused space within the cell content area is collected into a linked list of
! 152: ** freeblocks. Each freeblock is at least 4 bytes in size. The byte offset
! 153: ** to the first freeblock is given in the header. Freeblocks occur in
! 154: ** increasing order. Because a freeblock must be at least 4 bytes in size,
! 155: ** any group of 3 or fewer unused bytes in the cell content area cannot
! 156: ** exist on the freeblock chain. A group of 3 or fewer free bytes is called
! 157: ** a fragment. The total number of bytes in all fragments is recorded.
! 158: ** in the page header at offset 7.
! 159: **
! 160: ** SIZE DESCRIPTION
! 161: ** 2 Byte offset of the next freeblock
! 162: ** 2 Bytes in this freeblock
! 163: **
! 164: ** Cells are of variable length. Cells are stored in the cell content area at
! 165: ** the end of the page. Pointers to the cells are in the cell pointer array
! 166: ** that immediately follows the page header. Cells is not necessarily
! 167: ** contiguous or in order, but cell pointers are contiguous and in order.
! 168: **
! 169: ** Cell content makes use of variable length integers. A variable
! 170: ** length integer is 1 to 9 bytes where the lower 7 bits of each
! 171: ** byte are used. The integer consists of all bytes that have bit 8 set and
! 172: ** the first byte with bit 8 clear. The most significant byte of the integer
! 173: ** appears first. A variable-length integer may not be more than 9 bytes long.
! 174: ** As a special case, all 8 bytes of the 9th byte are used as data. This
! 175: ** allows a 64-bit integer to be encoded in 9 bytes.
! 176: **
! 177: ** 0x00 becomes 0x00000000
! 178: ** 0x7f becomes 0x0000007f
! 179: ** 0x81 0x00 becomes 0x00000080
! 180: ** 0x82 0x00 becomes 0x00000100
! 181: ** 0x80 0x7f becomes 0x0000007f
! 182: ** 0x8a 0x91 0xd1 0xac 0x78 becomes 0x12345678
! 183: ** 0x81 0x81 0x81 0x81 0x01 becomes 0x10204081
! 184: **
! 185: ** Variable length integers are used for rowids and to hold the number of
! 186: ** bytes of key and data in a btree cell.
! 187: **
! 188: ** The content of a cell looks like this:
! 189: **
! 190: ** SIZE DESCRIPTION
! 191: ** 4 Page number of the left child. Omitted if leaf flag is set.
! 192: ** var Number of bytes of data. Omitted if the zerodata flag is set.
! 193: ** var Number of bytes of key. Or the key itself if intkey flag is set.
! 194: ** * Payload
! 195: ** 4 First page of the overflow chain. Omitted if no overflow
! 196: **
! 197: ** Overflow pages form a linked list. Each page except the last is completely
! 198: ** filled with data (pagesize - 4 bytes). The last page can have as little
! 199: ** as 1 byte of data.
! 200: **
! 201: ** SIZE DESCRIPTION
! 202: ** 4 Page number of next overflow page
! 203: ** * Data
! 204: **
! 205: ** Freelist pages come in two subtypes: trunk pages and leaf pages. The
! 206: ** file header points to the first in a linked list of trunk page. Each trunk
! 207: ** page points to multiple leaf pages. The content of a leaf page is
! 208: ** unspecified. A trunk page looks like this:
! 209: **
! 210: ** SIZE DESCRIPTION
! 211: ** 4 Page number of next trunk page
! 212: ** 4 Number of leaf pointers on this page
! 213: ** * zero or more pages numbers of leaves
! 214: */
! 215: #include "sqliteInt.h"
! 216:
! 217:
! 218: /* The following value is the maximum cell size assuming a maximum page
! 219: ** size give above.
! 220: */
! 221: #define MX_CELL_SIZE(pBt) ((int)(pBt->pageSize-8))
! 222:
! 223: /* The maximum number of cells on a single page of the database. This
! 224: ** assumes a minimum cell size of 6 bytes (4 bytes for the cell itself
! 225: ** plus 2 bytes for the index to the cell in the page header). Such
! 226: ** small cells will be rare, but they are possible.
