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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.
**
** @(#) $Id: pcache.h,v 1.6 2008/08/26 18:05:48 danielk1977 Exp $
*/
#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 {
u32 flags; /* PGHDR flags defined below */
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;
#ifdef SQLITE_CHECK_PAGES
u32 pageHash;
#endif
/*** Public data is above. All that follows is private to pcache.c ***/
PCache *pCache; /* Cache that owns this page */
PgHdr *pNextHash, *pPrevHash; /* Hash collision chain for PgHdr.pgno */
PgHdr *pNext, *pPrev; /* List of clean or dirty pages */
PgHdr *pNextLru, *pPrevLru; /* Part of global LRU list */
int nRef; /* Number of users of this page */
void *apSave[2]; /* Journal entries for in-memory databases */
};
/* Bit values for PgHdr.flags */
#define PGHDR_IN_JOURNAL 0x001 /* Page is in rollback journal */
#define PGHDR_IN_STMTJRNL 0x002 /* Page is in the statement journal */
#define PGHDR_DIRTY 0x004 /* Page has changed */
#define PGHDR_NEED_SYNC 0x008 /* Peed to fsync this page */
#define PGHDR_ALWAYS_ROLLBACK 0x010 /* Force writing to journal */
#define PGHDR_NEED_READ 0x020 /* Content is unread */
#define PGHDR_IS_INIT 0x040 /* pData is initialized */
#define PGHDR_REUSE_UNLIKELY 0x080 /* Hint: Reuse is unlikely */
#define PGHDR_DONT_WRITE 0x100 /* 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);
void *sqlite3PCacheMalloc(int sz);
void sqlite3PCacheFree(void*);
/* 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 */
void (*xDestroy)(PgHdr *), /* Called to destroy a page */
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);
/* Routines used to implement transactions on memory-only databases. */
int sqlite3PcachePreserve(PgHdr*, int); /* Preserve current page content */
void sqlite3PcacheCommit(PCache*, int); /* Drop preserved copy */
void sqlite3PcacheRollback(PCache*, int); /* Rollback to preserved copy */
/* 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*);
/* Set flags on all pages in the page cache */
void sqlite3PcacheSetFlags(PCache*, int andMask, int orMask);
/* Assert flags settings on all pages. Debugging only */
void sqlite3PcacheAssertFlags(PCache*, int trueMask, int falseMask);
/* Return true if the number of dirty pages is 0 or 1 */
int sqlite3PcacheZeroOrOneDirtyPages(PCache*);
/* Discard the contents of the cache */
int sqlite3PcacheClear(PCache*);
/* Return the total number of outstanding page references */
int sqlite3PcacheRefCount(PCache*);
/* Increment the reference count of an existing page */
void sqlite3PcacheRef(PgHdr*);
/* Return the total number of pages stored in the cache */
int sqlite3PcachePagecount(PCache*);
/* Iterate through all pages currently stored in the cache. This interface
** is only available if SQLITE_CHECK_PAGES is defined when the library is
** built.
*/
void sqlite3PcacheIterate(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.
*/
int sqlite3PcacheGetCachesize(PCache *);
void sqlite3PcacheSetCachesize(PCache *, int);
/* Try to return memory used by the pcache module to the main memory heap */
int sqlite3PcacheReleaseMemory(int);
#endif /* _PCACHE_H_ */
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