Caching and tuning fun for high scalability @ FrOSCon 2011

Caching and tuning fun for high scalability Wim Godden Cu.be Solutions

Notes about this presentation
This presentation was part of the FrOSCon 2011 program. It was designed to presented live and as a result many of the slides may seem odd without spoken explanation. The live benchmarks at the conference are ofcourse also not part of these slides.

Who am I ?
Wim Godden (@wimgtr)
Owner of Cu.be Solutions (http://cu.be)
PHP developer since 1997
Developer of OpenX
Zend Certified Engineer
Zend Framework Certified Engineer
MySQL Certified Developer

Who are you ?
Developers ?
System/network engineers ?
Managers ?
Caching experience ?

Caching and tuning fun for high scalability Wim Godden Cu.be Solutions

Goals of this tutorial
Everything about caching and tuning
A few techniques
How-to
How-NOT-to
-> Increase reliability, performance and scalability
5 visitors/day -> 5 million visitors/day
(Don't expect miracle cure !)

Architecture

Our test site

Our base benchmark
Apachebench = useful enough
Result ?

Caching

What is caching ?

What is caching ? select * from article join user on article.user_id = user.id order by created desc limit 10

Caching goals
Source of information (db, file, webservice, …) :
Reduce # of request
Reduce the load
Latency :
Reduce for visitor
Reduce for Webserver load
Network :
Send less data to visitor
Hey, that's frontend !

Theory of caching DB

Theory of caching if ($data == false) DB

Caching techniques
#1 : Store entire pages
Company Websites
Blogs
Full pages that don't change
Render -> Store in cache -> retrieve from cache

Caching techniques
#1 : Store entire pages

Caching techniques
#2 : Store parts of a page
Most common technique
Usually a small block in a page
Best effect : reused on lots of pages

Caching techniques
#2 : Store parts of a page

Caching techniques
#3 : Store SQL queries
↔ SQL query cache
Limited in size

Caching techniques
↔ SQL query cache
Limited in size
Resets on every insert/update/delete
Server and connection overhead
Goal :
not to get rid of DB
free up DB resources for more hits !

Caching techniques

Caching techniques
#4 : Store complex processing results
Not just calculations
CPU intensive tasks :
Config file parsing
XML file parsing
Loading CSV in an array
Save resources -> more resources available

Caching techniques
#4 : Store complex processing results

Caching techniques
#xx : Your call Only limited by your imagination ! When you have data, think :
Creating time ?
Modification frequency ?
Retrieval frequency ?

How to find cacheable data
New projects : start from 'cache everything'
Existing projects :
Look at MySQL slow query log
Make a complete query log (don't forget to turn it off !)
Check page loading times

Caching storage - MySQL query cache
Use it
Don't rely on it
Good if you have :
lots of reads
few different queries
Bad if you have :
lots of insert/update/delete
lots of different queries

Caching storage - Disk
Data with few updates : good
Caching SQL queries : preferably not
DON'T use NFS or other network file systems
especially for sessions
high latency
locking issues !

Caching storage - Disk / ramdisk
Overhead : filesystem access
Limited number of files per directory
-> Subdirectories
Local
5 Webservers -> 5 local caches
-> Hard to scale
How will you keep them synchronized ?
-> Don't say NFS or rsync !

Caching storage - Memcache
Facebook, Twitter, Slashdot, … -> need we say more ?
Distributed memory caching system
Multiple machines ↔ 1 big memory-based hash-table
Key-value storage system
Keys - max. 250bytes
Values - max. 1Mbyte

Caching storage - Memcache
Facebook, Twitter, Slashdot, … -> need we say more ?
Distributed memory caching system
Multiple machines ↔ 1 big memory-based hash-table
Key-value storage system
Keys - max. 250bytes
Values - max. 1Mbyte
Extremely fast... non-blocking, UDP (!)

Memcache - where to install

Memcache - installation & running it
Installation
Distribution package
PECL
Windows : binaries
Running
No config-files
memcached -d -m <mem> -l <ip> -p <port>
ex. : memcached -d -m 2048 -l 127.0.0.1 -p 11211

Caching storage - Memcache - some notes
Not fault-tolerant
It's a cache !
Lose session data
Lose shopping cart data
...

Caching storage - Memcache - some notes
Not fault-tolerant
It's a cache !
Lose session data
Lose shopping cart data
…
Different libraries
Original : libmemcache
New : libmemcached (consistent hashing, UDP, binary protocol, …)
Firewall your Memcache port !

