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Overview
Comment: | Further refinements to the virtual method implementation of sqlite3PagerGet(). |
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Downloads: | Tarball | ZIP archive |
Timelines: | family | ancestors | descendants | both | pager-get-method |
Files: | files | file ages | folders |
SHA1: |
67df44464847b43f8c0b186157e31cc6 |
User & Date: | drh 2016-12-13 15:53:22.192 |
Context
2016-12-13
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18:34 | In the pager, avoid checking for the illegal page number 0 except when creating a new page. (Closed-Leaf check-in: dee20ba982 user: drh tags: pager-get-method) | |
15:53 | Further refinements to the virtual method implementation of sqlite3PagerGet(). (check-in: 67df444648 user: drh tags: pager-get-method) | |
14:32 | Make the sqlite3PagerGet() interface into a virtual method, with different implementations based on the current state of the pager. This gives a small performance increase by avoiding unnecessary branches inside the various methods. (check-in: df5bb90d20 user: drh tags: pager-get-method) | |
Changes
Changes to src/pager.c.
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1018 1019 1020 1021 1022 1023 1024 | return zRet; } #endif /* Forward references to the various page getters */ static int getPageNormal(Pager*,Pgno,DbPage**,int); | | > | > > > | 1018 1019 1020 1021 1022 1023 1024 1025 1026 1027 1028 1029 1030 1031 1032 1033 1034 1035 1036 1037 1038 1039 1040 1041 1042 1043 1044 1045 1046 1047 1048 1049 1050 1051 | return zRet; } #endif /* Forward references to the various page getters */ static int getPageNormal(Pager*,Pgno,DbPage**,int); static int getPageError(Pager*,Pgno,DbPage**,int); #if SQLITE_MAX_MMAP_SIZE>0 static int getPageMMap(Pager*,Pgno,DbPage**,int); #endif /* ** Set the Pager.xGet method for the appropriate routine used to fetch ** content from the pager. */ static void setGetterMethod(Pager *pPager){ if( pPager->errCode ){ pPager->xGet = getPageError; #if SQLITE_MAX_MMAP_SIZE>0 }else if( USEFETCH(pPager) #ifdef SQLITE_HAS_CODEC && pPager->xCodec==0 #endif ){ pPager->xGet = getPageMMap; #endif /* SQLITE_MAX_MMAP_SIZE>0 */ }else{ pPager->xGet = getPageNormal; } } /* ** Return true if it is necessary to write page *pPg into the sub-journal. |
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5291 5292 5293 5294 5295 5296 5297 | static void pagerUnlockIfUnused(Pager *pPager){ if( pPager->nMmapOut==0 && (sqlite3PcacheRefCount(pPager->pPCache)==0) ){ pagerUnlockAndRollback(pPager); } } /* | | | > > > > > > > | | | | | | | 5295 5296 5297 5298 5299 5300 5301 5302 5303 5304 5305 5306 5307 5308 5309 5310 5311 5312 5313 5314 5315 5316 5317 5318 5319 5320 5321 5322 5323 5324 5325 5326 5327 5328 5329 5330 5331 5332 5333 5334 5335 5336 5337 5338 5339 5340 5341 5342 5343 5344 5345 5346 5347 | static void pagerUnlockIfUnused(Pager *pPager){ if( pPager->nMmapOut==0 && (sqlite3PcacheRefCount(pPager->pPCache)==0) ){ pagerUnlockAndRollback(pPager); } } /* ** The page getter methods each try to acquire a reference to a ** page with page number pgno. If the requested reference is ** successfully obtained, it is copied to *ppPage and SQLITE_OK returned. ** ** There are different implementations of the getter method depending ** on the current state of the pager. ** ** getPageNormal() -- The normal getter ** getPageError() -- Used if the pager is in an error state ** getPageMmap() -- Used if memory-mapped I/O is enabled ** ** If the requested page is already in the cache, it is