Using svnsync to mirror a google - Eli - Using svnsync to mirror a

20 Linux System Monitoring Tools Every SysAdmin Should Know
top, vmstats, w, uptime, ps, everything you need to know to monitor linux server performance

SQL Injection Attack
Presentation of SQL injection attacks, and how to prevent them in your code

Asynchronous/parallel HTTP requests using PHP multi_curl
How to work with web services with asynchronous/parallel requests using curl and curl_multi*

Even Faster Web Sites
How to optimize the loading of js, css, resources in your page, using cache and various HTML options

mk query digest
Perl profiler for memcached

Here a simple example on how using cas() command from PECL Memcached to update data that must be at all time up to date

In Memcached, series of commands are not atomic :

A series of commands is not atomic. If you issue a 'get' against an item, operate on the data, then wish to 'set' it back into memcached, you are not guaranteed to be the only process working on that value. In parallel, you could end up overwriting a value set by something else.

But PECL Memcached come with a useful function : cas()

The principle is :

• Make a get() to get a key value and a cas token (checksum of the value that the get return)
• Make some update on the value
• Ask memcached to update the value with cas() method with the cas token as parameter, to let memcached see if the actual value of the key you want to update is the same as he give before or if another script has changed it

Here the code example, we update an index array, adding values in it when not present

# Initializing Memcached connection
$memcache = new Memcached();
$memcache->addServer('localhost', 11211);
 
$indexKey = 'Our index key';
$newValue = 'Some new value to add to index';
$cas = null;
 
# Starting index updating
do 
{
  # Getting data, with parameter $cas to get as we want a cas token
  $indexData = $memcache->get($indexKey, null, $cas);
 
  # Index does not exists, initializing it
  if($indexData === false)
  {
    $indexData = array($newValue);
    $memcache->add($indexKey, $data, 1800);
  }
  # Index exists, updating it
  else
  {
    # Adding new value in index
    $indexData[] = $newValue;
    $memCache->cas($cas, $indexKey, $indexData, 1800);
  }
}
# If result is not stored, or data was updated by another thread
while(($memCache->getResultCode() == Memcached::RES_NOTSTORED) 
      || ($memCache->getResultCode() == Memcached::RES_DATA_EXISTS));

With that little script, we are sure that :

• If no index are present at start of our script but the index is created in another thread, we retrieve it before adding our value because we use the add() command (Memcached::RES_NOTSTORED)
• If the index is modified by another script while we are working on it, we get the up to date version before trying to add our new data, thanks to the cas() method (Memcached::RES_DATA_EXISTS)

Remember to be careful with cas(), under heavy concurrent updates, the do ... while() can easily take a lot of execution time, you must add a maximum try count break condition.

And remember to not check command success in a while loop with something like

$memCache->getResultCode() != Memcached::RES_SUCCESS

Memcached::RES_SERVER_ERROR or anything like this and your script will loop forever

Excellent quick reference card for Subversion 1.6 the version control system.

Grab it from http://www.collab.net/community/subversion/articles/CollabNet_SVNQuickReferenceCard.pdf

New version is released and available from http://code.google.com/p/phpmemcacheadmin/ and is now compatible with Memcached 1.4.5

Release Notes

• Added the reclaimed stats and reclaimed rate (New in Memcached 1.4.5)
• Added the eviction rate
• Added a "Are you sure ?" for flush_all command
• Fixed the eviction rate bug on live stats
• Fixed the PECL Memcache/Memcached API bug with get commands
• Fixed the flush_all link not working from slabs stats

If you have any suggestion or bugs, you can contact me by mail

How to install & run memcached 1.4.4 on Windows

1. Download package from http://labs.northscale.com/memcached-packages/
2. Unzip to your desired directory (c:\memcached_win32\ in my example)

Add memcached to the Windows services from the command line

c:\memcached_win32\memcached.exe -d install

Then you can start or stop the memcached server as a service with

net start memcached
net stop memcached

To edit the memcached server configuration, open regedit and go to HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\memcached, then find and edit the ImagePath

"C:\memcached_win32\memcached.exe" -d runservice -m 256 -p 11210

Example running memcached with 256 M and on port 11210

Using memcached telnet interface

You can communicate with memcached server (localhost or distant) by opening a telnet session.

Memcached text protocol can be found here about Protocol

It's a bit confusing, but here some examples

Connecting to server :

> telnet localhost 11211

Server stats :

> stats
STAT pid 14550
STAT uptime 2530
[a lot of line...]
END

Slabs stats :

> stats slabs
STAT 1:chunk_size 80
[a lot of line...]
END

Items stats :

> stats items
STAT items:1:number 1
[a lot of line...]
END

Set command :

> set key 0 900 13
> data_to_store
STORED

Details on set command :

set <key> <flags> <exptime> <bytes> with <bytes> = number of bytes of data you want to store.

Get command :

> get
END
> get key
VALUE key 0 13
data_to_store
END

Increment & decrement commands :

> set key 0 900 2
> 10
STORED
> incr key 5
15
> decr key 2
13
> get key
VALUE key 0 2
13

You can also use phpMemCacheAdmin to execute these command and monitor your queries