! 227: */
! 228: #define MX_CELL(pBt) ((pBt->pageSize-8)/6)
! 229:
! 230: /* Forward declarations */
! 231: typedef struct MemPage MemPage;
! 232: typedef struct BtLock BtLock;
! 233:
! 234: /*
! 235: ** This is a magic string that appears at the beginning of every
! 236: ** SQLite database in order to identify the file as a real database.
! 237: **
! 238: ** You can change this value at compile-time by specifying a
! 239: ** -DSQLITE_FILE_HEADER="..." on the compiler command-line. The
! 240: ** header must be exactly 16 bytes including the zero-terminator so
! 241: ** the string itself should be 15 characters long. If you change
! 242: ** the header, then your custom library will not be able to read
! 243: ** databases generated by the standard tools and the standard tools
! 244: ** will not be able to read databases created by your custom library.
! 245: */
! 246: #ifndef SQLITE_FILE_HEADER /* 123456789 123456 */
! 247: # define SQLITE_FILE_HEADER "SQLite format 3"
! 248: #endif
! 249:
! 250: /*
! 251: ** Page type flags. An ORed combination of these flags appear as the
! 252: ** first byte of on-disk image of every BTree page.
! 253: */
! 254: #define PTF_INTKEY 0x01
! 255: #define PTF_ZERODATA 0x02
! 256: #define PTF_LEAFDATA 0x04
! 257: #define PTF_LEAF 0x08
! 258:
! 259: /*
! 260: ** As each page of the file is loaded into memory, an instance of the following
! 261: ** structure is appended and initialized to zero. This structure stores
! 262: ** information about the page that is decoded from the raw file page.
! 263: **
! 264: ** The pParent field points back to the parent page. This allows us to
! 265: ** walk up the BTree from any leaf to the root. Care must be taken to
! 266: ** unref() the parent page pointer when this page is no longer referenced.
! 267: ** The pageDestructor() routine handles that chore.
! 268: **
! 269: ** Access to all fields of this structure is controlled by the mutex
! 270: ** stored in MemPage.pBt->mutex.
! 271: */
! 272: struct MemPage {
! 273: u8 isInit; /* True if previously initialized. MUST BE FIRST! */
! 274: u8 nOverflow; /* Number of overflow cell bodies in aCell[] */
! 275: u8 intKey; /* True if intkey flag is set */
! 276: u8 leaf; /* True if leaf flag is set */
! 277: u8 hasData; /* True if this page stores data */
! 278: u8 hdrOffset; /* 100 for page 1. 0 otherwise */
! 279: u8 childPtrSize; /* 0 if leaf==1. 4 if leaf==0 */
! 280: u8 max1bytePayload; /* min(maxLocal,127) */
! 281: u16 maxLocal; /* Copy of BtShared.maxLocal or BtShared.maxLeaf */
! 282: u16 minLocal; /* Copy of BtShared.minLocal or BtShared.minLeaf */
! 283: u16 cellOffset; /* Index in aData of first cell pointer */
! 284: u16 nFree; /* Number of free bytes on the page */
! 285: u16 nCell; /* Number of cells on this page, local and ovfl */
! 286: u16 maskPage; /* Mask for page offset */
! 287: struct _OvflCell { /* Cells that will not fit on aData[] */
! 288: u8 *pCell; /* Pointers to the body of the overflow cell */
! 289: u16 idx; /* Insert this cell before idx-th non-overflow cell */
! 290: } aOvfl[5];
! 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: #endif
! 416: u8 inTransaction; /* Transaction state */
! 417: u8 max1bytePayload; /* Maximum first byte of cell for a 1-byte payload */
! 418: u16 btsFlags; /* Boolean parameters. See BTS_* macros below */
! 419: u16 maxLocal; /* Maximum local payload in non-LEAFDATA tables */
! 420: u16 minLocal; /* Minimum local payload in non-LEAFDATA tables */
! 421: u16 maxLeaf; /* Maximum local payload in a LEAFDATA table */
