SQLite

  int pageSize;               /* Number of bytes in a page */
  Pgno mxPgno;                /* Maximum allowed size of the database */
  i64 journalSizeLimit;       /* Size limit for persistent journal files */
  char *zFilename;            /* Name of the database file */
  char *zJournal;             /* Name of the journal file */
  int (*xBusyHandler)(void*); /* Function to call when busy */
  void *pBusyHandlerArg;      /* Context argument for xBusyHandler */
  int nHit, nMiss;            /* Total cache hits and misses */
#ifdef SQLITE_TEST

  int nRead, nWrite;          /* Database pages read/written */
#endif
  void (*xReiniter)(DbPage*); /* Call this routine when reloading pages */
#ifdef SQLITE_HAS_CODEC
  void *(*xCodec)(void*,void*,Pgno,int); /* Routine for en/decoding data */
  void (*xCodecSizeChng)(void*,int,int); /* Notify of page size changes */
  void (*xCodecFree)(void*);             /* Destructor for the codec */

  ** pages belonging to the same sector.
  **
  ** The doNotSpill flag inhibits all cache spilling regardless of whether
  ** or not a sync is required.  This is set during a rollback.
  **
  ** Spilling is also prohibited when in an error state since that could
  ** lead to database corruption.   In the current implementaton it 
  ** is impossible for sqlite3PcacheFetch() to be called with createFlag==1
  ** while in the error state, hence it is impossible for this routine to
  ** be called in the error state.  Nevertheless, we include a NEVER()
  ** test for the error state as a safeguard against future changes.
  */
  if( NEVER(pPager->errCode) ) return SQLITE_OK;
  if( pPager->doNotSpill ) return SQLITE_OK;
  if( pPager->doNotSyncSpill && (pPg->flags & PGHDR_NEED_SYNC)!=0 ){

  assert( (*ppPage)->pgno==pgno );
  assert( (*ppPage)->pPager==pPager || (*ppPage)->pPager==0 );

  if( (*ppPage)->pPager && !noContent ){
    /* In this case the pcache already contains an initialized copy of
    ** the page. Return without further ado.  */
    assert( pgno<=PAGER_MAX_PGNO && pgno!=PAGER_MJ_PGNO(pPager) );
    pPager->nHit++;
    return SQLITE_OK;

  }else{
    /* The pager cache has created a new page. Its content needs to 
    ** be initialized.  */


    pPg = *ppPage;
    pPg->pPager = pPager;

    /* The maximum page number is 2^31. Return SQLITE_CORRUPT if a page
    ** number greater than this, or the unused locking-page, is requested. */
    if( pgno>PAGER_MAX_PGNO || pgno==PAGER_MJ_PGNO(pPager) ){
      rc = SQLITE_CORRUPT_BKPT;

        testcase( rc==SQLITE_NOMEM );
        sqlite3EndBenignMalloc();
      }
      memset(pPg->pData, 0, pPager->pageSize);
      IOTRACE(("ZERO %p %d\n", pPager, pgno));
    }else{
      assert( pPg->pPager==pPager );
      pPager->nMiss++;
      rc = readDbPage(pPg);
      if( rc!=SQLITE_OK ){
        goto pager_acquire_err;
      }
    }
    pager_set_pagehash(pPg);
  }

  a[7] = pPager->nMiss;
  a[8] = 0;  /* Used to be pPager->nOvfl */
  a[9] = pPager->nRead;
  a[10] = pPager->nWrite;
  return a;
}
#endif

/*
** Parameter eStat must be either SQLITE_DBSTATUS_CACHE_HIT or
** SQLITE_DBSTATUS_CACHE_MISS. Before returning, *pnVal is incremented by the
** current cache hit or miss count, according to the value of eStat. If the 
** reset parameter is non-zero, the cache hit or miss count is zeroed before 
** returning.
*/
void sqlite3PagerCacheStat(Pager *pPager, int eStat, int reset, int *pnVal){
  int *piStat;

  assert( eStat==SQLITE_DBSTATUS_CACHE_HIT
       || eStat==SQLITE_DBSTATUS_CACHE_MISS
  );
  if( eStat==SQLITE_DBSTATUS_CACHE_HIT ){
    piStat = &pPager->nHit;
  }else{
    piStat = &pPager->nMiss;
  }

