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** 2008 August 05
** The author disclaims copyright to this source code. In place of
** a legal notice, here is a blessing:
** May you do good and not evil.
** May you find forgiveness for yourself and forgive others.
** May you share freely, never taking more than you give.
** This header file defines the interface that the sqlite page cache
** subsystem.
#ifndef _PCACHE_H_
typedef struct PgHdr PgHdr;
typedef struct PCache PCache;
** Every page in the cache is controlled by an instance of the following
** structure.
struct PgHdr {
void *pData; /* Content of this page */
void *pExtra; /* Extra content */
PgHdr *pDirty; /* Transient list of dirty pages */
Pgno pgno; /* Page number for this page */
Pager *pPager; /* The pager this page is part of */
u32 pageHash; /* Hash of page content */
u16 flags; /* PGHDR flags defined below */
** Elements above are public. All that follows is private to pcache.c
** and should not be accessed by other modules.
i16 nRef; /* Number of users of this page */
PCache *pCache; /* Cache that owns this page */
PgHdr *pDirtyNext; /* Next element in list of dirty pages */
PgHdr *pDirtyPrev; /* Previous element in list of dirty pages */
/* Bit values for PgHdr.flags */
#define PGHDR_DIRTY 0x002 /* Page has changed */
#define PGHDR_NEED_SYNC 0x004 /* Fsync the rollback journal before
** writing this page to the database */
#define PGHDR_NEED_READ 0x008 /* Content is unread */
#define PGHDR_REUSE_UNLIKELY 0x010 /* A hint that reuse is unlikely */
#define PGHDR_DONT_WRITE 0x020 /* Do not write content to disk */
/* Initialize and shutdown the page cache subsystem */
int sqlite3PcacheInitialize(void);
void sqlite3PcacheShutdown(void);
/* Page cache buffer management:
** These routines implement SQLITE_CONFIG_PAGECACHE.
void sqlite3PCacheBufferSetup(void *, int sz, int n);
/* Create a new pager cache.
** Under memory stress, invoke xStress to try to make pages clean.
** Only clean and unpinned pages can be reclaimed.
void sqlite3PcacheOpen(
int szPage, /* Size of every page */
int szExtra, /* Extra space associated with each page */
int bPurgeable, /* True if pages are on backing store */
int (*xStress)(void*, PgHdr*), /* Call to try to make pages clean */
void *pStress, /* Argument to xStress */
PCache *pToInit /* Preallocated space for the PCache */
/* Modify the page-size after the cache has been created. */
void sqlite3PcacheSetPageSize(PCache *, int);
/* Return the size in bytes of a PCache object. Used to preallocate
** storage space.
int sqlite3PcacheSize(void);
/* One release per successful fetch. Page is pinned until released.
** Reference counted.
int sqlite3PcacheFetch(PCache*, Pgno, int createFlag, PgHdr**);
void sqlite3PcacheRelease(PgHdr*);
void sqlite3PcacheDrop(PgHdr*); /* Remove page from cache */
void sqlite3PcacheMakeDirty(PgHdr*); /* Make sure page is marked dirty */
void sqlite3PcacheMakeClean(PgHdr*); /* Mark a single page as clean */
void sqlite3PcacheCleanAll(PCache*); /* Mark all dirty list pages as clean */
/* Change a page number. Used by incr-vacuum. */
void sqlite3PcacheMove(PgHdr*, Pgno);
/* Remove all pages with pgno>x. Reset the cache if x==0 */
void sqlite3PcacheTruncate(PCache*, Pgno x);
/* Get a list of all dirty pages in the cache, sorted by page number */
PgHdr *sqlite3PcacheDirtyList(PCache*);
/* Reset and close the cache object */
void sqlite3PcacheClose(PCache*);
/* Clear flags from pages of the page cache */
void sqlite3PcacheClearSyncFlags(PCache *);
/* Discard the contents of the cache */
void sqlite3PcacheClear(PCache*);
/* Return the total number of outstanding page references */
int sqlite3PcacheRefCount(PCache*);
/* Increment the reference count of an existing page */
void sqlite3PcacheRef(PgHdr*);
int sqlite3PcachePageRefcount(PgHdr*);
/* Return the total number of pages stored in the cache */
int sqlite3PcachePagecount(PCache*);
#if defined(SQLITE_CHECK_PAGES) || defined(SQLITE_DEBUG)
/* Iterate through all dirty pages currently stored in the cache. This
** interface is only available if SQLITE_CHECK_PAGES is defined when the
** library is built.
void sqlite3PcacheIterateDirty(PCache *pCache, void (*xIter)(PgHdr *));
/* Set and get the suggested cache-size for the specified pager-cache.
** If no global maximum is configured, then the system attempts to limit
** the total number of pages cached by purgeable pager-caches to the sum
** of the suggested cache-sizes.
void sqlite3PcacheSetCachesize(PCache *, int);
int sqlite3PcacheGetCachesize(PCache *);
/* Try to return memory used by the pcache module to the main memory heap */
int sqlite3PcacheReleaseMemory(int);
void sqlite3PcacheStats(int*,int*,int*,int*);
void sqlite3PCacheSetDefault(void);
#endif /* _PCACHE_H_ */