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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.
11 *************************************************************************
12 ** This header file defines the interface that the sqlite page cache
13 ** subsystem.
16 #ifndef _PCACHE_H_
18 typedef struct PgHdr PgHdr;
19 typedef struct PCache PCache;
22 ** Every page in the cache is controlled by an instance of the following
23 ** structure.
25 struct PgHdr {
26 sqlite3_pcache_page *pPage; /* Pcache object page handle */
27 void *pData; /* Page data */
28 void *pExtra; /* Extra content */
29 PgHdr *pDirty; /* Transient list of dirty pages */
30 Pager *pPager; /* The pager this page is part of */
31 Pgno pgno; /* Page number for this page */
32 #ifdef SQLITE_CHECK_PAGES
33 u32 pageHash; /* Hash of page content */
34 #endif
35 u16 flags; /* PGHDR flags defined below */
37 /**********************************************************************
38 ** Elements above are public. All that follows is private to pcache.c
39 ** and should not be accessed by other modules.
41 i16 nRef; /* Number of users of this page */
42 PCache *pCache; /* Cache that owns this page */
44 PgHdr *pDirtyNext; /* Next element in list of dirty pages */
45 PgHdr *pDirtyPrev; /* Previous element in list of dirty pages */
48 /* Bit values for PgHdr.flags */
49 #define PGHDR_DIRTY 0x002 /* Page has changed */
50 #define PGHDR_NEED_SYNC 0x004 /* Fsync the rollback journal before
51 ** writing this page to the database */
52 #define PGHDR_NEED_READ 0x008 /* Content is unread */
53 #define PGHDR_REUSE_UNLIKELY 0x010 /* A hint that reuse is unlikely */
54 #define PGHDR_DONT_WRITE 0x020 /* Do not write content to disk */
56 #define PGHDR_MMAP 0x040 /* This is an mmap page object */
58 /* Initialize and shutdown the page cache subsystem */
59 int sqlite3PcacheInitialize(void);
60 void sqlite3PcacheShutdown(void);
62 /* Page cache buffer management:
63 ** These routines implement SQLITE_CONFIG_PAGECACHE.
65 void sqlite3PCacheBufferSetup(void *, int sz, int n);
67 /* Create a new pager cache.
68 ** Under memory stress, invoke xStress to try to make pages clean.
69 ** Only clean and unpinned pages can be reclaimed.
71 int sqlite3PcacheOpen(
72 int szPage, /* Size of every page */
73 int szExtra, /* Extra space associated with each page */
74 int bPurgeable, /* True if pages are on backing store */
75 int (*xStress)(void*, PgHdr*), /* Call to try to make pages clean */
76 void *pStress, /* Argument to xStress */
77 PCache *pToInit /* Preallocated space for the PCache */
80 /* Modify the page-size after the cache has been created. */
81 int sqlite3PcacheSetPageSize(PCache *, int);
83 /* Return the size in bytes of a PCache object. Used to preallocate
84 ** storage space.
86 int sqlite3PcacheSize(void);
88 /* One release per successful fetch. Page is pinned until released.
89 ** Reference counted.
91 sqlite3_pcache_page *sqlite3PcacheFetch(PCache*, Pgno, int createFlag);
92 int sqlite3PcacheFetchStress(PCache*, Pgno, sqlite3_pcache_page**);
93 PgHdr *sqlite3PcacheFetchFinish(PCache*, Pgno, sqlite3_pcache_page *pPage);
94 void sqlite3PcacheRelease(PgHdr*);
96 void sqlite3PcacheDrop(PgHdr*); /* Remove page from cache */
97 void sqlite3PcacheMakeDirty(PgHdr*); /* Make sure page is marked dirty */
98 void sqlite3PcacheMakeClean(PgHdr*); /* Mark a single page as clean */
99 void sqlite3PcacheCleanAll(PCache*); /* Mark all dirty list pages as clean */
101 /* Change a page number. Used by incr-vacuum. */
102 void sqlite3PcacheMove(PgHdr*, Pgno);
104 /* Remove all pages with pgno>x. Reset the cache if x==0 */
105 void sqlite3PcacheTruncate(PCache*, Pgno x);
107 /* Get a list of all dirty pages in the cache, sorted by page number */
108 PgHdr *sqlite3PcacheDirtyList(PCache*);
110 /* Reset and close the cache object */
111 void sqlite3PcacheClose(PCache*);
113 /* Clear flags from pages of the page cache */
114 void sqlite3PcacheClearSyncFlags(PCache *);
116 /* Discard the contents of the cache */
117 void sqlite3PcacheClear(PCache*);
119 /* Return the total number of outstanding page references */
120 int sqlite3PcacheRefCount(PCache*);
122 /* Increment the reference count of an existing page */
123 void sqlite3PcacheRef(PgHdr*);
125 int sqlite3PcachePageRefcount(PgHdr*);
127 /* Return the total number of pages stored in the cache */
128 int sqlite3PcachePagecount(PCache*);
130 #if defined(SQLITE_CHECK_PAGES) || defined(SQLITE_DEBUG)
131 /* Iterate through all dirty pages currently stored in the cache. This
132 ** interface is only available if SQLITE_CHECK_PAGES is defined when the
133 ** library is built.
135 void sqlite3PcacheIterateDirty(PCache *pCache, void (*xIter)(PgHdr *));
136 #endif
138 /* Set and get the suggested cache-size for the specified pager-cache.
140 ** If no global maximum is configured, then the system attempts to limit
141 ** the total number of pages cached by purgeable pager-caches to the sum
142 ** of the suggested cache-sizes.
144 void sqlite3PcacheSetCachesize(PCache *, int);
145 #ifdef SQLITE_TEST
146 int sqlite3PcacheGetCachesize(PCache *);
147 #endif
149 /* Free up as much memory as possible from the page cache */
150 void sqlite3PcacheShrink(PCache*);
152 #ifdef SQLITE_ENABLE_MEMORY_MANAGEMENT
153 /* Try to return memory used by the pcache module to the main memory heap */
154 int sqlite3PcacheReleaseMemory(int);
155 #endif
157 #ifdef SQLITE_TEST
158 void sqlite3PcacheStats(int*,int*,int*,int*);
159 #endif
161 void sqlite3PCacheSetDefault(void);
163 #endif /* _PCACHE_H_ */