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Comment:Change the pager's sector size algorithm to the maximum of the size reported by xSectorSize() from the VFS and 512. It was using the maximum of xSectorSize() and the current page size, but that was adding an extra 512 bytes to the size of the journal file in the common case. (CVS 4929)
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SHA1: 17ea0c97a8bac1b34af1f9183d93a2f2a6af9690
User & Date: drh 2008-03-28 17:41:14
Context
2008-03-28
18:11
Fix for #3022. Handle queries like "SELECT min(b) FROM T WHERE a = X AND b > X" when there is an index on (a,b). (CVS 4930) check-in: bce28975 user: danielk1977 tags: trunk
17:41
Change the pager's sector size algorithm to the maximum of the size reported by xSectorSize() from the VFS and 512. It was using the maximum of xSectorSize() and the current page size, but that was adding an extra 512 bytes to the size of the journal file in the common case. (CVS 4929) check-in: 17ea0c97 user: drh tags: trunk
15:44
Changes to the Mem structure to reduce the frequency of freeing and reallocating the dynamic buffer. (CVS 4928) check-in: d0bf73d8 user: danielk1977 tags: trunk
Changes
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Changes to src/pager.c.

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** 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 1.421 2008/03/27 22:42:52 drh Exp $
*/
#ifndef SQLITE_OMIT_DISKIO
#include "sqliteInt.h"
#include <assert.h>
#include <string.h>

/*
................................................................................
  }
  return rc;
}

/*
** Set the sectorSize for the given pager.
**
** The sector size is the larger of the sector size reported
** by sqlite3OsSectorSize() and the pageSize.
*/
static void setSectorSize(Pager *pPager){
  assert(pPager->fd->pMethods||pPager->tempFile);
  if( !pPager->tempFile ){
    /* Sector size doesn't matter for temporary files. Also, the file
    ** may not have been opened yet, in whcih case the OsSectorSize()
    ** call will segfault.
    */
    pPager->sectorSize = sqlite3OsSectorSize(pPager->fd);
  }
  if( pPager->sectorSize<pPager->pageSize ){
    pPager->sectorSize = pPager->pageSize;
  }
}

/*
** Playback the journal and thus restore the database file to
** the state it was in before we started making changes.  
**
................................................................................
**  (2)  4 byte big-endian integer which is the number of valid page records
**       in the journal.  If this value is 0xffffffff, then compute the
**       number of page records from the journal size.
**  (3)  4 byte big-endian integer which is the initial value for the 
**       sanity checksum.
**  (4)  4 byte integer which is the number of pages to truncate the
**       database to during a rollback.



**  (5)  4 byte integer which is the number of bytes in the master journal
**       name.  The value may be zero (indicate that there is no master
**       journal.)
**  (6)  N bytes of the master journal name.  The name will be nul-terminated
**       and might be shorter than the value read from (5).  If the first byte
**       of the name is \000 then there is no master journal.  The master
**       journal name is stored in UTF-8.
**  (7)  Zero or more pages instances, each as follows:
**        +  4 byte page number.
**        +  pPager->pageSize bytes of data.
**        +  4 byte checksum
**
** When we speak of the journal header, we mean the first 6 items above.
** Each entry in the journal is an instance of the 7th item.
**
** Call the value from the second bullet "nRec".  nRec is the number of
** valid page entries in the journal.  In most cases, you can compute the
** value of nRec from the size of the journal file.  But if a power
** failure occurred while the journal was being written, it could be the
** case that the size of the journal file had already been increased but
** the extra entries had not yet made it safely to disk.  In such a case,







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** 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 1.422 2008/03/28 17:41:14 drh Exp $
*/
#ifndef SQLITE_OMIT_DISKIO
#include "sqliteInt.h"
#include <assert.h>
#include <string.h>

/*
................................................................................
  }
  return rc;
}

