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Overview
Comment:Patch the sqlite3PagerWrite() method in the Pager to run a bit faster.
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SHA1:c63311e2f3344363a5ed99838fb5850004eaee30
User & Date: drh 2014-08-24 01:32:43
Context
2014-08-24
02:53
The sqlite3VdbeChangeEncoding() routine goes about 3x faster if the sqlite3VdbeMemTranslate() subroutine is not inlined. check-in: 0c7e1b87 user: drh tags: trunk
01:32
Patch the sqlite3PagerWrite() method in the Pager to run a bit faster. check-in: c63311e2 user: drh tags: trunk
2014-08-23
23:15
Faster implementation of pcache1Fetch() check-in: 0371cc3b user: drh tags: trunk
Changes
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Changes to src/pager.c.

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  /* Update the database size and return.
  */
  if( pPager->dbSize<pPg->pgno ){
    pPager->dbSize = pPg->pgno;
  }
  return rc;
}




























































































/*
** Mark a data page as writeable. This routine must be called before 
** making changes to a page. The caller must check the return value 
** of this function and be careful not to change any page data unless 
** this routine returns SQLITE_OK.
**
................................................................................
** function also deals with the special case where 2 or more pages
** fit on a single disk sector. In this case all co-resident pages
** must have been written to the journal file before returning.
**
** If an error occurs, SQLITE_NOMEM or an IO error code is returned
** as appropriate. Otherwise, SQLITE_OK.
*/
int sqlite3PagerWrite(DbPage *pDbPage){
  int rc = SQLITE_OK;

  PgHdr *pPg = pDbPage;
  Pager *pPager = pPg->pPager;

  assert( (pPg->flags & PGHDR_MMAP)==0 );
  assert( pPager->eState>=PAGER_WRITER_LOCKED );
  assert( pPager->eState!=PAGER_ERROR );
  assert( assert_pager_state(pPager) );

  if( pPager->sectorSize > (u32)pPager->pageSize ){
    Pgno nPageCount;          /* Total number of pages in database file */
    Pgno pg1;                 /* First page of the sector pPg is located on. */
    int nPage = 0;            /* Number of pages starting at pg1 to journal */
    int ii;                   /* Loop counter */
    int needSync = 0;         /* True if any page has PGHDR_NEED_SYNC */
    Pgno nPagePerSector = (pPager->sectorSize/pPager->pageSize);

    /* Set the doNotSpill NOSYNC bit to 1. This is because we cannot allow
    ** a journal header to be written between the pages journaled by
    ** this function.
    */
    assert( !MEMDB );
    assert( (pPager->doNotSpill & SPILLFLAG_NOSYNC)==0 );
    pPager->doNotSpill |= SPILLFLAG_NOSYNC;

    /* This trick assumes that both the page-size and sector-size are
    ** an integer power of 2. It sets variable pg1 to the identifier
    ** of the first page of the sector pPg is located on.
    */
    pg1 = ((pPg->pgno-1) & ~(nPagePerSector-1)) + 1;

    nPageCount = pPager->dbSize;
    if( pPg->pgno>nPageCount ){
      nPage = (pPg->pgno - pg1)+1;
    }else if( (pg1+nPagePerSector-1)>nPageCount ){
      nPage = nPageCount+1-pg1;

    }else{
      nPage = nPagePerSector;
    }
    assert(nPage>0);
    assert(pg1<=pPg->pgno);
    assert((pg1+nPage)>pPg->pgno);

    for(ii=0; ii<nPage && rc==SQLITE_OK; ii++){
      Pgno pg = pg1+ii;
      PgHdr *pPage;
      if( pg==pPg->pgno || !sqlite3BitvecTest(pPager->pInJournal, pg) ){
        if( pg!=PAGER_MJ_PGNO(pPager) ){
          rc = sqlite3PagerGet(pPager, pg, &pPage);
          if( rc==SQLITE_OK ){
            rc = pager_write(pPage);
            if( pPage->flags&PGHDR_NEED_SYNC ){
              needSync = 1;
            }
            sqlite3PagerUnrefNotNull(pPage);
          }
        }
      }else if( (pPage = pager_lookup(pPager, pg))!=0 ){
        if( pPage->flags&PGHDR_NEED_SYNC ){
          needSync = 1;
        }
        sqlite3PagerUnrefNotNull(pPage);
      }
    }

    /* If the PGHDR_NEED_SYNC flag is set for any of the nPage pages 
    ** starting at pg1, then it needs to be set for all of them. Because
    ** writing to any of these nPage pages may damage the others, the
    ** journal file must contain sync()ed copies of all of them
    ** before any of them can be written out to the database file.
    */
    if( rc==SQLITE_OK && needSync ){
      assert( !MEMDB );
      for(ii=0; ii<nPage; ii++){
        PgHdr *pPage = pager_lookup(pPager, pg1+ii);
        if( pPage ){
          pPage->flags |= PGHDR_NEED_SYNC;
          sqlite3PagerUnrefNotNull(pPage);
        }
      }
    }

    assert( (pPager->doNotSpill & SPILLFLAG_NOSYNC)!=0 );
    pPager->doNotSpill &= ~SPILLFLAG_NOSYNC;
  }else{
    rc = pager_write(pDbPage);
  }
  return rc;
}

/*
** Return TRUE if the page given in the argument was previously passed
** to sqlite3PagerWrite().  In other words, return TRUE if it is ok
** to change the content of the page.
*/







