数据|数据库
找了些时间，改进了自己文本数据库系统，从空间利用效率和并发性能两个方面着手，搞高了程序性能。
在空间利用率上，做了两点改进，一是在删除记录的时候，如果记录的存放位置在数据库的末端，就自动修改数据库末端指针，而不是将此记录的空间作为一个闲置块存入闲置块记录中，这样就可以继续在数据文件尾分配任意长度的空间而不是像以前那样将这个删除记录的空间整块分配给下一次请求空间的新记录；第二点改进是在从闲置块中请求空间的时候，不仅继续采用原来的最佳适应法，而且在请求到合适的闲置块的时候并不是将整个块而是将其部分划分给新记录，这样又进一部提高了空间的利用率。
在并发性能上，增加了数据库的打开模式这个选项。为了保持文本数据库操作的原子性，以前都以写模式打开数据库，用户无论是从数据库中读数据或写数据，系统都会锁定数据库而禁止其它用户并发的读写操作，而大多情况下，用户都是浏览网页而不是POST数据，禁止对数据库的并行的读操作，势必成为网页浏览速度的瓶颈，为了加速网页生成速度，在数据库中加入了打开模式这一选项，在只读模式下，可以允许不同的用户并发地从数据库中申请数据，使得网页并发性能得到了一定程序上的提高。
下面给出新文本数据库类的部分代码，其相关注释可以从原来的文章：http://202.113.13.169/site/redboy/index.php?item=read&id=1&blogID=4中获得。
源代码：
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class TxtDB
{
var $name='';//文本数据库名
var $path='';
var $minLen=20;
var $isError;
var $dbh;
var $indxh;
var $lfth;
var $lckh;
var $rcdCnt=0;
var $maxID=0;
var $leftCnt=0;
var $DBend=0;
var $mod='w';
function TxtDB($name,$mod='w',$path='bpns_dbm')
{
$this->name=$name;
$this->path=$path.'/'.$name;
$this->isError=0;
$this->mod=$mod;
$path=$this->path;
if ($name!='')
{
@mkdir($this->path,0777);
if (!file_exists($path.'/'.$name.'.tdb')) $this->dbh=fopen($this->path.'/'.$name.'.tdb','w+');
else $this->dbh=fopen($path.'/'.$name.'.tdb','r+');
if (!file_exists($path.'/'.$name.'.indx')) $this->indxh=fopen($this->path.'/'.$name.'.indx','w+');
else $this->indxh=fopen($path.'/'.$name.'.indx','r+');
if (!file_exists($path.'/'.$name.'.lft')) $this->lfth=fopen($this->path.'/'.$name.'.lft','w+');
else $this->lfth=fopen($this->path.'/'.$name.'.lft','r+');
if ($this->mod=='w')
{
$this->lckh=fopen($this->path.'/'.$name.'.lck','w');
flock($this->lckh,2);
fwrite($this->lckh,'lck');//lock the datebase
}
$rcd=$this->getRcd(0);
$this->rcdCnt=$rcd[id];
$this->maxID=$rcd[loc];
$this->DBend=$rcd[len];
$rcd=$this->getLeft(0);
$this->leftCnt=$rcd[loc];
}
else $this->isError=1;
}
function setRcd($rid,$id,$loc,$len)
{
fseek($this->indxh,$rid*12);
$str=pack('III',$id,$loc,$len);
fwrite($this->indxh,$str,12);
}
function getRcd($rid)
{
fseek($this->indxh,$rid*12);
$str=fread($this->indxh,12);
$rcd=array();
$rcd[id]=str2int($str);
$rcd[loc]=str2int(substr($str,4,4));
$rcd[len]=str2int(substr($str,8,4));
return $rcd;
}
function setLeft($lid,$loc,$len)
{
fseek($this->lfth,$lid*8);
$str=pack('II',$loc,$len);
fwrite($this->lfth,$str,8);
}
function getLeft($lid)
{
fseek($this->lfth,$lid*8);
$str=fread($this->lfth,8);
$rcd[loc]=str2int($str);
$rcd[len]=str2int(substr($str,4,4));
return $rcd;
}
function clear()
{
$this->setRcd(0,0,0,0);
$this->setLeft(0,0,0);
}
function close()
{
@fclose($this->dbh);
@fclose($this->indxh);
@fclose($this->lfth);
@fclose($this->lckh);
}
function seekSpace($len)
{
$res=array('loc'=>0,'len'=>0);
if ($this->leftCnt $find=0;
$min=1000000;
for ($i=$this->leftCnt;$i>0;$i--)
{
$res=$this->getLeft($i);
if ($res[len]==$len) {$find=$i;break;}
else if($res[len]>$len)
{
if ($res[len]-$len {
$min=$res[len]-$len;
$find=$i;
}
}
}
if ($find)
{
$res=$this->getLeft($find);
if ($res[len] {
fseek($this->lfth,($find+1)*8);
$str=fread($this->lfth,($this->leftCnt-$find)*8);
fseek($this->lfth,$find*8);
fwrite($this->lfth,$str);
$this->leftCnt--;
$this->setLeft(0,$this->leftCnt,0);
return $res;
}
else
{
$rs=array();
$rs[loc]=$res[loc];
$rs[len]=$len;
$res[loc]+=$len;
$this->setLeft($find,$res[loc],$res[len]-$len);
return $rs;
}
}
else//fail
{
$res[len]=0;
return $res;
}
}
function insert($content,$len=0)//return with record id
{
$res=array('loc'=>0);
if ($this->mod!='w') return 0;
if (!$len) $len=strlen($content);
if ($lenminLen) $len=$this->minLen;
if ($this->leftCnt) $res=$this->seekSpace($len);
if (!$res[len])
{
$res[loc]=$this->DBend;
$res[len]=$len;
}
if ($res[loc]+$res[len]>$this->DBend) $this->DBend=$res[loc]+$res[len];
//echo $this->DBend.'
