Dutch php conference_apc_mem2010

APC & Memcache the High
Performance Duo
Dutch PHP Conference 2010

Ilia Alshanetsky
http://ilia.ws/

1

What is APC?

• Alternative PHP Cache
• Primarily designed to accelerate script
performance via opcode caching

• Extends opcode caching to facilitate user-data
caching

• Actively maintained & well supported

2

Opcode Caching
Default Mode With APC
PHP Script
PHP Script

APC
Opcode Cache

Zend Compile

Zend Compile No Data Cached?

Zend Execute
Yes
Cache Opcode

Function/Method
Require/Include
Call Zend Execute

Function/Method
Require/Include
Call

3

APC User-Cache

• Allows you to apply the same caching logic to
your data as applied to PHP scripts.

Slide Motto:
Not everything has to be real-time!

4

APC in Practice
// store an array of values for 1 day, referenced by "identifier"
if (!apc_add("identifier", array(1,2,3), 86400)) {
    // already exists? let's update it instead
    if (!apc_store("identifier", array(1,2,3), 86400)) {
        // uh, oh, b0rkage
    }
}

$ok = null;
// fetch value associated with "identified" and
// put success state into $ok variable
$my_array = apc_fetch("identifier", $ok);
if ($ok) {
    // changed my mind, let's delete it
    apc_delete("identifier");
}

5

Let’s be lazy

// create or update an array of values for 1 day
if (!apc_store("identifier", array(1,2,3), 86400)) {
// uh, oh, b0rkage
mail("gopal, brian, kalle", "you broke my code", "fix it!");
}

If you don’t care whether your are adding or updating
values you can just use apc_store() and keep your
code simpler

6

Don’t Delete
• Deleting from cache is expensive as it may need
to re-structure internal hash tables.

• Rely on auto-expiry functionality instead
• Or an oﬀ-stream cron job to clean up stale
cache entries

• In many cases it is simpler just to start from
scratch.

apc_clear_cache(“user”)

7

Installing APC
# Unix

sudo bash (open root shell)

pecl install apc (configure, compile & install APC)

# Windows

Copy the php_apc.dll file into your php’s ext/
directory

# Common

Enable APC from your php.ini file

8

Advantages of APC

• If you (or your ISP) uses opcode caching,
chances are it is already there.

• Really eﬃcient at storing simple types (scalars
& arrays)

• Really simple to use, can’t get any easier…
• Fairly stable

9

APC Limitations

• PHP only, can’t talk to other “stuﬀ ”
• Not distributed, local only
• Opcode + User cache == all eggs in one basket
• Could be volatile

10

Memcached

• Interface to Memcached - a distributed caching
system

• Provides Object Oriented interface to caching
system

• Oﬀers a built-in session handler
• Can only be used for “user” caching
• Purpose built, so lots of nifty features

11

Memcache vs Memcached

• Memcached Advantages
• Faster
• Igbinary serializer
• fastlz compression
• Multi-Server Interface
• Fail-over callback support

12

Basics in Practice
$mc = new MemCached();

// connect to memcache on local machine, on default port
$mc->addServer('localhost', '11211');

// try to add an array with a retrieval key for 1 day
if (!$mc->add('key', array(1,2,3), 86400)) {
    // if already exists, let's replace it
    if ($mc->replace('key', array(1,2,3), 86400)) {
        die("Critical Error");
    }
}

// let's fetch our data
if (($data = $mc->get('key')) !== FALSE) {
    // let's delete it now
    $mc->delete('key'); // RIGHT NOW!
}

13

Data Retrieval Gotcha(s)

$mc->add('key', 0);

if (!($data = $mc->get('key'))) {
die("Not Found?"); // not true
// The value could be 0,array(),NULL,””
// always compare Memcache::get() result to
// FALSE constant in a type-sensitive way (!== FALSE)
}

// The “right” way!
die("Not Found");
}

14

Data Retrieval Gotcha(s)

$mc->add('key', FALSE);

die("Not Found?"); // not true
// The value could be FALSE, you
// need to check the response code
}

// The “right” way!
if (
(($data = $mc->get('key')) !== FALSE)
&&
($mc->getResultCode() != MemCached::RES_SUCCESS)
) {
die("Not Found");
}

15

Interface Basics Continued...
// on local machine we can connect via Unix Sockets for better speed
$mc->addServer('/var/run/memcached/11211.sock', 0);

// add/or replace, don't care just get it in there
// without expiration parameter, will remain in cache “forever”
$mc->set('key1', array(1,2,3));

$key_set = array('key1' => “foo”, 'key1' => array(1,2,3));

// store multiple keys at once for 1 hour
$mc->setMulti($key_set, 3600);

// get multiple keys at once
$data = $mc->getMulti(array_keys($key_set));
/*
array( For multi-(get|set), all ops
'key1' => ‘foo’
'key2' => array(1,2,3) must succeed for
)
*/
successful return.
16

Multi-Server Environment


// add multiple servers to the list
// as many servers as you like can be added
$mc->addServers(
array('localhost', 11211, 80), // high-priority 80%
array('192.168.1.90', 11211, 20)// low-priority 20%
);

// You can also do it one at a time, but this is not recommended
$mc->addServer('localhost', 11211, 80);
$mc->addServer('192.168.1.90', 11211, 20);

// Get a list of servers in the pool
$mc->
getServerList();
// array(array(‘host’ => … , ‘port’ => … ‘weight’ => …))

17

Data Segmentation
• Memcached interface allows you to store
certain types of data on speciﬁc servers
$mc->addServers( … );

// Add data_key with a value of “value” for 10 mins to server
// identified by “server_key”
$mc->addByKey('server_key', 'data_key', 'value', 600);

// Fetch key from specific server
$mc->getByKey('server_key', 'data_key');

// Add/update key on specific server
$mc->setByKey('server_key', 'data_key', 'value', 600);

// Remove key from specific server
$mc->deleteByKey('server_key', 'data_key');

18

And there is more ...
• The speciﬁc-server interface also supports multi-(get|set)

$mc->addServers( … );

$key_set = array('key1' => “foo”, 'key1' => array(1,2,3));

// store multiple keys at once for 1 hour
$mc->setMultiByKey('server_key', $key_set, 3600);

// get multiple keys at once
$data = $mc->getMultiByKey('server_key', array_keys($key_set));

19

Delayed Data Retrieval

• One of the really neat features of Memcached
extension is the ability to execute the “fetch”
command, but defer the actual data retrieval
until later.

