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Overview
Comment:The MEMSYS5 algorithm does not have to return the block with the lowest address. Any block of the appropriate size will do. Use the first block found on the freelist for the appropriate size for a performance improvement.
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SHA1:12e612e8e7c4a6f83acf0daf5608151fb5ec1575
User & Date: drh 2013-11-24 00:46:00
Context
2013-11-24
01:14
Add the --scratch parameter to speedtest1. Improved error messages when misconfiguring memory parameters in speedtest1. check-in: 8f3c767a user: drh tags: trunk
00:46
The MEMSYS5 algorithm does not have to return the block with the lowest address. Any block of the appropriate size will do. Use the first block found on the freelist for the appropriate size for a performance improvement. check-in: 12e612e8 user: drh tags: trunk
2013-11-23
22:45
A much simpler fix is to simply change MEMSYS5 so that it takes any free block of the appropriate size (the first on the list of free blocks) rather than searching for the one with the smallest address. This is also faster than using the min-heap algorithm. Need to research to verify that the allocator still satisfies the Robson proof, however. Closed-Leaf check-in: 8191b512 user: drh tags: memsys5-performance
21:29
Add newlines at the end of some error messages in speedtest1. check-in: 6b98f0af user: drh tags: trunk
Changes
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Changes to src/mem5.c.

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    int i = ((u8 *)p-mem5.zPool)/mem5.szAtom;
    assert( i>=0 && i<mem5.nBlock );
    iSize = mem5.szAtom * (1 << (mem5.aCtrl[i]&CTRL_LOGSIZE));
  }
  return iSize;
}

/*
** Find the first entry on the freelist iLogsize.  Unlink that
** entry and return its index. 
*/
static int memsys5UnlinkFirst(int iLogsize){
  int i;
  int iFirst;

  assert( iLogsize>=0 && iLogsize<=LOGMAX );
  i = iFirst = mem5.aiFreelist[iLogsize];
  assert( iFirst>=0 );
  while( i>0 ){
    if( i<iFirst ) iFirst = i;
    i = MEM5LINK(i)->next;
  }
  memsys5Unlink(iFirst, iLogsize);
  return iFirst;
}

/*
** Return a block of memory of at least nBytes in size.
** Return NULL if unable.  Return NULL if nBytes==0.
**
** The caller guarantees that nByte is positive.
**
** The caller has obtained a mutex prior to invoking this
................................................................................
  */
  for(iBin=iLogsize; mem5.aiFreelist[iBin]<0 && iBin<=LOGMAX; iBin++){}
  if( iBin>LOGMAX ){
    testcase( sqlite3GlobalConfig.xLog!=0 );
    sqlite3_log(SQLITE_NOMEM, "failed to allocate %u bytes", nByte);
    return 0;
  }

  i = memsys5UnlinkFirst(iBin);
  while( iBin>iLogsize ){
    int newSize;

    iBin--;
    newSize = 1 << iBin;
    mem5.aCtrl[i+newSize] = CTRL_FREE | iBin;
    memsys5Link(i+newSize, iBin);







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    int i = ((u8 *)p-mem5.zPool)/mem5.szAtom;
    assert( i>=0 && i<mem5.nBlock );
    iSize = mem5.szAtom * (1 << (mem5.aCtrl[i]&CTRL_LOGSIZE));
  }
  return iSize;
}




















/*
** Return a block of memory of at least nBytes in size.
** Return NULL if unable.  Return NULL if nBytes==0.
**
** The caller guarantees that nByte is positive.
**
** The caller has obtained a mutex prior to invoking this
................................................................................
  */
  for(iBin=iLogsize; mem5.aiFreelist[iBin]<0 && iBin<=LOGMAX; iBin++){}
  if( iBin>LOGMAX ){
    testcase( sqlite3GlobalConfig.xLog!=0 );
    sqlite3_log(SQLITE_NOMEM, "failed to allocate %u bytes", nByte);
    return 0;
  }
  i = mem5.aiFreelist[iBin];
  memsys5Unlink(i, iBin);
  while( iBin>iLogsize ){
    int newSize;

    iBin--;
    newSize = 1 << iBin;
    mem5.aCtrl[i+newSize] = CTRL_FREE | iBin;
    memsys5Link(i+newSize, iBin);