SQLite

** The pager is used to access a database disk file.  It implements
** atomic commit and rollback through the use of a journal file that
** is separate from the database file.  The pager also implements file
** locking to prevent two processes from writing the same database
** file simultaneously, or one process from reading the database while
** another is writing.
**
** @(#) $Id: pager.c,v 1.404 2008/01/22 21:30:53 drh Exp $
*/
#ifndef SQLITE_OMIT_DISKIO
#include "sqliteInt.h"
#include <assert.h>
#include <string.h>

/*

    assert( p->iInUseDB>=0 );
  }
#else
# define pagerEnter(X)
# define pagerLeave(X)
#endif

/*
** Enable reference count tracking (for debugging) here:
*/
#ifdef SQLITE_DEBUG
  int pager3_refinfo_enable = 0;
  static void pager_refinfo(PgHdr *p){
    static int cnt = 0;
    if( !pager3_refinfo_enable ) return;
    sqlite3DebugPrintf(
       "REFCNT: %4d addr=%p nRef=%-3d total=%d\n",
       p->pgno, PGHDR_TO_DATA(p), p->nRef, p->pPager->nRef
    );
    cnt++;   /* Something to set a breakpoint on */
  }
# define REFINFO(X)  pager_refinfo(X)
#else
# define REFINFO(X)
#endif

/*
** Add page pPg to the end of the linked list managed by structure
** pList (pPg becomes the last entry in the list - the most recently 
** used). Argument pLink should point to either pPg->free or pPg->gfree,
** depending on whether pPg is being added to the pager-specific or
** global LRU list.
*/

static void _page_ref(PgHdr *pPg){
  if( pPg->nRef==0 ){
    /* The page is currently on the freelist.  Remove it. */
    lruListRemove(pPg);
    pPg->pPager->nRef++;
  }
  pPg->nRef++;
  REFINFO(pPg);
}
#ifdef SQLITE_DEBUG
  static void page_ref(PgHdr *pPg){
    if( pPg->nRef==0 ){
      _page_ref(pPg);
    }else{
      pPg->nRef++;
      REFINFO(pPg);
    }
  }
#else
# define page_ref(P)   ((P)->nRef==0?_page_ref(P):(void)(P)->nRef++)
#endif

/*

    }else{
      pPg->inJournal = 0;
      pPg->needSync = 0;
    }

    makeClean(pPg);
    pPg->nRef = 1;
    REFINFO(pPg);

    pPager->nRef++;
    if( pPager->nExtra>0 ){
      memset(PGHDR_TO_EXTRA(pPg, pPager), 0, pPager->nExtra);
    }
    nMax = sqlite3PagerPagecount(pPager);
    if( pPager->errCode ){

  Pager *pPager = pPg->pPager;

  /* Decrement the reference count for this page
  */
  assert( pPg->nRef>0 );
  pagerEnter(pPg->pPager);
  pPg->nRef--;
  REFINFO(pPg);

  CHECK_PAGE(pPg);

  /* When the number of references to a page reach 0, call the
  ** destructor and add the page to the freelist.
  */
  if( pPg->nRef==0 ){

**    May you share freely, never taking more than you give.
**
*************************************************************************
** This header file defines the interface that the sqlite page cache
** subsystem.  The page cache subsystem reads and writes a file a page
** at a time and provides a journal for rollback.
**
** @(#) $Id: pager.h,v 1.68 2007/11/28 16:19:56 drh Exp $
*/

#ifndef _PAGER_H_
#define _PAGER_H_

/*
** The type used to represent a page number.  The first page in a file

  Pgno sqlite3PagerPagenumber(DbPage*);
  int sqlite3PagerIswriteable(DbPage*);
#endif

#ifdef SQLITE_TEST
  int *sqlite3PagerStats(Pager*);
  void sqlite3PagerRefdump(Pager*);
  int pager3_refinfo_enable;
#endif

#ifdef SQLITE_TEST
void disable_simulated_io_errors(void);
void enable_simulated_io_errors(void);
#else
# define disable_simulated_io_errors()
# define enable_simulated_io_errors()
#endif

#endif /* _PAGER_H_ */

**    May you share freely, never taking more than you give.
**
*************************************************************************
** Code for testing the btree.c module in SQLite.  This code
** is not included in the SQLite library.  It is used for automated
** testing of the SQLite library.
**
** $Id: test3.c,v 1.89 2008/01/19 23:50:26 drh Exp $
*/
#include "sqliteInt.h"
#include "btreeInt.h"
#include "tcl.h"
#include <stdlib.h>
#include <string.h>

     { "btree_cursor_list",        (Tcl_CmdProc*)btree_cursor_list        },
  };
  int i;

  for(i=0; i<sizeof(aCmd)/sizeof(aCmd[0]); i++){
    Tcl_CreateCommand(interp, aCmd[i].zName, aCmd[i].xProc, 0, 0);
  }
  Tcl_LinkVar(interp, "pager_refinfo_enable", (char*)&pager3_refinfo_enable,
     TCL_LINK_INT);
  Tcl_LinkVar(interp, "btree_trace", (char*)&sqlite3_btree_trace,
     TCL_LINK_INT);

  /* The btree_insert command is implemented using the tcl 'object'
  ** interface, not the string interface like the other commands in this
  ** file. This is so binary data can be inserted into btree tables.
  */
  Tcl_CreateObjCommand(interp, "btree_insert", btree_insert, 0, 0);
  return TCL_OK;
}

# 2001 September 15
#
# 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 file implements regression tests for SQLite library.  The
# focus of this script is btree database backend
#
# $Id: btree.test,v 1.42 2008/01/19 23:50:26 drh Exp $


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

ifcapable default_autovacuum {
  finish_test

do_test btree-9.1 {
  for {set i 1} {$i<=19} {incr i} {
    set key [format %03d $i]
    set data "*** $key *** $key *** $key *** $key ***"
    btree_insert $::c1 $key $data
  }
} {}
#btree_tree_dump $::b1 2
#btree_pager_ref_dump $::b1
#set pager_refinfo_enable 1
do_test btree-9.2 {
  btree_insert $::c1 020 {*** 020 *** 020 *** 020 *** 020 ***}
  select_keys $::c1
} {001 002 003 004 005 006 007 008 009 010 011 012 013 014 015 016 017 018 019 020}
#btree_page_dump $::b1 2
#btree_pager_ref_dump $::b1
#set pager_refinfo_enable 0

# The previous "select_keys" command left the cursor pointing at the root
# page.  So there should only be two pages checked out.  2 (the root) and
# page 1.
do_test btree-9.2.1 {
  lindex [btree_pager_stats $::b1] 1
} {2}