1 /* 2 ** 2008 August 05 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 header file defines the interface that the sqlite page cache 13 ** subsystem. 14 ** 15 ** @(#) $Id: pcache.h,v 1.15 2008/11/13 14:28:29 danielk1977 Exp $ 16 */ 17 18 #ifndef _PCACHE_H_ 19 20 typedef struct PgHdr PgHdr; 21 typedef struct PCache PCache; 22 23 /* 24 ** Every page in the cache is controlled by an instance of the following 25 ** structure. 26 */ 27 struct PgHdr { 28 void *pData; /* Content of this page */ 29 void *pExtra; /* Extra content */ 30 PgHdr *pDirty; /* Transient list of dirty pages */ 31 Pgno pgno; /* Page number for this page */ 32 Pager *pPager; /* The pager this page is part of */ 33 #ifdef SQLITE_CHECK_PAGES 34 u32 pageHash; /* Hash of page content */ 35 #endif 36 u16 flags; /* PGHDR flags defined below */ 37 38 /********************************************************************** 39 ** Elements above are public. All that follows is private to pcache.c 40 ** and should not be accessed by other modules. 41 */ 42 i16 nRef; /* Number of users of this page */ 43 PCache *pCache; /* Cache that owns this page */ 44 45 PgHdr *pDirtyNext; /* Next element in list of dirty pages */ 46 PgHdr *pDirtyPrev; /* Previous element in list of dirty pages */ 47 }; 48 49 /* Bit values for PgHdr.flags */ 50 #define PGHDR_DIRTY 0x002 /* Page has changed */ 51 #define PGHDR_NEED_SYNC 0x004 /* Fsync the rollback journal before 52 ** writing this page to the database */ 53 #define PGHDR_NEED_READ 0x008 /* Content is unread */ 54 #define PGHDR_REUSE_UNLIKELY 0x010 /* A hint that reuse is unlikely */ 55 #define PGHDR_DONT_WRITE 0x020 /* Do not write content to disk */ 56 57 /* Initialize and shutdown the page cache subsystem */ 58 int sqlite3PcacheInitialize(void); 59 void sqlite3PcacheShutdown(void); 60 61 /* Page cache buffer management: 62 ** These routines implement SQLITE_CONFIG_PAGECACHE. 63 */ 64 void sqlite3PCacheBufferSetup(void *, int sz, int n); 65 void *sqlite3PCacheMalloc(int sz); 66 void sqlite3PCacheFree(void*); 67 68 /* Create a new pager cache. 69 ** Under memory stress, invoke xStress to try to make pages clean. 70 ** Only clean and unpinned pages can be reclaimed. 71 */ 72 void sqlite3PcacheOpen( 73 int szPage, /* Size of every page */ 74 int szExtra, /* Extra space associated with each page */ 75 int bPurgeable, /* True if pages are on backing store */ 76 int (*xStress)(void*, PgHdr*), /* Call to try to make pages clean */ 77 void *pStress, /* Argument to xStress */ 78 PCache *pToInit /* Preallocated space for the PCache */ 79 ); 80 81 /* Modify the page-size after the cache has been created. */ 82 void sqlite3PcacheSetPageSize(PCache *, int); 83 84 /* Return the size in bytes of a PCache object. Used to preallocate 85 ** storage space. 86 */ 87 int sqlite3PcacheSize(void); 88 89 /* One release per successful fetch. Page is pinned until released. 90 ** Reference counted. 91 */ 92 int sqlite3PcacheFetch(PCache*, Pgno, int createFlag, PgHdr**); 93 void sqlite3PcacheRelease(PgHdr*); 94 95 void sqlite3PcacheDrop(PgHdr*); /* Remove page from cache */ 96 void sqlite3PcacheMakeDirty(PgHdr*); /* Make sure page is marked dirty */ 97 void sqlite3PcacheMakeClean(PgHdr*); /* Mark a single page as clean */ 98 void sqlite3PcacheCleanAll(PCache*); /* Mark all dirty list pages as clean */ 99 100 /* Change a page number. Used by incr-vacuum. */ 101 void sqlite3PcacheMove(PgHdr*, Pgno); 102 103 /* Remove all pages with pgno>x. Reset the cache if x==0 */ 104 void sqlite3PcacheTruncate(PCache*, Pgno x); 105 106 /* Get a list of all dirty pages in the cache, sorted by page number */ 107 PgHdr *sqlite3PcacheDirtyList(PCache*); 108 109 /* Reset and close the cache object */ 110 void sqlite3PcacheClose(PCache*); 111 112 /* Clear flags from pages of the page cache */ 113 void sqlite3PcacheClearSyncFlags(PCache *); 114 115 /* Return true if the number of dirty pages is 0 or 1 */ 116 int sqlite3PcacheZeroOrOneDirtyPages(PCache*); 117 118 /* Discard the contents of the cache */ 119 int sqlite3PcacheClear(PCache*); 120 121 /* Return the total number of outstanding page references */ 122 int sqlite3PcacheRefCount(PCache*); 123 124 /* Increment the reference count of an existing page */ 125 void sqlite3PcacheRef(PgHdr*); 126 127 int sqlite3PcachePageRefcount(PgHdr*); 128 129 /* Return the total number of pages stored in the cache */ 130 int sqlite3PcachePagecount(PCache*); 131 132 #ifdef SQLITE_CHECK_PAGES 133 /* Iterate through all dirty pages currently stored in the cache. This 134 ** interface is only available if SQLITE_CHECK_PAGES is defined when the 135 ** library is built. 136 */ 137 void sqlite3PcacheIterateDirty(PCache *pCache, void (*xIter)(PgHdr *)); 138 #endif 139 140 /* Set and get the suggested cache-size for the specified pager-cache. 141 ** 142 ** If no global maximum is configured, then the system attempts to limit 143 ** the total number of pages cached by purgeable pager-caches to the sum 144 ** of the suggested cache-sizes. 145 */ 146 int sqlite3PcacheGetCachesize(PCache *); 147 void sqlite3PcacheSetCachesize(PCache *, int); 148 149 #ifdef SQLITE_ENABLE_MEMORY_MANAGEMENT 150 /* Try to return memory used by the pcache module to the main memory heap */ 151 int sqlite3PcacheReleaseMemory(int); 152 #endif 153 154 #ifdef SQLITE_TEST 155 void sqlite3PcacheStats(int*,int*,int*,int*); 156 #endif 157 158 void sqlite3PCacheSetDefault(void); 159 160 #endif /* _PCACHE_H_ */ 161