php的session默認(rèn)是以文件方式保存在服務(wù)器端，并且在客戶端使用cookie保存變量，這就會出現(xiàn)一個問題，當(dāng)一個用戶由于某種安全原因關(guān)閉了瀏覽器的cookie，程序中的session相關(guān)操作將無法執(zhí)行。因此，如果能以數(shù)據(jù)庫保存session數(shù)據(jù)，將不受客戶端設(shè)置的限制，并且在性能和擴展性等方面有一個飛躍。程序中使用關(guān)鍵函數(shù)是session_set_save_handler，同時要將php.ini里的session.save_handler = files 改為 user。這里我們討論的環(huán)境是linux(freesd)+apache+mysql+php。
數(shù)據(jù)表結(jié)構(gòu)：[sessions]
create table sessions (
sesskey char(32) not null,
expiry int(11) unsigned not null,
value text not null,
primary key (sesskey)
);
程序代碼：[session_inc.php]
<?php
$sess_dbhost = "yourhost"; /* database server hostname */
$sess_dbname = "yourdb"; /* database name */
$sess_dbuser = "youruser"; /* database user */
$sess_dbpass = "yourpassword"; /* database password */
$sess_dbh = "";
$sess_life = get_cfg_var("session.gc_maxlifetime");
function sess_open($save_path, $session_name) {
global $sess_dbhost, $sess_dbname, $sess_dbuser, $sess_dbpass, $sess_dbh;
if (! $sess_dbh = mysql_pconnect($sess_dbhost, $sess_dbuser, $sess_dbpass)) {
echo "<li>can't connect to $sess_dbhost as $sess_dbuser";
echo "<li>mysql error: " . mysql_error();
die;
}
if (! mysql_select_db($sess_dbname, $sess_dbh)) {
echo "<li>unable to select database $sess_dbname";
die;
}
return true;
}
function sess_close() {
return true;
}
function sess_read($key) {
global $sess_dbh, $sess_life;
$qry = "select value from session_tbl where sesskey = '$key' and expiry > " . time();
$qid = mysql_query($qry, $sess_dbh);
if (list($value) = mysql_fetch_row($qid)) {
return $value;
}
return false;
}
function sess_write($key, $val) {
global $sess_dbh, $sess_life;
$expiry = time() + $sess_life; //過期時間
$value = addslashes($val);
$qry = "insert into session_tbl values ('$key', $expiry, '$value')";
$qid = mysql_query($qry, $sess_dbh);
if (! $qid) {
$qry = "update session_tbl set expiry = $expiry, value = '$value' where sesskey = '$key' and expiry > " . time();
$qid = mysql_query($qry, $sess_dbh);
}
return $qid;
}
function sess_destroy($key) {
global $sess_dbh;
$qry = "delete from session_tbl where sesskey = '$key'";
$qid = mysql_query($qry, $sess_dbh);
return $qid;
}
function sess_gc($maxlifetime) {
global $sess_dbh;
$qry = "delete from session_tbl where expiry < " . time();
$qid = mysql_query($qry, $sess_dbh);
return mysql_affected_rows($sess_dbh);
}
session_set_save_handler(
"sess_open",
"sess_close",
"sess_read",
"sess_write",
"sess_destroy",
"sess_gc");
session_start();
?>
完成以上步驟后，在程序中使用require("session_inc.php")來代替session_start()即可，其他的session函數(shù)還是象以前一樣的方法調(diào)用。