';
$this->maxID++;
$this->rcdCnt++;
$this->setRcd(0,$this->rcdCnt,$this->maxID,$this->DBend);
$this->setRcd($this->rcdCnt,$this->maxID,$res[loc],$res[len]);
fseek($this->dbh,$res[loc]);
fwrite($this->dbh,$content,$len);
return $this->maxID;
}
function findByID($id)
{
if ($id$this->maxID or $this->rcdCnt $left=1;
$right=$this->rcdCnt;
while($left {
$mid=(int)(($left+$right)/2);
if ($mid==$left or $mid==$right) break;
$rcd=$this->getRcd($mid);
if ($rcd[id]==$id) return $mid;
else if($id else $left=$mid;
}
//$rcd=$this->getRcd($mid);
//if ($rcd[id]==$id) return $mid;
$rcd=$this->getRcd($left);
if ($rcd[id]==$id) return $left;
$rcd=$this->getRcd($right);
if ($rcd[id]==$id) return $right;
return 0;
}
function delete($id)
{
if ($this->mod!='w') return 0;
$rid=$this->findByID($id);
if (!$rid) return;
$res=$this->getRcd($rid);
fseek($this->indxh,($rid+1)*12);
$str=fread($this->indxh,($this->rcdCnt-$i)*12);
fseek($this->indxh,$rid*12);
fwrite($this->indxh,$str);
$this->rcdCnt--;
if ($res[loc]+$res[len]==$this->DBend)
{
$this->DBend=$res[loc];
$this->setRcd(0,$this->rcdCnt,$this->maxID,$this->DBend);
}
else
{
$this->setRcd(0,$this->rcdCnt,$this->maxID,$this->DBend);
$this->leftCnt++;
$this->setLeft(0,$this->leftCnt,0);
$this->setLeft($this->leftCnt,$res[loc],$res[len]);
}
}
function update($id,$newcontent,$len=0)
{
if ($this->mod!='w') return;
$rid=$this->findByID($id);
if (!$rid) return;
if (!$len) $len=strlen($newcontent);
$rcd=$this->getRcd($rid);
if ($rcd[len] {
$this->leftCnt++;
$this->setLeft(0,$this->leftCnt,0);
$this->setLeft($this->leftCnt,$rcd[loc],$rcd[len]);
$rcd[loc]=$this->DBend;
$rcd[len]=$len;
$this->DBend+=$len;
$this->setRcd(0,$this->rcdCnt,$this->maxID,$this->DBend);
$this->setRcd($rid,$rcd[id],$rcd[loc],$rcd[len]);
}
fseek($this->dbh,$rcd[loc]);
fwrite($this->dbh,$newcontent,$len);
//echo $id.'
'.$content.'
'.$len;
}
function selectByRid($rid)
{
$res=array('id'=>0,'content'=>'');
if ($rid$this->rcdCnt) return $res;
else $rcd=$this->getRcd($rid);
$res[id]=$rcd[id];
$res[len]=$rcd[len];
fseek($this->dbh,$rcd[loc]);
$res[content]=fread($this->dbh,$rcd[len]);
//$res[rid]=$rid;
return $res;
}
function select($id)
{
return $this->selectByRid($this->findByID($id));
}
function backup()
{
copy($this->path.'/'.$this->name.'.tdb',$this->path.'/'.$this->name.'.tdb.bck');
copy($this->path.'/'.$this->name.'.indx',$this->path.'/'.$this->name.'.indx.bck');
copy($this->path.'/'.$this->name.'.lft',$this->path.'/'.$this->name.'.lft.bck');
}
function recover()
{
copy($this->path.'/'.$this->name.'.tdb.bck',$this->path.'/'.$this->name.'.tdb');
copy($this->path.'/'.$this->name.'.indx.bck',$this->path.'/'.$this->name.'.indx');
copy($this->path.'/'.$this->name.'.lft.bck',$this->path.'/'.$this->name.'.lft');
}
}
?>
PS: 其他可以参考上一篇文章：http://blog.csdn.net/heiyeshuwu/archive/2006/06/16/804265.aspx