• Particularly handy when retrieving many keys
that won’t be needed until later.

20

Delayed Data Retrieval


$mc->getDelayed(array('key')); // parameter is an array of keys

/* some PHP code that does “stuff” */

// Fetch data one record at a time
while ($data = $mc->fetch()) { ... }

// Fetch all data in one go
$data = $mc->fetchAll();

21

Atomic Counters
$mc->addServer('localhost', 11211);

// initialize counter to 1
$mc->set('my_counter', 1);

// increase count by 1
$mc->increment('my_counter');

// increase count by 10
$mc->increment('my_counter', 10);

// decrement count by 1
$mc->decrement('my_counter');

// decrement count by 10
$mc->decrement('my_counter', 10);

22

Counter Trick

// add key position if does not already exist
if (!$mc->add('key_pos', 1)) {
    // otherwise increment it
    $position = $mc->increment('key_pos');
} else {
    $position = 1;
}

// add real value at the new position
$mc->add('key_value_' . $position, array(1,2,3));

• Simpliﬁes cache invalidation
• Reduces lock contention (or eliminates it)
23

Data Compression
• In many cases performance can be gained by
compressing large blocks of data. Since in most cases
network IO is more expensive then CPU speed + RAM.
// enable compression
$mc->setOption(Memcached::OPT_COMPRESSION, TRUE);

Related INI settings (INI_ALL)
Other possible value is zlib
memcached.compression_type=fastlz

minimum compression rate
memcached.compression_factor=1.3

minimum data size to compress
memcached.compression_threshold=2000

24

PHP Serialization

If you are using memcached to store complex data type
(arrays & objects), they will need to be converted to
strings for the purposes of storage, via serialization.

Memcached can make use of igbinary serializer that
works faster (~30%) and produces more compact data set
(up-to 45% smaller) than native PHP serializer.

http://github.com/phadej/igbinary

25

Enabling Igbinary
Install Memcached extension with
--enable-memcached-igbinary


// use Igbinary serializer
$mc->setOption(
Memcached::OPT_SERIALIZER,
Memcached::SERIALIZER_IGBINARY
);

26

Utility Methods
Array
(

[server:port]
=>
Array

(

[pid]
=>
4933

[uptime]
=>
786123

[threads]
=>
1

[time]
=>
1233868010

[pointer_size]
=>
32
// memcached statistics gathering

[rusage_user_seconds]
=>
0

[rusage_user_microseconds]
=>
140000
$mc->getStats();

[rusage_system_seconds]
=>
23

[rusage_system_microseconds]
=>
210000

[curr_items]
=>
145

[total_items]
=>
2374

[limit_maxbytes]
=>
67108864

[curr_connections]
=>
2

[total_connections]
=>
151
// clear all cache entries

[a]
=>
3
$mc->flush();

[bytes]
=>
20345

[cmd_get]
=>
213343

[cmd_set]
=>
2381
// clear all cache entries

[get_hits]
=>
204223
// in 10 minutes

[get_misses]
=>
9120
$mc->flush(600);

[evictions]
=>
0

[bytes_read]
=>
9092476

[bytes_written]
=>
15420512

[version]
=>
1.2.6

)
)
27

Installing Memcached

Download memcached from http://
www.memcached.org and compile it.

Download libmemcached from http://tangent.org/552/
libmemcached.html and compile it.

pecl install memcached (conﬁgure, make, make install)

Enable Memcached from your php.ini ﬁle

28

Memcached Session Handler

# Session settings

session.save_handler # set to “memcached

session.save_path # set to memcache host server:port

memcached.sess_prefix # Defaults to memc.sess.key.

# Locking Controls

# Whether to enable session lock, on by default
memcached.sess_locking

# Maximum number of microseconds to wait on a lock
memcached.sess_lock_wait

29

Advantages of Memcache

• Allows other languages to talk to it
• One instance can be shared by multiple servers
• Failover & redundancy
• Nifty Features
• Very stable

30

It is not perfect because?

• Slower then APC, especially for array storage
• Requires external daemon
• You can forget about it on
shared hosting

31

That’s all folks

Any Questions?

Slides at: http://ilia.ws
Comments: http://joind.in/1554
32

APC Conﬁguration

apc.enable # enable APC
apc.enable_cli # enable for CLI sapi
apc.max_file_size # max PHP file to be cached
apc.stat # turn off ONLY if your files never change
apc.file_update_protection # good idea if you edit files on
live environment

apc.filters # posix (ereg) expressions to filter out files
from being cached

apc.mmap_file_mask # /tmp/apc.XXXXXX (use mmap IO, USE IT!)
apc.shm_segments # if not using mmap IO, otherwise 1
apc.shm_size # how much memory to use

33

Make PHBs Happy

✴ Pretty graphics require GD extension

• For raw data you can use the apc_cache_info()
and apc_sma_info() functions.
34

Dutch php conference_apc_mem2010

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