  *pnVal += *piStat;
  if( reset ){
    *piStat = 0;
  }
}

/*
** Return true if this is an in-memory pager.
*/
int sqlite3PagerIsMemdb(Pager *pPager){
  return MEMDB;
}

const char *sqlite3PagerFilename(Pager*);
const sqlite3_vfs *sqlite3PagerVfs(Pager*);
sqlite3_file *sqlite3PagerFile(Pager*);
const char *sqlite3PagerJournalname(Pager*);
int sqlite3PagerNosync(Pager*);
void *sqlite3PagerTempSpace(Pager*);
int sqlite3PagerIsMemdb(Pager*);
void sqlite3PagerCacheStat(Pager *, int, int, int *);

/* Functions used to truncate the database file. */
void sqlite3PagerTruncateImage(Pager*,Pgno);

#if defined(SQLITE_HAS_CODEC) && !defined(SQLITE_OMIT_WAL)
void *sqlite3PagerCodec(DbPage *);
#endif

**
** [[SQLITE_DBSTATUS_STMT_USED]] ^(<dt>SQLITE_DBSTATUS_STMT_USED</dt>
** <dd>This parameter returns the approximate number of of bytes of heap
** and lookaside memory used by all prepared statements associated with
** the database connection.)^
** ^The highwater mark associated with SQLITE_DBSTATUS_STMT_USED is always 0.
** </dd>
**
** [[SQLITE_DBSTATUS_CACHE_HIT]] ^(<dt>SQLITE_DBSTATUS_CACHE_HIT</dt>
** <dd>This parameter returns the number of pager cache hits that have
** occurred. ^The highwater mark associated with SQLITE_DBSTATUS_CACHE_HIT 
** is always 0.
** </dd>
**
** [[SQLITE_DBSTATUS_CACHE_MISS]] ^(<dt>SQLITE_DBSTATUS_CACHE_MISS</dt>
** <dd>This parameter returns the number of pager cache misses that have
** occurred. ^The highwater mark associated with SQLITE_DBSTATUS_CACHE_MISS 
** is always 0.
** </dd>
** </dl>
*/
#define SQLITE_DBSTATUS_LOOKASIDE_USED       0
#define SQLITE_DBSTATUS_CACHE_USED           1
#define SQLITE_DBSTATUS_SCHEMA_USED          2
#define SQLITE_DBSTATUS_STMT_USED            3
#define SQLITE_DBSTATUS_LOOKASIDE_HIT        4
#define SQLITE_DBSTATUS_LOOKASIDE_MISS_SIZE  5
#define SQLITE_DBSTATUS_LOOKASIDE_MISS_FULL  6
#define SQLITE_DBSTATUS_CACHE_HIT            7
#define SQLITE_DBSTATUS_CACHE_MISS           8
#define SQLITE_DBSTATUS_MAX                  8   /* Largest defined DBSTATUS */


/*
** CAPI3REF: Prepared Statement Status
**
** ^(Each prepared statement maintains various
** [SQLITE_STMTSTATUS counters] that measure the number

**
** [[SQLITE_STMTSTATUS_AUTOINDEX]] <dt>SQLITE_STMTSTATUS_AUTOINDEX</dt>
** <dd>^This is the number of rows inserted into transient indices that
** were created automatically in order to help joins run faster.
** A non-zero value in this counter may indicate an opportunity to
** improvement performance by adding permanent indices that do not
** need to be reinitialized each time the statement is run.</dd>

** </dl>
*/
#define SQLITE_STMTSTATUS_FULLSCAN_STEP     1
#define SQLITE_STMTSTATUS_SORT              2
#define SQLITE_STMTSTATUS_AUTOINDEX         3

/*

      db->pnBytesFreed = 0;

