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 1.329 2007/04/16 15:02:19 drh Exp $
*/
#ifndef SQLITE_OMIT_DISKIO
#include "sqliteInt.h"
#include "os.h"
#include "pager.h"
#include <assert.h>
#include <string.h>

#endif
  int nHash;                  /* Size of the pager hash table */
  PgHdr **aHash;              /* Hash table to map page number to PgHdr */
#ifdef SQLITE_ENABLE_MEMORY_MANAGEMENT
  Pager *pNext;               /* Linked list of pagers in this thread */
#endif
  char *pTmpSpace;            /* Pager.pageSize bytes of space for tmp use */
  char dbFileVers[16];        /* Changes whenever database file changes */
};

/*
** The following global variables hold counters used for
** testing purposes only.  These variables do not exist in
** a non-testing build.  These variables are not thread-safe.
*/

    memcpy(pData, aData, pPager->pageSize);
    if( pPager->xReiniter ){
      pPager->xReiniter(pPg, pPager->pageSize);
    }
#ifdef SQLITE_CHECK_PAGES
    pPg->pageHash = pager_pagehash(pPg);
#endif


    /* If this was page 1, then restore the value of Pager.dbFileVers.
    ** Do this before any decoding. */
    if( pgno==1 ){
      memcpy(&pPager->dbFileVers, &((u8*)pData)[24],sizeof(pPager->dbFileVers));
    }

    /* Decode the page just read from disk */
    CODEC1(pPager, pData, pPg->pgno, 3);
  }
  return rc;
}

/*
** Parameter zMaster is the name of a master journal file. A single journal
** file that referred to the master journal file has just been rolled back.

    if( pList->pgno<=pPager->dbSize ){
      char *pData = CODEC2(pPager, PGHDR_TO_DATA(pList), pList->pgno, 6);
      PAGERTRACE3("STORE %d page %d\n", PAGERID(pPager), pList->pgno);
      IOTRACE(("PGOUT %p %d\n", pPager, pList->pgno));
      rc = sqlite3OsWrite(pPager->fd, pData, pPager->pageSize);
      PAGER_INCR(sqlite3_pager_writedb_count);
      PAGER_INCR(pPager->nWrite);
      if( pList->pgno==1 ){
        memcpy(&pPager->dbFileVers, &pData[24], sizeof(pPager->dbFileVers));
      }
    }
#ifndef NDEBUG
    else{
      PAGERTRACE3("NOSTORE %d page %d\n", PAGERID(pPager), pList->pgno);
    }
#endif
    if( rc ) return rc;

    rc = sqlite3OsRead(pPager->fd, PGHDR_TO_DATA(pPg),
                          pPager->pageSize);
  }
  PAGER_INCR(sqlite3_pager_readdb_count);
  PAGER_INCR(pPager->nRead);
  IOTRACE(("PGIN %p %d\n", pPager, pgno));
  PAGERTRACE3("FETCH %d page %d\n", PAGERID(pPager), pPg->pgno);
  if( pgno==1 ){
    memcpy(&pPager->dbFileVers, &((u8*)PGHDR_TO_DATA(pPg))[24],
                                              sizeof(pPager->dbFileVers));
  }
  CODEC1(pPager, PGHDR_TO_DATA(pPg), pPg->pgno, 3);
  return rc;
}


/*
** This function is called to obtain the shared lock required before

            (pPager->exclusiveMode && pPager->state>PAGER_SHARED)
        );
      }

      if( pPager->pAll ){
        /* The shared-lock has just been acquired on the database file
        ** and there are already pages in the cache (from a previous
        ** read or write transaction).  Check to see if the database

        ** has been modified.  If the database has changed, flush the
        ** cache.
        **
        ** Database changes is detected by looking at 15 bytes beginning
        ** at offset 24 into the file.  The first 4 of these 16 bytes are
        ** a 32-bit counter that is incremented with each change.  The
        ** other bytes change randomly with each file change when
        ** a codec is in use.
        ** 
        ** There is a vanishingly small chance that a change will not be 
        ** deteched.  The chance of an undetected change is so small that
        ** it can be neglected.
        */


        char dbFileVers[sizeof(pPager->dbFileVers)];
        sqlite3PagerPagecount(pPager);

        if( pPager->errCode ){
          return pPager->errCode;
        }

        if( pPager->dbSize>0 ){

          rc = sqlite3OsSeek(pPager->fd, 24);
          if( rc!=SQLITE_OK ){
            return rc;
          }
          rc = sqlite3OsRead(pPager->fd, &dbFileVers, sizeof(dbFileVers));
          if( rc!=SQLITE_OK ){
            return rc;
          }
        }else{
          memset(dbFileVers, 0, sizeof(dbFileVers));
        }

        if( memcmp(pPager->dbFileVers, dbFileVers, sizeof(dbFileVers))!=0 ){
          pager_reset(pPager);