! 422: u16 minLeaf; /* Minimum local payload in a LEAFDATA table */
! 423: u32 pageSize; /* Total number of bytes on a page */
! 424: u32 usableSize; /* Number of usable bytes on each page */
! 425: int nTransaction; /* Number of open transactions (read + write) */
! 426: u32 nPage; /* Number of pages in the database */
! 427: void *pSchema; /* Pointer to space allocated by sqlite3BtreeSchema() */
! 428: void (*xFreeSchema)(void*); /* Destructor for BtShared.pSchema */
! 429: sqlite3_mutex *mutex; /* Non-recursive mutex required to access this object */
! 430: Bitvec *pHasContent; /* Set of pages moved to free-list this transaction */
! 431: #ifndef SQLITE_OMIT_SHARED_CACHE
! 432: int nRef; /* Number of references to this structure */
! 433: BtShared *pNext; /* Next on a list of sharable BtShared structs */
! 434: BtLock *pLock; /* List of locks held on this shared-btree struct */
! 435: Btree *pWriter; /* Btree with currently open write transaction */
! 436: #endif
! 437: u8 *pTmpSpace; /* BtShared.pageSize bytes of space for tmp use */
! 438: };
! 439:
! 440: /*
! 441: ** Allowed values for BtShared.btsFlags
! 442: */
! 443: #define BTS_READ_ONLY 0x0001 /* Underlying file is readonly */
! 444: #define BTS_PAGESIZE_FIXED 0x0002 /* Page size can no longer be changed */
! 445: #define BTS_SECURE_DELETE 0x0004 /* PRAGMA secure_delete is enabled */
! 446: #define BTS_INITIALLY_EMPTY 0x0008 /* Database was empty at trans start */
! 447: #define BTS_NO_WAL 0x0010 /* Do not open write-ahead-log files */
! 448: #define BTS_EXCLUSIVE 0x0020 /* pWriter has an exclusive lock */
! 449: #define BTS_PENDING 0x0040 /* Waiting for read-locks to clear */
! 450:
! 451: /*
! 452: ** An instance of the following structure is used to hold information
! 453: ** about a cell. The parseCellPtr() function fills in this structure
! 454: ** based on information extract from the raw disk page.
! 455: */
! 456: typedef struct CellInfo CellInfo;
! 457: struct CellInfo {
! 458: i64 nKey; /* The key for INTKEY tables, or number of bytes in key */
! 459: u8 *pCell; /* Pointer to the start of cell content */
! 460: u32 nData; /* Number of bytes of data */
! 461: u32 nPayload; /* Total amount of payload */
! 462: u16 nHeader; /* Size of the cell content header in bytes */
! 463: u16 nLocal; /* Amount of payload held locally */
! 464: u16 iOverflow; /* Offset to overflow page number. Zero if no overflow */
! 465: u16 nSize; /* Size of the cell content on the main b-tree page */
! 466: };
! 467:
! 468: /*
! 469: ** Maximum depth of an SQLite B-Tree structure. Any B-Tree deeper than
! 470: ** this will be declared corrupt. This value is calculated based on a
! 471: ** maximum database size of 2^31 pages a minimum fanout of 2 for a
! 472: ** root-node and 3 for all other internal nodes.
! 473: **
! 474: ** If a tree that appears to be taller than this is encountered, it is
! 475: ** assumed that the database is corrupt.
! 476: */
! 477: #define BTCURSOR_MAX_DEPTH 20
! 478:
! 479: /*
! 480: ** A cursor is a pointer to a particular entry within a particular
! 481: ** b-tree within a database file.
! 482: **
! 483: ** The entry is identified by its MemPage and the index in
! 484: ** MemPage.aCell[] of the entry.
! 485: **
! 486: ** A single database file can be shared by two more database connections,
! 487: ** but cursors cannot be shared. Each cursor is associated with a
! 488: ** particular database connection identified BtCursor.pBtree.db.
! 489: **
! 490: ** Fields in this structure are accessed under the BtShared.mutex
! 491: ** found at self->pBt->mutex.
