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Overview
Comment: | Update some comments in wal.c. No code changes. |
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SHA1: |
1ce9c92bffa5d7f8431c005b29d698b0 |
User & Date: | dan 2010-06-14 11:49:26.000 |
Context
2010-06-14
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14:07 | Remove xShmGet/Size/Release from the sqlite3_vfs structure. Change the name of xShmPage to xShmMap. Remove some code that is now unused from os_unix.c and some of the test VFS implementations. (check-in: fc0cabc15c user: dan tags: experimental) | |
11:49 | Update some comments in wal.c. No code changes. (check-in: 1ce9c92bff user: dan tags: experimental) | |
11:18 | Change the interface to internal function walGetHash() to make it easier to follow. (check-in: 5e8e2e978e user: dan tags: experimental) | |
Changes
Changes to src/wal.c.
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137 138 139 140 141 142 143 | ** a page number P, return the index of the last frame for page P in the WAL, ** or return NULL if there are no frames for page P in the WAL. ** ** The wal-index consists of a header region, followed by an one or ** more index blocks. ** ** The wal-index header contains the total number of frames within the WAL | | > > > > > > > > | | | | | | > | > > > | > | | < | | 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 | ** a page number P, return the index of the last frame for page P in the WAL, ** or return NULL if there are no frames for page P in the WAL. ** ** The wal-index consists of a header region, followed by an one or ** more index blocks. ** ** The wal-index header contains the total number of frames within the WAL ** in the the mxFrame field. ** ** Each index block except for the first contains information on ** HASHTABLE_NPAGE frames. The first index block contains information on ** HASHTABLE_NPAGE_ONE frames. The values of HASHTABLE_NPAGE_ONE and ** HASHTABLE_NPAGE are selected so that together the wal-index header and ** first index block are the same size as all other index blocks in the ** wal-index. ** ** Each index block contains two sections, a page-mapping that contains the ** database page number associated with each wal frame, and a hash-table ** that allows users to query an index block for a specific page number. ** The page-mapping is an array of HASHTABLE_NPAGE (or HASHTABLE_NPAGE_ONE ** for the first index block) 32-bit page numbers. The first entry in the ** first index-block contains the database page number corresponding to the ** first frame in the WAL file. The first entry in the second index block ** in the WAL file corresponds to the (HASHTABLE_NPAGE_ONE+1)th frame in ** the log, and so on. ** ** The last index block in a wal-index usually contains less than the full ** complement of HASHTABLE_NPAGE (or HASHTABLE_NPAGE_ONE) page-numbers, ** depending on the contents of the WAL file. This does not change the ** allocated size of the page-mapping array - the page-mapping array merely ** contains unused entries. ** ** Even without using the hash table, the last frame for page P ** can be found by scanning the page-mapping sections of each index block ** starting with the last index block and moving toward the first, and ** within each index block, starting at the end and moving toward the ** beginning. The first entry that equals P corresponds to the frame ** holding the content for that page. ** ** The hash table consists of HASHTABLE_NSLOT 16-bit unsigned integers. ** HASHTABLE_NSLOT = 2*HASHTABLE_NPAGE, and there is one entry in the |
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388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 | /* ** Each page of the wal-index mapping contains a hash-table made up of ** an array of HASHTABLE_NSLOT elements of the following type. */ typedef u16 ht_slot; /* ** Define the parameters of the hash tables in the wal-index file. There ** is a hash-table following every HASHTABLE_NPAGE page numbers in the ** wal-index. ** ** Changing any of these constants will alter the wal-index format and ** create incompatibilities. */ #define HASHTABLE_NPAGE 4096 /* Must be power of 2 */ #define HASHTABLE_HASH_1 383 /* Should be prime */ #define HASHTABLE_NSLOT (HASHTABLE_NPAGE*2) /* Must be a power of 2 */ | > > > > > > > > > > > > > > > > > > > > > > > > > > > > | | 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 | /* ** Each page of the wal-index mapping contains a hash-table made up of ** an array of HASHTABLE_NSLOT elements of the following type. */ typedef u16 ht_slot; /* ** This structure is used to implement an iterator that loops through ** all frames in the WAL in database page order. Where two or more frames ** correspond to the same database page, the iterator visits only the ** frame most recently written to the WAL (in other words, the frame with ** the largest index). ** ** The internals of this structure are only accessed by: ** ** walIteratorInit() - Create a new iterator, ** walIteratorNext() - Step an iterator, ** walIteratorFree() - Free an iterator. ** ** This functionality is used by the checkpoint code (see walCheckpoint()). */ struct WalIterator { int iPrior; /* Last result returned from the iterator */ int nSegment; /* Size of the aSegment[] array */ struct WalSegment { int iNext; /* Next slot in aIndex[] not yet returned */ ht_slot *aIndex; /* i0, i1, i2... such that aPgno[iN] ascend */ u32 *aPgno; /* Array of page numbers. */ int nEntry; /* Max size of aPgno[] and aIndex[] arrays */ int iZero; /* Frame number associated with aPgno[0] */ } aSegment[1]; /* One for every 32KB page in the WAL */ }; /* ** Define the parameters of the hash tables in the wal-index file. There ** is a hash-table following every HASHTABLE_NPAGE page numbers in the ** wal-index. ** ** Changing any of these constants will alter the wal-index format and ** create incompatibilities. */ #define HASHTABLE_NPAGE 4096 /* Must be power of 2 */ #define HASHTABLE_HASH_1 383 /* Should be prime */ #define HASHTABLE_NSLOT (HASHTABLE_NPAGE*2) /* Must be a power of 2 */ /* ** The block of page numbers associated with the first hash-table in a ** wal-index is smaller than usual. This is so that there is a complete ** hash-table on each aligned 32KB page of the wal-index. */ #define HASHTABLE_NPAGE_ONE (HASHTABLE_NPAGE - (WALINDEX_HDR_SIZE/sizeof(u32))) /* The wal-index is divided into pages of WALINDEX_PGSZ bytes each. */ #define WALINDEX_PGSZ ( \ |
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465 466 467 468 469 470 471 | ** Return a pointer to the WalIndexHdr structure in the wal-index. */ static volatile WalIndexHdr *walIndexHdr(Wal *pWal){ assert( pWal->nWiData>0 && pWal->apWiData[0] ); return (volatile WalIndexHdr*)pWal->apWiData[0]; } | < < < < < < < < < < < < < < < < < < < < < < < < < < < | 505 506 507 508 509 510 511 512 513 514 515 516 517 518 | ** Return a pointer to the WalIndexHdr structure in the wal-index. */ static volatile WalIndexHdr *walIndexHdr(Wal *pWal){ assert( pWal->nWiData>0 && pWal->apWiData[0] ); return (volatile WalIndexHdr*)pWal->apWiData[0]; } /* ** The argument to this macro must be of type u32. On a little-endian ** architecture, it returns the u32 value that results from interpreting ** the 4 bytes as a big-endian value. On a big-endian architecture, it ** returns the value that would be produced by intepreting the 4 bytes ** of the input value as a little-endian integer. */ |
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