        }
      }
    }
    assert( pPager->exclusiveMode || pPager->state<=PAGER_SHARED );
    if( pPager->state==PAGER_UNLOCK ){
      pPager->state = PAGER_SHARED;
    }

      rc = readDbPage(pPager, pPg, pgno);
      if( rc!=SQLITE_OK && rc!=SQLITE_IOERR_SHORT_READ ){
        pPg->pgno = 0;
        sqlite3PagerUnref(pPg);
        return rc;
      }
    }





    /* Link the page into the page hash table */
    h = pgno & (pPager->nHash-1);
    assert( pgno!=0 );
    pPg->pNextHash = pPager->aHash[h];
    pPager->aHash[h] = pPg;
    if( pPg->pNextHash ){

  
    /* Read the current value at byte 24. */
    change_counter = retrieve32bits(pPgHdr, 24);
  
    /* Increment the value just read and write it back to byte 24. */
    change_counter++;
    put32bits(((char*)PGHDR_TO_DATA(pPgHdr))+24, change_counter);

  
    /* Release the page reference. */
    sqlite3PagerUnref(pPgHdr);
    pPager->changeCountDone = 1;
  }
  return SQLITE_OK;
}

# 2007 March 24
#
# 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.
#
# $Id: exclusive2.test,v 1.4 2007/04/16 15:02:20 drh Exp $

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

ifcapable {!pager_pragmas} {
  finish_test
  return

  pagerChangeCounter test.db
} {0}

#-----------------------------------------------------------------------
# The following tests - exclusive2-1.X - check that:
#
# 1-3:   Build a database with connection 1, calculate a signature.
# 4-9:   Modify the database using a second connection in a way that
#        does not modify the freelist, then reset the pager change-counter
#        to the value it had before the modifications.
# 8:     Check that using the first connection, the database signature
#        is still the same. This is because it uses the in-memory cache.
#        It can't tell the db has changed because we reset the change-counter.
# 9:     Increment the change-counter.
# 10:    Ensure that the first connection now sees the updated database. It
#        sees the change-counter has been incremented and discards the 
#        invalid in-memory cache.
#
do_test exclusive2-1.1 {
  execsql {
    BEGIN;
    CREATE TABLE t1(a, b);
    INSERT INTO t1(a) VALUES(randstr(10, 400));
    INSERT INTO t1(a) VALUES(randstr(10, 400));
    INSERT INTO t1(a) SELECT randstr(10, 400) FROM t1;
    INSERT INTO t1(a) SELECT randstr(10, 400) FROM t1;
    INSERT INTO t1(a) SELECT randstr(10, 400) FROM t1;
    INSERT INTO t1(a) SELECT randstr(10, 400) FROM t1;
    INSERT INTO t1(a) SELECT randstr(10, 400) FROM t1;
    COMMIT;
    SELECT count(*) FROM t1;
  }
} {64}
do_test exclusive2-1.2 {
  set ::sig [t1sig]
  pagerChangeCounter test.db
} {1}
do_test exclusive2-1.3 {
  t1sig
} $::sig
do_test exclusive2-1.4 {
  sqlite3 db2 test.db
  t1sig db2
} $::sig
do_test exclusive2-1.5 {
  execsql {
    UPDATE t1 SET b=a, a=NULL;
  } db2
  expr {[t1sig db2] eq $::sig}
} 0
do_test exclusive2-1.6 {
  pagerChangeCounter test.db
} {2}
do_test exclusive2-1.7 {

#        SQLite detects the modified change-counter and discards the
#        in-memory cache. Then it finds the corruption caused in step 4....
#
do_test exclusive2-2.1 {
  execsql {PRAGMA locking_mode = exclusive;}
  execsql {
    BEGIN;
    DELETE FROM t1;
    INSERT INTO t1(a) VALUES(randstr(10, 400));
    INSERT INTO t1(a) VALUES(randstr(10, 400));
    INSERT INTO t1(a) SELECT randstr(10, 400) FROM t1;
    INSERT INTO t1(a) SELECT randstr(10, 400) FROM t1;
    INSERT INTO t1(a) SELECT randstr(10, 400) FROM t1;
    INSERT INTO t1(a) SELECT randstr(10, 400) FROM t1;
    INSERT INTO t1(a) SELECT randstr(10, 400) FROM t1;
    COMMIT;
    SELECT count(*) FROM t1;
  }
} {64}
do_test exclusive2-2.2 {
  set ::sig [t1sig]
  pagerChangeCounter test.db

# 2006 November 23
#
# 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 measuring executing speed.
#
# $Id: speed2.test,v 1.7 2007/04/16 15:02:20 drh Exp $
#

set testdir [file dirname $argv0]
source $testdir/tester.tcl
speed_trial_init speed2

# Set a uniform random seed

# Create a database schema.
#
do_test speed2-1.0 {
  execsql {
    PRAGMA page_size=1024;
    PRAGMA cache_size=8192;
    PRAGMA locking_mode=EXCLUSIVE;
    CREATE TABLE t1(a INTEGER, b INTEGER, c TEXT);
    CREATE TABLE t2(a INTEGER, b INTEGER, c TEXT);
    CREATE INDEX i2a ON t2(a);
    CREATE INDEX i2b ON t2(b);
  }
  execsql {
    SELECT name FROM sqlite_master ORDER BY 1;