! 492: */
! 493: struct BtCursor {
! 494: Btree *pBtree; /* The Btree to which this cursor belongs */
! 495: BtShared *pBt; /* The BtShared this cursor points to */
! 496: BtCursor *pNext, *pPrev; /* Forms a linked list of all cursors */
! 497: struct KeyInfo *pKeyInfo; /* Argument passed to comparison function */
! 498: Pgno pgnoRoot; /* The root page of this tree */
! 499: sqlite3_int64 cachedRowid; /* Next rowid cache. 0 means not valid */
! 500: CellInfo info; /* A parse of the cell we are pointing at */
! 501: i64 nKey; /* Size of pKey, or last integer key */
! 502: void *pKey; /* Saved key that was cursor's last known position */
! 503: int skipNext; /* Prev() is noop if negative. Next() is noop if positive */
! 504: u8 wrFlag; /* True if writable */
! 505: u8 atLast; /* Cursor pointing to the last entry */
! 506: u8 validNKey; /* True if info.nKey is valid */
! 507: u8 eState; /* One of the CURSOR_XXX constants (see below) */
! 508: #ifndef SQLITE_OMIT_INCRBLOB
! 509: Pgno *aOverflow; /* Cache of overflow page locations */
! 510: u8 isIncrblobHandle; /* True if this cursor is an incr. io handle */
! 511: #endif
! 512: i16 iPage; /* Index of current page in apPage */
! 513: u16 aiIdx[BTCURSOR_MAX_DEPTH]; /* Current index in apPage[i] */
! 514: MemPage *apPage[BTCURSOR_MAX_DEPTH]; /* Pages from root to current page */
! 515: };
! 516:
! 517: /*
! 518: ** Potential values for BtCursor.eState.
! 519: **
! 520: ** CURSOR_VALID:
! 521: ** Cursor points to a valid entry. getPayload() etc. may be called.
! 522: **
! 523: ** CURSOR_INVALID:
! 524: ** Cursor does not point to a valid entry. This can happen (for example)
! 525: ** because the table is empty or because BtreeCursorFirst() has not been
! 526: ** called.
! 527: **
! 528: ** CURSOR_REQUIRESEEK:
! 529: ** The table that this cursor was opened on still exists, but has been
! 530: ** modified since the cursor was last used. The cursor position is saved
! 531: ** in variables BtCursor.pKey and BtCursor.nKey. When a cursor is in
! 532: ** this state, restoreCursorPosition() can be called to attempt to
! 533: ** seek the cursor to the saved position.
! 534: **
! 535: ** CURSOR_FAULT:
! 536: ** A unrecoverable error (an I/O error or a malloc failure) has occurred
! 537: ** on a different connection that shares the BtShared cache with this
! 538: ** cursor. The error has left the cache in an inconsistent state.
! 539: ** Do nothing else with this cursor. Any attempt to use the cursor
! 540: ** should return the error code stored in BtCursor.skip
! 541: */
! 542: #define CURSOR_INVALID 0
! 543: #define CURSOR_VALID 1
! 544: #define CURSOR_REQUIRESEEK 2
! 545: #define CURSOR_FAULT 3
! 546:
! 547: /*
! 548: ** The database page the PENDING_BYTE occupies. This page is never used.
! 549: */
! 550: # define PENDING_BYTE_PAGE(pBt) PAGER_MJ_PGNO(pBt)
! 551:
! 552: /*
! 553: ** These macros define the location of the pointer-map entry for a
! 554: ** database page. The first argument to each is the number of usable
! 555: ** bytes on each page of the database (often 1024). The second is the
! 556: ** page number to look up in the pointer map.
! 557: **
! 558: ** PTRMAP_PAGENO returns the database page number of the pointer-map
! 559: ** page that stores the required pointer. PTRMAP_PTROFFSET returns
! 560: ** the offset of the requested map entry.
! 561: **
! 562: ** If the pgno argument passed to PTRMAP_PAGENO is a pointer-map page,
! 563: ** then pgno is returned. So (pgno==PTRMAP_PAGENO(pgsz, pgno)) can be
! 564: ** used to test if pgno is a pointer-map page. PTRMAP_ISPAGE implements
! 565: ** this test.
! 566: */
! 567: #define PTRMAP_PAGENO(pBt, pgno) ptrmapPageno(pBt, pgno)
! 568: #define PTRMAP_PTROFFSET(pgptrmap, pgno) (5*(pgno-pgptrmap-1))
! 569: #define PTRMAP_ISPAGE(pBt, pgno) (PTRMAP_PAGENO((pBt),(pgno))==(pgno))
! 570:
! 571: /*
! 572: ** The pointer map is a lookup table that identifies the parent page for
! 573: ** each child page in the database file. The parent page is the page that
! 574: ** contains a pointer to the child. Every page in the database contains
! 575: ** 0 or 1 parent pages. (In this context 'database page' refers
! 576: ** to any page that is not part of the pointer map itself.) Each pointer map
! 577: ** entry consists of a single byte 'type' and a 4 byte parent page number.