Memcache in code <?php $memcache = new Memcache(); $memcache->addServer( '172.16.0.1' , 11211); $memcache->addServer( '172.16.0.2' , 11211); $myData = $memcache->get( 'myKey' ); if ($myData === false ) { $myData = GetMyDataFromDB(); // Put it in Memcache as 'myKey', without compression, with no expiration $memcache->set( 'myKey' , $myData, false , 0); } echo $myData;

Let's give that a go ! /** * Retrieves the 10 highest rated articles * @return array List of highest rated articles */ static public function getTopRatedArticleList () { if ($articleList = $cache->load( 'topRatedArticleList' ) === false) { $articleList = self :: getTopRatedArticleListUncached (); $cache->save($articleList, 'topRatedArticleList' ); } return $articleList; }

Where's the data ?
Memcache client decides (!)
2 hashing algorithms :
Traditional
Server failure -> all data must be rehashed
Consistent
Server failure -> 1/x of data must be rehashed (x = # of servers)
No replication !

Memcache slabs
(or why Memcache says it's full when it's not)
Multiple slabs of different sizes :
Slab 1 : 400 bytes
Slab 2 : 480 bytes (400 * 1.2)
Slab 3 : 576 bytes (480 * 1.2) (and so on...)
Multiplier (1.2 here) can be configured
Each larger slab has room for fewer items (chunks)
-> Store a lot of very large objects
-> Large slabs might be full
-> Rest of slabs might be free
-> Try to store more -> eviction of data !

Memcache - Is it working ?
Connect to it using telnet
"stats" command ->
Use Cacti or other monitoring tools
STAT pid 2941 STAT uptime 10878 STAT time 1296074240 STAT version 1.4.5 STAT pointer_size 64 STAT rusage_user 20.089945 STAT rusage_system 58.499106 STAT curr_connections 16 STAT total_connections 276950 STAT connection_structures 96 STAT cmd_get 276931 STAT cmd_set 584148 STAT cmd_flush 0 STAT get_hits 211106 STAT get_misses 65825 STAT delete_misses 101 STAT delete_hits 276829 STAT incr_misses 0 STAT incr_hits 0 STAT decr_misses 0 STAT decr_hits 0 STAT cas_misses 0 STAT cas_hits 0 STAT cas_badval 0 STAT auth_cmds 0 STAT auth_errors 0 STAT bytes_read 613193860 STAT bytes_written 553991373 STAT limit_maxbytes 268435456 STAT accepting_conns 1 STAT listen_disabled_num 0 STAT threads 4 STAT conn_yields 0 STAT bytes 20418140 STAT curr_items 65826 STAT total_items 553856 STAT evictions 0 STAT reclaimed 0

Memcache - backing up

Memcache - deleting <?php $memcache = new Memcache(); $memcache->delete( 'myKey' ); $myData = $memcache->get( 'myKey' ); // $myData === false

Memcache - tip
Page with multiple blocks ? -> use Memcached::getMulti() Warning : what if you get some hits and some misses ?

Naming your keys
Key names must be unique
Prefix / namespace your keys !
Only letters, numbers and underscore
md5() is useful
-> BUT : harder to debug
Use clear names
Document your key names !

Updating data

Adding/updating data $memcache->delete( 'ArticleDetails__Toshiba_32C100U_32_Inch' ); $memcache->delete( 'Homepage_Popular_Product_List' );

Adding/updating data

Adding/updating data - Why it crashed

Cache stampeding elePHPants

Cache stampeding

Memcache code ? DB

Cache warmup scripts
Used to fill your cache when it's empty
Run it before starting Webserver !
2 ways :
Visit all URLs
Error-prone
Hard to maintain
Call all cache-updating methods
Make sure you have a warmup script !

Cache stampeding - what about locking ?
Seems like a nice idea, but...
Lock in place
-> lots of new connections
-> memory spike
What if the process that created the lock fails ?

Quick word about expiration
General rule : don't let things expire
Exception to the rule : things that have an end date (calendar items)

So...
DON'T DELETE FROM CACHE (and don't expire unless usefull)

LAMP...
-> LAMMP -> LANMMP

Nginx
Web server
Reverse proxy
Lightweight, fast
7.5% of all Websites

Nginx
No threads, event-driven
Uses epoll / kqueue
Low memory footprint
10000 active connections = normal

Nginx - a true alternative to Apache ?
Not all Apache modules
mod_auth_*
mod_dav*
…
Basic modules are available
Some 3 rd party modules (needs recompilation !)

Nginx - Installation
Packages
Win32 binaries
Build from source (./configure; make; make install)

Nginx - Configuration server { listen 80; server_name www.domain.ext *.domain.ext; index index.html; root /home/domain.ext/www; } server { listen 80; server_name photo.domain.ext; index index.html; root /home/domain.ext/photo; }

Nginx - phase 1
Move Apache to a different port (8080)
Put Nginx at port 80
Nginx serves all statics (images, css, js, …)
Forward dynamic requests to Apache

Nginx for static files only server { listen 80; server_name www.domain.ext; location ~* ^.*.(jpg|jpeg|gif|png|ico|css|zip|tgz|gz|rar|bz2|doc|xls|pdf|ppt|txt|tar|rtf|js)$ { expires 30d; root /home/www.domain.ext; } location / { proxy_pass http://www.domain.ext:8080; proxy_pass_header Set-Cookie; proxy_set_header X-Real-IP $remote_addr; proxy_set_header Host $host; proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for; } }

Nginx - let's give that a go !

