How to save session to memcached in php? How to save php session distributedly

session_set_save_handler has nothing to do with memcached's method of saving session

On the memcached server

1) Download memcached

#wget http://memcached.googlecode.com/files/memcached-1.4.15.tar.gz

2) Since memcached depends on libevent, you need to install the libevent library first. Here is the direct yum installation

#yum install *libevent*

3) Install memcached

#./configure --prefix=/usr/local/memcached
#make
# make install

4) Start memcached

#/usr/local/memcached/bin/memcached -d -m 4096 -p 11211 -u root
-d daemon ?-p port -u ?user -m memory

in On the web server server

5) Install the php memcache module on the web server

#/usr/local/php/bin/pecl install memcache

Enable memcache session handler support? [yes] : yes (select yes here)

6) Add the following content to php.ini:

extension=/usr/local/php/lib/php/extensions/no-debug-non-zts-20090626/memcache.so

7) Modify php. The session.save_handler and session.save_path in ini are as follows:

session.save_handler = memcache
session.save_path = "tcp://memcached server ip:11211"

It can also be used in PHP programs

ini_set(' session.save_handler', 'memcache');
ini_set('session.save_path', 'tcp://memcached server ip:11211');

Note: This way of using memcached to save the session has nothing to do with session_set_save_handler

After installing memcached

modify session.save_handler to memcache in php.ini, and modify save_path to point to the address and port of memcached

session.save_handler = memcache

session.save_path = tcp://127.0 .0.1:11211

memcache’s PECL extension is very powerful and can support failover and distributed storage.

The method of use is very simple, just use commas to separate each memcached server in the parameter list of session.save_path, such as:

session.save_path = "tcp://172.16.8.81:11211,tcp://172.16. 8.82:11211,tcp://172.16.8.83:11211"

The saved session will be hashed and then saved to each memcached server. Memcache supports two hash algorithms, crc32 and fnv:

memcache.hash_function= {crc32,fnv}

The fnv algorithm is rarely mentioned in the document. It is said that its hashing is better than crc32. However, after I experimented with the following small program, I found that the hashing algorithm of crc32 is still more distributed. average.

<?php
ini_set("memcache.hash_function", "crc32");
$memcache = new Memcache;
$memcache1 = new Memcache;
$memcache2 = new Memcache;
$memcache->addServer(&#39;localhost&#39;, 11211);
$memcache->addServer(&#39;localhost&#39;, 11212);
$memcache->flush();
$memcache1->connect(&#39;localhost&#39;, 11211);
$memcache2->connect(&#39;localhost&#39;, 11212);
$fp1 = fopen("mem1.txt", "w");
$fp2 = fopen("mem2.txt", "w");
for ($i = 0; $i < 1000; $i++)
{
$memcache->set($i, $i, 0, 1000);
fwrite($fp1, $memcache1->get($i) . " ");
fwrite($fp2, $memcache2->get($i) . " ");
}
fclose($fp1);
fclose($fp2);

Then I tested the session saving

I opened 3 memcached processes for testing

<?php
ini_set("memcache.hash_function", "fnv");
ini_set("error_reporting", "E_CORE_ERROR");
$memcache1 = new Memcache;
$memcache1->connect(&#39;localhost&#39;, 11211);
$memcache1->flush();
$memcache2 = new Memcache;
$memcache2->connect(&#39;localhost&#39;, 11212);
$memcache2->flush();
$memcache3 = new Memcache;
$memcache3->connect(&#39;localhost&#39;, 11213);
$memcache3->flush();
$fp1 = fopen(&#39;mem1.txt&#39;, &#39;w&#39;);
$fp2 = fopen(&#39;mem2.txt&#39;, &#39;w&#39;);
$fp3 = fopen(&#39;mem3.txt&#39;, &#39;w&#39;);
for ($i = 0; $i < 1000; $i++)
{
session_start();
$ssid = session_id();
echo $ssid;
session_register("id");
$_SESSION["id"] = $ssid;
session_write_close();
fwrite($fp1, $memcache1->get($ssid) . &#39; &#39;);
fwrite($fp2, $memcache2->get($ssid) . &#39; &#39;);
fwrite($fp3, $memcache3->get($ssid) . &#39; &#39;);
//session_destroy();
}
fclose($fp1);
fclose($fp2);
fclose($fp3);

The strange thing is that memcached2 is usually not selected,

and the contents of 1 and 3 are consistent. It may be for failover,

And when I turn off 1 and 3, content will appear in 2, indicating that memcached2 is working normally.

This phenomenon exists regardless of whether my hashing algorithm uses crc32 or fnv.

Finally I found out: there is a problem with this test program.

Because after session_write_close, the session of the entire program is unique.

That is, although the loop has been looped so many times, including the session_destroy call, the session id returned is the same.

This results in the content in the two files being consistent but the other file having no content.

Based on this,

I can only call the script in batches. The script is modified as follows:

<?php
ini_set("memcache.hash_strategy", "consistent");
ini_set("memcache.hash_function", "crc32");
ini_set("error_reporting", "E_CORE_ERROR");
ini_set("memcache.allow_failover", "0");
$memcache1 = new Memcache;
$memcache1->connect(&#39;localhost&#39;, 10001);
$memcache1->flush();
$memcache2 = new Memcache;
$memcache2->connect(&#39;localhost&#39;, 10002);
$memcache2->flush();
$memcache3 = new Memcache;
$memcache3->connect(&#39;localhost&#39;, 10003);
$memcache3->flush();
$fp1 = fopen("mem1.txt", "a+");
$fp2 = fopen("mem2.txt", "a+");
$fp3 = fopen("mem3.txt", "a+");
session_start();
$ssid = session_id();
echo $ssid . "\n";
session_register("id");
$_SESSION["id"] = $ssid;
//session_destroy();
session_write_close();
fwrite($fp1, $memcache1->get($ssid) . " ");
fwrite($fp2, $memcache2->get($ssid) . " ");
fwrite($fp3, $memcache3->get($ssid) . " ");
session_destroy();
fclose($fp1);
fclose($fp2);
fclose($fp3);

Then run it repeatedly in the shell. Multiple times, the returned ID is different.

Open the mem*.txt file again to view,

found that among the 3 files, each session will be saved in two of the files, and then the distribution is different.

This proves that memcache is used to save sessions. One is to achieve failover, and the second is to do hash distribution and save according to session id.