! 578: ** The PTRMAP_XXX identifiers below are the valid types.
! 579: **
! 580: ** The purpose of the pointer map is to facility moving pages from one
! 581: ** position in the file to another as part of autovacuum. When a page
! 582: ** is moved, the pointer in its parent must be updated to point to the
! 583: ** new location. The pointer map is used to locate the parent page quickly.
! 584: **
! 585: ** PTRMAP_ROOTPAGE: The database page is a root-page. The page-number is not
! 586: ** used in this case.
! 587: **
! 588: ** PTRMAP_FREEPAGE: The database page is an unused (free) page. The page-number
! 589: ** is not used in this case.
! 590: **
! 591: ** PTRMAP_OVERFLOW1: The database page is the first page in a list of
! 592: ** overflow pages. The page number identifies the page that
! 593: ** contains the cell with a pointer to this overflow page.
! 594: **
! 595: ** PTRMAP_OVERFLOW2: The database page is the second or later page in a list of
! 596: ** overflow pages. The page-number identifies the previous
! 597: ** page in the overflow page list.
! 598: **
! 599: ** PTRMAP_BTREE: The database page is a non-root btree page. The page number
! 600: ** identifies the parent page in the btree.
! 601: */
! 602: #define PTRMAP_ROOTPAGE 1
! 603: #define PTRMAP_FREEPAGE 2
! 604: #define PTRMAP_OVERFLOW1 3
! 605: #define PTRMAP_OVERFLOW2 4
! 606: #define PTRMAP_BTREE 5
! 607:
! 608: /* A bunch of assert() statements to check the transaction state variables
! 609: ** of handle p (type Btree*) are internally consistent.
! 610: */
! 611: #define btreeIntegrity(p) \
! 612: assert( p->pBt->inTransaction!=TRANS_NONE || p->pBt->nTransaction==0 ); \
! 613: assert( p->pBt->inTransaction>=p->inTrans );
! 614:
! 615:
! 616: /*
! 617: ** The ISAUTOVACUUM macro is used within balance_nonroot() to determine
! 618: ** if the database supports auto-vacuum or not. Because it is used
! 619: ** within an expression that is an argument to another macro
! 620: ** (sqliteMallocRaw), it is not possible to use conditional compilation.
! 621: ** So, this macro is defined instead.
! 622: */
! 623: #ifndef SQLITE_OMIT_AUTOVACUUM
! 624: #define ISAUTOVACUUM (pBt->autoVacuum)
! 625: #else
! 626: #define ISAUTOVACUUM 0
! 627: #endif
! 628:
! 629:
! 630: /*
! 631: ** This structure is passed around through all the sanity checking routines
! 632: ** in order to keep track of some global state information.
! 633: */
! 634: typedef struct IntegrityCk IntegrityCk;
! 635: struct IntegrityCk {
! 636: BtShared *pBt; /* The tree being checked out */
! 637: Pager *pPager; /* The associated pager. Also accessible by pBt->pPager */
! 638: Pgno nPage; /* Number of pages in the database */
! 639: int *anRef; /* Number of times each page is referenced */
! 640: int mxErr; /* Stop accumulating errors when this reaches zero */
! 641: int nErr; /* Number of messages written to zErrMsg so far */
! 642: int mallocFailed; /* A memory allocation error has occurred */
! 643: StrAccum errMsg; /* Accumulate the error message text here */
! 644: };
! 645:
! 646: /*
! 647: ** Routines to read or write a two- and four-byte big-endian integer values.
! 648: */
! 649: #define get2byte(x) ((x)[0]<<8 | (x)[1])
! 650: #define put2byte(p,v) ((p)[0] = (u8)((v)>>8), (p)[1] = (u8)(v))
! 651: #define get4byte sqlite3Get4byte
! 652: #define put4byte sqlite3Put4byte
FreeBSD-CVSweb <freebsd-cvsweb@FreeBSD.org>
![[BACK]](/icons/cvsweb/back.gif){kind=icon}
Return to btreeInt.h CVS log ![[TXT]](/icons/cvsweb/text.gif){kind=icon}
![[DIR]](/icons/cvsweb/dir.gif){kind=icon}
Up to [ELWIX - Embedded LightWeight unIX -] / embedaddon / sqlite3 / src