Nginx for PHP ?
LANMMP to... LNMPP (ok, this is getting ridiculous)

Nginx with PHP
In the past : spawn-fcgi (from Lighttpd)
Now : PHP-FPM (in PHP 5.3 !)
Runs on port 9000
Nginx connects using fastcgi method
location / { fastcgi_pass 127.0.0.1:9000; fastcgi_index index.php; include fastcgi_params; fastcgi_param SCRIPT_NAME $fastcgi_script_name; fastcgi_param SCRIPT_FILENAME /home/www.phpbenelux.eu/$fastcgi_script_name; fastcgi_param SERVER_NAME $host; fastcgi_intercept_errors on; }

Nginx + PHP-FPM features
Graceful upgrade
Spawn new processes under high load
Chroot
Slow request log !

Nginx + PHP-FPM features
Graceful upgrade
Spawn new processed under high load
Chroot
Slow request log !
fastcgi_finish_request() -> offline processing

Nginx + PHP-FPM - performance ?

Reverse proxy time...

Varnish
Not just a load balancer
Reverse proxy cache / http accelerator / …
Caches (parts of) pages in memory
Careful :
uses threads
Nginx is faster and scales better (but doesn't have VCL)

Varnish - Installation & configuration
Installation
Packages
Source : ./configure && make && make install
Configuration
/etc/default/varnish
/etc/varnish/*.vcl

Varnish - backends + load balancing backend server1 { .host = "192.168.0.10"; } backend server2{ .host = "192.168.0.11"; } director example_director round-robin { { .backend = server1; } { .backend = server2; } }

Varnish - backends + load balancing backend server1 { .host = "192.168.0.10"; .probe = { .url = "/"; .interval = 5s; .timeout = 1 s; .window = 5; .threshold = 3; } }

Varnish - VCL
Varnish Configuration Language
DSL (Domain Specific Language)
-> compiled to C
Hooks into each request
Defines :
Backends (web servers)
ACLs
Load balancing strategy
Can be reloaded while running

Varnish - whatever you want
Real-time statistics (varnishtop, varnishhist, ...)
ESI

Varnish - ESI
Perfect for caching pages
In your article page output : <esi:include src="/latest-news"/>

Varnish with ESI - hold on tight !

Varnish - what can/can't be cached ?
Can :
Static pages
Images, js, css
Pages or parts of pages that don't change often (ESI)
Can't :
POST requests
Requests with Set-Cookie
Very large files (it's not a file server !)
User-specific content

ESI -> no caching on user-specific content ? Logged in as : Wim Godden 5 messages TTL = 5min TTL=1h TTL = 0s ?

Coming to an Nginx near you soon... Logged in as : Wim Godden 5 messages <esim:include src="/news" ttl="5m" /> <esim:include src="/menu" ttl="1h" /> <esim:include src="/top" usercookie="PHPSESS_ID" ttl="1h" />

New message arrives...
Hash using page name and session
Self-chosen key (i.e. 'mails_for_' followed by session)
DB

Advantages
No hits to backend anymore (except the first one) !
Not for user-specific content
Not even for non-specific content

Do we need TTLs ? Logged in as : Wim Godden 5 messages <esim:include src="/news" ttl="5m" /> <esim:include src="/menu" ttl="1h" /> <esim:include src="/top" usercookie="PHPSESS_ID" ttl="1h" />

Advantages
No TTLs for non-specific content
TTL for user-specific content is required (defaults to 5min)
No need to specify ESI parameters in configuration file
Only needs enabling

How many Memcache requests ? Logged in as : Wim Godden 5 messages <esim:include src="/news" ttl="5m" /> <esim:include src="/menu" ttl="1h" /> <esim:include src="/top" usercookie="PHPSESS_ID" ttl="1h" />

Advantages
No TTLs for non-specific content
TTL for user-specific content is required (defaults to 5min)
No need to specify ESI parameters in configuration file
Only needs enabling
Memcache getMulti -> 1 Memcache request per page

Under development
Feature set = unclear
Performance = even more unclear
Debugging code makes it slow
Extends ESI standard, but doesn't follow it entirely
(what standard ?)
Release date ?
End 2011 ?

