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