/*
** Set the sectorSize for the given pager.
**
** The sector size is at least as big as the sector size reported
** by sqlite3OsSectorSize().  The minimum sector size is 512.
*/
static void setSectorSize(Pager *pPager){
  assert(pPager->fd->pMethods||pPager->tempFile);
  if( !pPager->tempFile ){
    /* Sector size doesn't matter for temporary files. Also, the file
    ** may not have been opened yet, in whcih case the OsSectorSize()
    ** call will segfault.
    */
    pPager->sectorSize = sqlite3OsSectorSize(pPager->fd);
  }
  if( pPager->sectorSize<512 ){
    pPager->sectorSize = 512;
  }
}

/*
** Playback the journal and thus restore the database file to
** the state it was in before we started making changes.  
**
................................................................................
**  (2)  4 byte big-endian integer which is the number of valid page records
**       in the journal.  If this value is 0xffffffff, then compute the
**       number of page records from the journal size.
**  (3)  4 byte big-endian integer which is the initial value for the 
**       sanity checksum.
**  (4)  4 byte integer which is the number of pages to truncate the
**       database to during a rollback.
**  (5)  4 byte big-endian integer which is the sector size.  The header
**       is this many bytes in size.
**  (6)  4 byte big-endian integer which is the page case.
**  (7)  4 byte integer which is the number of bytes in the master journal
**       name.  The value may be zero (indicate that there is no master
**       journal.)
**  (8)  N bytes of the master journal name.  The name will be nul-terminated
**       and might be shorter than the value read from (5).  If the first byte
**       of the name is \000 then there is no master journal.  The master
**       journal name is stored in UTF-8.
**  (9)  Zero or more pages instances, each as follows:
**        +  4 byte page number.
**        +  pPager->pageSize bytes of data.
**        +  4 byte checksum
**
** When we speak of the journal header, we mean the first 8 items above.
** Each entry in the journal is an instance of the 9th item.
**
** Call the value from the second bullet "nRec".  nRec is the number of
** valid page entries in the journal.  In most cases, you can compute the
** value of nRec from the size of the journal file.  But if a power
** failure occurred while the journal was being written, it could be the
** case that the size of the journal file had already been increased but
** the extra entries had not yet made it safely to disk.  In such a case,

Changes to test/io.test.

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#
#***********************************************************************
#
# The focus of this file is testing some specific characteristics of the 
# IO traffic generated by SQLite (making sure SQLite is not writing out
# more database pages than it has to, stuff like that).
#
# $Id: io.test,v 1.14 2008/01/22 11:50:13 danielk1977 Exp $

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

db close
sqlite3_simulate_device
sqlite3 db test.db -vfs devsym
................................................................................
  #
  #    <jrnl file size> = <jrnl header size> + nPage * (<page-size> + 8)
  #
  # If the journal file contains additional headers, this formula
  # will not predict the size of the journal file.
  #
  file size test.db-journal
} [expr 1024 + (1024+8)*41]

#----------------------------------------------------------------------
# Test cases io-5.* test that the default page size is selected and
# used correctly.
#
set tn 0
foreach {char                 sectorsize pgsize} {







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#
#***********************************************************************
#
# The focus of this file is testing some specific characteristics of the 
# IO traffic generated by SQLite (making sure SQLite is not writing out
# more database pages than it has to, stuff like that).
#
# $Id: io.test,v 1.15 2008/03/28 17:41:14 drh Exp $

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

db close
sqlite3_simulate_device
sqlite3 db test.db -vfs devsym
................................................................................
  #
  #    <jrnl file size> = <jrnl header size> + nPage * (<page-size> + 8)
  #
  # If the journal file contains additional headers, this formula
  # will not predict the size of the journal file.
  #
  file size test.db-journal
} [expr 512 + (1024+8)*41]

#----------------------------------------------------------------------
# Test cases io-5.* test that the default page size is selected and
# used correctly.
#
set tn 0
foreach {char                 sectorsize pgsize} {