returned. ** Otherwise, a new page object is allocated and populated with data ** read from the database file. In some cases, the pcache module may ** choose not to allocate a new page object and may reuse an existing ** object with no outstanding references. ** ** The extra data appended to a page is always initialized to zeros the ** first time a page is loaded into memory. If the page requested is ** already in the cache when this function is called, then the extra ** data is left as it was when the page object was last used. ** ** If the database image is smaller than the requested page or if ** the flags parameter contains the PAGER_GET_NOCONTENT bit and the ** requested page is not already stored in the cache, then no ** actual disk read occurs. In this case the memory image of the ** page is initialized to all zeros. ** ** If PAGER_GET_NOCONTENT is true, it means that we do not care about ** the contents of the page. This occurs in two scenarios: ** ** a) When reading a free-list leaf page from the database, and ** ** b) When a savepoint is being rolled back and we need to load ** a new page into the cache to be filled with the data read ** from the savepoint journal. ** ** If PAGER_GET_NOCONTENT is true, then the data returned is zeroed instead ** of being read from the database. Additionally, the bits corresponding ** to pgno in Pager.pInJournal (bitvec of pages already written to the ** journal file) and the PagerSavepoint.pInSavepoint bitvecs of any open ** savepoints are set. This means if the page is made writable at any ** point in the future, using a call to sqlite3PagerWrite(), its contents ** will not be journaled. This saves IO. ** ** The acquisition might fail for several reasons. In all cases, |
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5347 5348 5349 5350 5351 5352 5353 | static int getPageNormal( Pager *pPager, /* The pager open on the database file */ Pgno pgno, /* Page number to fetch */ DbPage **ppPage, /* Write a pointer to the page here */ int flags /* PAGER_GET_XXX flags */ ){ int rc = SQLITE_OK; | | < | > < | > | 5358 5359 5360 5361 5362 5363 5364 5365 5366 5367 5368 5369 5370 5371 5372 5373 5374 5375 5376 5377 5378 5379 5380 5381 5382 5383 5384 5385 5386 5387 5388 5389 5390 5391 5392 5393 5394 5395 5396 5397 5398 5399 5400 5401 5402 5403 5404 5405 5406 5407 5408 5409 5410 5411 5412 5413 5414 5415 5416 5417 5418 5419 5420 5421 | static int getPageNormal( Pager *pPager, /* The pager open on the database file */ Pgno pgno, /* Page number to fetch */ DbPage **ppPage, /* Write a pointer to the page here */ int flags /* PAGER_GET_XXX flags */ ){ int rc = SQLITE_OK; PgHdr *pPg; u8 noContent; /* True if PAGER_GET_NOCONTENT is set */ sqlite3_pcache_page *pBase; if( pgno==0 ){ return SQLITE_CORRUPT_BKPT; } assert( pPager->errCode==SQLITE_OK ); assert( pPager->eState>=PAGER_READER ); assert( assert_pager_state(pPager) ); assert( pPager->hasHeldSharedLock==1 ); pBase = sqlite3PcacheFetch(pPager->pPCache, pgno, 3); if( pBase==0 ){ pPg = 0; rc = sqlite3PcacheFetchStress(pPager->pPCache, pgno, &pBase); if( rc!=SQLITE_OK ) goto pager_acquire_err; if( pBase==0 ){ rc = SQLITE_NOMEM_BKPT; goto pager_acquire_err; } } pPg = *ppPage = sqlite3PcacheFetchFinish(pPager->pPCache, pgno, pBase); assert( pPg==(*ppPage) ); assert( pPg->pgno==pgno ); assert( pPg->pPager==pPager || pPg->pPager==0 ); if( pPg->pPager ){ /* In this case the pcache already contains an initialized copy of ** the page. Return without further ado. */ assert( pgno<=PAGER_MAX_PGNO && pgno!