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  /* Update the database size and return.
  */
  if( pPager->dbSize<pPg->pgno ){
    pPager->dbSize = pPg->pgno;
  }
  return rc;
}

/*
** This is a variant of sqlite3PagerWrite() that runs when the sector size
** is larger than the page size.  SQLite makes the (reasonable) assumption that
** all bytes of a sector are written together by hardware.  Hence, all bytes of
** a sector need to be journalled in case of a power loss in the middle of
** a write.
**
** Usually, the sector size is less than or equal to the page size, in which
** case pages can be individually written.  This routine only runs in the exceptional
** case where the page size is smaller than the sector size.
*/
static SQLITE_NOINLINE int pagerWriteLargeSector(PgHdr *pPg){
  int rc = SQLITE_OK;            /* Return code */
  Pgno nPageCount;               /* Total number of pages in database file */
  Pgno pg1;                      /* First page of the sector pPg is located on. */
  int nPage = 0;                 /* Number of pages starting at pg1 to journal */
  int ii;                        /* Loop counter */
  int needSync = 0;              /* True if any page has PGHDR_NEED_SYNC */
  Pager *pPager = pPg->pPager;   /* The pager that owns pPg */
  Pgno nPagePerSector = (pPager->sectorSize/pPager->pageSize);

  /* Set the doNotSpill NOSYNC bit to 1. This is because we cannot allow
  ** a journal header to be written between the pages journaled by
  ** this function.
  */
  assert( !MEMDB );
  assert( (pPager->doNotSpill & SPILLFLAG_NOSYNC)==0 );
  pPager->doNotSpill |= SPILLFLAG_NOSYNC;

  /* This trick assumes that both the page-size and sector-size are
  ** an integer power of 2. It sets variable pg1 to the identifier
  ** of the first page of the sector pPg is located on.
  */
  pg1 = ((pPg->pgno-1) & ~(nPagePerSector-1)) + 1;

  nPageCount = pPager->dbSize;
  if( pPg->pgno>nPageCount ){
    nPage = (pPg->pgno - pg1)+1;
  }else if( (pg1+nPagePerSector-1)>nPageCount ){
    nPage = nPageCount+1-pg1;
  }else{
    nPage = nPagePerSector;
  }
  assert(nPage>0);
  assert(pg1<=pPg->pgno);
  assert((pg1+nPage)>pPg->pgno);

  for(ii=0; ii<nPage && rc==SQLITE_OK; ii++){
    Pgno pg = pg1+ii;
    PgHdr *pPage;
    if( pg==pPg->pgno || !sqlite3BitvecTest(pPager->pInJournal, pg) ){
      if( pg!=PAGER_MJ_PGNO(pPager) ){
        rc = sqlite3PagerGet(pPager, pg, &pPage);
        if( rc==SQLITE_OK ){
          rc = pager_write(pPage);
          if( pPage->flags&PGHDR_NEED_SYNC ){
            needSync = 1;
          }
          sqlite3PagerUnrefNotNull(pPage);
        }
      }
    }else if( (pPage = pager_lookup(pPager, pg))!=0 ){
      if( pPage->flags&PGHDR_NEED_SYNC ){
        needSync = 1;
      }
      sqlite3PagerUnrefNotNull(pPage);
    }
  }

  /* If the PGHDR_NEED_SYNC flag is set for any of the nPage pages 
  ** starting at pg1, then it needs to be set for all of them. Because
  ** writing to any of these nPage pages may damage the others, the
  ** journal file must contain sync()ed copies of all of them
  ** before any of them can be written out to the database file.
  */
  if( rc==SQLITE_OK && needSync ){
    assert( !MEMDB );
    for(ii=0; ii<nPage; ii++){
      PgHdr *pPage = pager_lookup(pPager, pg1+ii);
      if( pPage ){
        pPage->flags |= PGHDR_NEED_SYNC;
        sqlite3PagerUnrefNotNull(pPage);
      }
    }
  }

  assert( (pPager->doNotSpill & SPILLFLAG_NOSYNC)!=0 );
  pPager->doNotSpill &= ~SPILLFLAG_NOSYNC;
  return rc;
}

/*
** Mark a data page as writeable. This routine must be called before 
** making changes to a page. The caller must check the return value 
** of this function and be careful not to change any page data unless 
** this routine returns SQLITE_OK.
**
................................................................................
** function also deals with the special case where 2 or more pages
** fit on a single disk sector. In this case all co-resident pages
** must have been written to the journal file before returning.
**
** If an error occurs, SQLITE_NOMEM or an IO error code is returned
** as appropriate. Otherwise, SQLITE_OK.
*/
int sqlite3PagerWrite(PgHdr *pPg){





  assert( (pPg->flags & PGHDR_MMAP)==0 );
  assert( pPg->pPager->eState>=PAGER_WRITER_LOCKED );
  assert( pPg->pPager->eState!=PAGER_ERROR );
  assert( assert_pager_state(pPg->pPager) );

  if( pPg->pPager->sectorSize > (u32)pPg->pPager->pageSize ){


























    return pagerWriteLargeSector(pPg);
  }else{













    return pager_write(pPg);


  }


































}

/*
** Return TRUE if the page given in the argument was previously passed
** to sqlite3PagerWrite().  In other words, return TRUE if it is ok
** to change the content of the page.
*/