      *pHighwater = 0;
      *pCurrent = nByte;

      break;
    }

    /*
    ** Set *pCurrent to the total cache hits or misses encountered by all
    ** pagers the database handle is connected to. *pHighwater is always set 
    ** to zero.
    */
    case SQLITE_DBSTATUS_CACHE_HIT:
    case SQLITE_DBSTATUS_CACHE_MISS: {
      int i;
      int nRet = 0;
      assert( SQLITE_DBSTATUS_CACHE_MISS==SQLITE_DBSTATUS_CACHE_HIT+1 );

      for(i=0; i<db->nDb; i++){
        if( db->aDb[i].pBt ){
          Pager *pPager = sqlite3BtreePager(db->aDb[i].pBt);
          sqlite3PagerCacheStat(pPager, op, resetFlag, &nRet);
        }
      }
      *pHighwater = 0;
      *pCurrent = nRet;
      break;
    }

    default: {
      rc = SQLITE_ERROR;
    }
  }
  sqlite3_mutex_leave(db->mutex);
  return rc;

  } aOp[] = {
    { "LOOKASIDE_USED",      SQLITE_DBSTATUS_LOOKASIDE_USED      },
    { "CACHE_USED",          SQLITE_DBSTATUS_CACHE_USED          },
    { "SCHEMA_USED",         SQLITE_DBSTATUS_SCHEMA_USED         },
    { "STMT_USED",           SQLITE_DBSTATUS_STMT_USED           },
    { "LOOKASIDE_HIT",       SQLITE_DBSTATUS_LOOKASIDE_HIT       },
    { "LOOKASIDE_MISS_SIZE", SQLITE_DBSTATUS_LOOKASIDE_MISS_SIZE },
    { "LOOKASIDE_MISS_FULL", SQLITE_DBSTATUS_LOOKASIDE_MISS_FULL },
    { "CACHE_HIT",           SQLITE_DBSTATUS_CACHE_HIT           },
    { "CACHE_MISS",          SQLITE_DBSTATUS_CACHE_MISS          }
  };
  Tcl_Obj *pResult;
  if( objc!=4 ){
    Tcl_WrongNumArgs(interp, 1, objv, "DB PARAMETER RESETFLAG");
    return TCL_ERROR;
  }
  if( getDbPointer(interp, Tcl_GetString(objv[1]), &db) ) return TCL_ERROR;
  zOpName = Tcl_GetString(objv[2]);
  if( memcmp(zOpName, "SQLITE_", 7)==0 ) zOpName += 7;
  if( memcmp(zOpName, "DBSTATUS_", 9)==0 ) zOpName += 9;
  for(i=0; i<ArraySize(aOp); i++){

# 2011 September 20
#
# 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.
#
#***********************************************************************
#
# Tests for the sqlite3_stmt_status() function
#

set testdir [file dirname $argv0]
source $testdir/tester.tcl

set ::testprefix dbstatus2

do_execsql_test 1.0 {
  PRAGMA page_size = 1024;
  PRAGMA auto_vacuum = 0;

  CREATE TABLE t1(a PRIMARY KEY, b);
  INSERT INTO t1 VALUES(1, randomblob(600));
  INSERT INTO t1 VALUES(2, randomblob(600));
  INSERT INTO t1 VALUES(3, randomblob(600));
}

proc db_hit_miss {db {reset 0}} {
  set nHit  [sqlite3_db_status $db CACHE_HIT $reset]
  set nMiss [sqlite3_db_status $db CACHE_MISS $reset]
  list $nHit $nMiss
}

do_test 1.1 {
  db close
  sqlite3 db test.db
  expr {[file size test.db] / 1024}
} 6

do_test 1.2 {
  execsql { SELECT b FROM t1 WHERE a=2 }
  db_hit_miss db
} {{0 2 0} {0 4 0}}

do_test 1.3 { 
  execsql { SELECT b FROM t1 WHERE a=2 }
  db_hit_miss db
} {{0 6 0} {0 4 0}}

do_test 1.4 { 
  execsql { SELECT b FROM t1 WHERE a=2 }
  db_hit_miss db
} {{0 10 0} {0 4 0}}

do_test 1.5 { 
  db_hit_miss db 1
} {{0 10 0} {0 4 0}}

do_test 1.6 { 
  db_hit_miss db 0
} {{0 0 0} {0 0 0}}

do_test 1.7 {
  set fd [db incrblob main t1 b 1]
  fconfigure $fd -translation binary
  set len [string length [read $fd]]
  close $fd
  set len
} 600
do_test 1.8 { sqlite3_db_status db CACHE_HIT  0 } {0 2 0}
do_test 1.9 { sqlite3_db_status db CACHE_MISS 0 } {0 1 0}

 
finish_test