=PAGER_MJ_PGNO(pPager) ); pPager->aStat[PAGER_STAT_HIT]++; return SQLITE_OK; }else{ /* The pager cache has created a new page. Its content needs to ** be initialized. */ pPg->pPager = pPager; /* The maximum page number is 2^31. Return SQLITE_CORRUPT if a page ** number greater than this, or the unused locking-page, is requested. */ if( pgno>PAGER_MAX_PGNO || pgno==PAGER_MJ_PGNO(pPager) ){ rc = SQLITE_CORRUPT_BKPT; goto pager_acquire_err; } assert( !isOpen(pPager->fd) || !MEMDB ); noContent = (flags & PAGER_GET_NOCONTENT)!=0; if( !isOpen(pPager->fd) || pPager->dbSize<pgno || noContent ){ if( pgno>pPager->mxPgno ){ rc = SQLITE_FULL; goto pager_acquire_err; } if( noContent ){ /* Failure to set the bits in the InJournal bit-vectors is benign. |
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5421 5422 5423 5424 5425 5426 5427 | TESTONLY( rc = ) addToSavepointBitvecs(pPager, pgno); testcase( rc==SQLITE_NOMEM ); sqlite3EndBenignMalloc(); } memset(pPg->pData, 0, pPager->pageSize); IOTRACE(("ZERO %p %d\n", pPager, pgno)); }else{ | > | | 5432 5433 5434 5435 5436 5437 5438 5439 5440 5441 5442 5443 5444 5445 5446 5447 | TESTONLY( rc = ) addToSavepointBitvecs(pPager, pgno); testcase( rc==SQLITE_NOMEM ); sqlite3EndBenignMalloc(); } memset(pPg->pData, 0, pPager->pageSize); IOTRACE(("ZERO %p %d\n", pPager, pgno)); }else{ u32 iFrame = 0; /* Frame to read from WAL file */ if( pagerUseWal(pPager) ){ rc = sqlite3WalFindFrame(pPager->pWal, pgno, &iFrame); if( rc!=SQLITE_OK ) goto pager_acquire_err; } assert( pPg->pPager==pPager ); pPager->aStat[PAGER_STAT_MISS]++; rc = readDbPage(pPg, iFrame); if( rc!=SQLITE_OK ){ |
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5446 5447 5448 5449 5450 5451 5452 5453 5454 5455 5456 5457 5458 5459 | sqlite3PcacheDrop(pPg); } pagerUnlockIfUnused(pPager); *ppPage = 0; return rc; } /* The page getter for when memory-mapped I/O is enabled */ static int getPageMMap( Pager *pPager, /* The pager open on the database file */ Pgno pgno, /* Page number to fetch */ DbPage **ppPage, /* Write a pointer to the page here */ int flags /* PAGER_GET_XXX flags */ ){ | > | 5458 5459 5460 5461 5462 5463 5464 5465 5466 5467 5468 5469 5470 5471 5472 | sqlite3PcacheDrop(pPg); } pagerUnlockIfUnused(pPager); *ppPage = 0; return rc; } #if SQLITE_MAX_MMAP_SIZE>0 /* The page getter for when memory-mapped I/O is enabled */ static int getPageMMap( Pager *pPager, /* The pager open on the database file */ Pgno pgno, /* Page number to fetch */ DbPage **ppPage, /* Write a pointer to the page here */ int flags /* PAGER_GET_XXX flags */ ){ |
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5516 5517 5518 5519 5520 5521 5522 5523 5524 5525 5526 5527 5528 5529 | if( rc!=SQLITE_OK ){ *ppPage = 0; return rc; } } return getPageNormal(pPager, pgno, ppPage, flags); } /* The page getter method for when the pager is an error state */ static int getPageError( Pager *pPager, /* The pager open on the database file */ Pgno pgno, /* Page number to fetch */ DbPage **ppPage, /* Write a pointer to the page here */ int flags /* PAGER_GET_XXX flags */ | > | 5529 5530 5531 5532 5533 5534 5535 5536 5537 5538 5539 5540 5541 5542 5543 | if( rc!=SQLITE_OK ){ *ppPage = 0; return rc; } } return getPageNormal(pPager, pgno, ppPage, flags); } #endif /* SQLITE_MAX_MMAP_SIZE>0 */ /* The page getter method for when the pager is an error state */ static int getPageError( Pager *pPager, /* The pager open on the database file */ Pgno pgno, /* Page number to fetch */ DbPage **ppPage, /* Write a pointer to the page here */ int flags /* PAGER_GET_XXX flags */ |
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