sqlite3_pcache *pCache;             /* Pluggable cache module */
};

/*
** Debug tracing macros
*/
#if defined(SQLITE_DEBUG) && 0
  int sqlite3PcacheTrace = 1;
# define pcacheTrace(X) if(sqlite3PcacheTrace){sqlite3DebugPrintf X;}
























#else
# define pcacheTrace(X)

#endif

/********************************** Linked List Management ********************/

/* Allowed values for second argument to pcacheManageDirtyList() */
#define PCACHE_DIRTYLIST_REMOVE   1    /* Remove pPage from dirty list */
#define PCACHE_DIRTYLIST_ADD      2    /* Add pPage to the dirty list */
................................................................................
    ** entries of the dirty-list for a page with NEED_SYNC clear anyway.  */
    if( !p->pSynced 
     && 0==(pPage->flags&PGHDR_NEED_SYNC)   /*OPTIMIZATION-IF-FALSE*/
    ){
      p->pSynced = pPage;
    }
  }

}

/*
** Wrapper around the pluggable caches xUnpin method. If the cache is
** being used for an in-memory database, this function is a no-op.
*/
static void pcacheUnpin(PgHdr *p){
  if( p->pCache->bPurgeable ){
    pcacheTrace(("%p.UNPIN %d\n", p->pCache, p->pgno));
    sqlite3GlobalConfig.pcache2.xUnpin(p->pCache->pCache, p->pPage, 0);

  }
}

/*
** Compute the number of pages of cache requested.   p->szCache is the
** cache size requested by the "PRAGMA cache_size" statement.
*/
................................................................................
                  "spill page %d making room for %d - cache used: %d/%d",
                  pPg->pgno, pgno,
                  sqlite3GlobalConfig.pcache.xPagecount(pCache->pCache),
                numberOfCachePages(pCache));
#endif
      pcacheTrace(("%p.SPILL %d\n",pCache,pPg->pgno));
      rc = pCache->xStress(pCache->pStress, pPg);

      if( rc!=SQLITE_OK && rc!=SQLITE_BUSY ){
        return rc;
      }
    }
  }
  *ppPage = sqlite3GlobalConfig.pcache2.xFetch(pCache->pCache, pgno, 2);
  return *ppPage==0 ? SQLITE_NOMEM_BKPT : SQLITE_OK;
................................................................................
}

/*
** Make every page in the cache clean.
*/
void sqlite3PcacheCleanAll(PCache *pCache){
  PgHdr *p;

  while( (p = pCache->pDirty)!=0 ){
    sqlite3PcacheMakeClean(p);
  }
}

/*
** Clear the PGHDR_NEED_SYNC and PGHDR_WRITEABLE flag from all dirty pages.
*/
void sqlite3PcacheClearWritable(PCache *pCache){
  PgHdr *p;

  for(p=pCache->pDirty; p; p=p->pDirtyNext){
    p->flags &= ~(PGHDR_NEED_SYNC|PGHDR_WRITEABLE);
  }
  pCache->pSynced = pCache->pDirtyTail;
}

/*

  sqlite3_pcache *pCache;             /* Pluggable cache module */
};

/*
** Debug tracing macros
*/
#if defined(SQLITE_DEBUG) && 0
  int sqlite3PcacheTrace = 2;
# define pcacheTrace(X) if(sqlite3PcacheTrace){sqlite3DebugPrintf X;}
  void pcacheDump(PCache *pCache){
    int N;
    int i, j;
    sqlite3_pcache_page *pLower;
    PgHdr *pPg;
    unsigned char *a;
  
    if( sqlite3PcacheTrace<2 ) return;
    if( pCache->pCache==0 ) return;
    N = sqlite3PcachePagecount(pCache);
    if( N>5 ) N = 5;
    for(i=1; i<=N; i++){
       pLower = sqlite3GlobalConfig.pcache2.xFetch(pCache->pCache, i, 0);
       if( pLower==0 ) continue;
       pPg = (PgHdr*)pLower->pExtra;
       printf("%3d: nRef %2d flgs %02x data ", i, pPg->nRef, pPg->flags);
       a = (unsigned char *)pLower->pBuf;
       for(j=0; j<12; j++) printf("%02x", a[j]);
       printf("\n");
       if( pPg->pPage==0 ){
         sqlite3GlobalConfig.pcache2.xUnpin(pCache->pCache, pLower, 0);
       }
    }
  }
  #else
# define pcacheTrace(X)
# define pcacheDump(X)
#endif

/********************************** Linked List Management ********************/

/* Allowed values for second argument to pcacheManageDirtyList() */
#define PCACHE_DIRTYLIST_REMOVE   1    /* Remove pPage from dirty list */
#define PCACHE_DIRTYLIST_ADD      2    /* Add pPage to the dirty list */
................................................................................
    ** entries of the dirty-list for a page with NEED_SYNC clear anyway.  */
    if( !p->pSynced 
     && 0==(pPage->flags&PGHDR_NEED_SYNC)   /*OPTIMIZATION-IF-FALSE*/
    ){
      p->pSynced = pPage;
    }
  }
  pcacheDump(p);
}

/*
** Wrapper around the pluggable caches xUnpin method. If the cache is
** being used for an in-memory database, this function is a no-op.
*/
static void pcacheUnpin(PgHdr *p){
  if( p->pCache->bPurgeable ){
    pcacheTrace(("%p.UNPIN %d\n", p->pCache, p->pgno));
    sqlite3GlobalConfig.pcache2.xUnpin(p->pCache->pCache, p->pPage, 0);
    pcacheDump(p->pCache);
  }
}

/*
** Compute the number of pages of cache requested.   p->szCache is the
** cache size requested by the "PRAGMA cache_size" statement.
*/
................................................................................
                  "spill page %d making room for %d - cache used: %d/%d",
                  pPg->pgno, pgno,
                  sqlite3GlobalConfig.pcache.xPagecount(pCache->pCache),
                numberOfCachePages(pCache));
#endif
      pcacheTrace(("%p.SPILL %d\n",pCache,pPg->pgno));
      rc = pCache->xStress(pCache->pStress, pPg);
      pcacheDump(pCache);
      if( rc!=SQLITE_OK && rc!=SQLITE_BUSY ){
        return rc;
      }
    }
  }
  *ppPage = sqlite3GlobalConfig.pcache2.xFetch(pCache->pCache, pgno, 2);
  return *ppPage==0 ? SQLITE_NOMEM_BKPT : SQLITE_OK;
................................................................................
}

/*
** Make every page in the cache clean.
*/
void sqlite3PcacheCleanAll(PCache *pCache){
  PgHdr *p;
  pcacheTrace(("%p.CLEAN-ALL\n",pCache));
  while( (p = pCache->pDirty)!=0 ){
    sqlite3PcacheMakeClean(p);
  }
}

/*
** Clear the PGHDR_NEED_SYNC and PGHDR_WRITEABLE flag from all dirty pages.
*/
void sqlite3PcacheClearWritable(PCache *pCache){
  PgHdr *p;
  pcacheTrace(("%p.CLEAR-WRITEABLE\n",pCache));
  for(p=pCache->pDirty; p; p=p->pDirtyNext){
    p->flags &= ~(PGHDR_NEED_SYNC|PGHDR_WRITEABLE);
  }
  pCache->pSynced = pCache->pDirtyTail;
}

/*