Tuning

Apache - tuning tips
Disable unused modules -> fixes 10% of performance issues
Set AllowOverride to None
Disable SymLinksIfOwnerMatch
Why ? Site in /var/www/domain.com/subdomain/html
MinSpareServers, MaxSpareServers, StartServers, MaxClients, MPM selection -> a whole session of its own ;-)
Don't mod_proxy -> use Nginx or Varnish !
High load on an SSL-site ? -> put SSL on a reverse proxy

PHP speed - some tips
Upgrade PHP - every minor release has 5-15% speed gain !
Use an opcode cache

Caching storage - Opcode caching

Use an opcode cache
Profile your code
XHProf
Xdebug

KCachegrind is your friend

Use an opcode cache
Profile your code
XHProf
Xdebug
But : turn off profilers on acceptance/production platforms !
Let's see what difference opcode caching and profilers make...

DB speed - some tips
Avoid NOW() -> use PHP date("Y-m-d") as a parameter
Why ? Query cache !
Index, index, index ! (where needed only)
Use same types for joins
i.e. don't join decimal with int
RAND() is evil !
count(*) is evil in InnoDB without a where clause !
(and there are other examples of specific things to avoid)
Select the right storage engine
Persistent connect is not always good !

Caching & Tuning @ frontend http://www.websiteoptimization.com/speed/tweak/average-web-page/

Caching in the browser
HTTP 304 (Not modified)
Expires/Cache-Control header

HTTP 304 First request Next requests

HTTP 304 with ETag First request Next requests

Expires/Cache-control header
Cache-Control
HTTP/1.1
Seconds to expiry
Used by browsers
First request Next requests No requests until item expires
Expires
HTTP/1.0
Date to expire on
Used by old proxies
Requires clock to be accurate !

Pragma: no-cache = evil
"Pragma: no cache" doesn't make it uncacheable
Don't want caching on a page ?
HTTP/1.0 : "Expires : Fri, 30 Oct 1998 00:00:00 GMT" (in the past)
HTTP/1.1 : "Cache-Control: no-store"

Frontend tuning
1. You optimize backend 2. Frontend engineers messes up -> havoc on backend 3. Don't forget : frontend sends requests to backend ! SO...
Care about frontend
Test frontend
Check what requests frontend sends to backend

Tuning frontend
Minimize requests
Combine CSS/JavaScript files
Use inline images in CSS/XHTML (not supported on all browsers yet)

Frontend tuning - inline CSS/XHTML images #navbar span { width: 31px; height: 31px; display: inline; float: left; margin-right: 4px; } .home { background-image: url(data:image/gif;base64,R0lGODlhHwAfAPcAAAAAAIxKAKVjCLW1tb29tcbGvc7OxtZ7ANbWztbW1tbe1t7e1uelMefn1ufn3ufn5+fv3u+MAO/v5+/v7/fGCPf35/f37//nY////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////........MEl0nGVUC6tObNnPceSFBaQVMJAxC4lo3gNOrUaFnTHoAxNm3XVxPfRq139e8BEGAjWD5bgIALw287T8AcAXLly2kjOACdc17higXSIKDO/Lpv7Qq4bw7APgBq8eOzX69InrZ6xe3dbxZffyTGkb8tdx8F+b0Xn2sFsCSBAgTM5lp63RHYnoHUudZgRgkGOGCB+43nGk4OGcQTabKx5dyJKJ7ImoUNCaRRAZYN1ppsrT3Y2gIwyjSQBAtUpABml/0IJGYd6VjQUDH9uBFkGxGm5I8dPQaRUAQUMBdhhBV25ZYUJZBcSAtSJBddWZZ5UAGPOTXlgkNVOSZdBxEwIkYu7VhYnAol5GaadRqF0Uaz0TgXnX2umVFyGakJUUAAADs=); margin-left: 4px; } <img border=0 src="data:image/gif;base64,R0lGODlhHwAfAPcAAAAAAIxKAKVjCLW1tb29tcbGvc7OxtZ7ANbWztbW1tbe1t7e1uelMefn1ufn3ufn5+fv3u+MAO/v5+/v7/fGCPf35/f37//nY/......Uaz0TgXnX2umVFyGakJUUAAADs=">

Tuning frontend
Minimize requests
Use inline images in CSS (not supported on all browsers yet)
Use CSS Sprites

CSS Sprites

Tuning content - CSS sprites

Tuning content - CSS sprites 11 images 11 HTTP requests 24KByte 1 images 1 HTTP requests 14KByte

Tuning frontend
Minimize requests
Use inline images in CSS (not supported on all browsers yet)
Use CSS Sprites (horizontally if possible)
Put CSS at top
Put JavaScript at bottom
Max. no connections
Especially if JavaScript does Ajax (advertising-scripts, …) !
Avoid iFrames
Again : max no. of connections
Don't scale images in HTML
Have a favicon.ico (don't 404 it !)

Tuning frontend
Use GET for Ajax retrieval requests (and cache them !)
Split requests across subdomains
Put statics on a separate subdomain (without cookies !)
www.whatever.com www.whatever.com images.whatever.com

Tuning miscellaneous
Avoid DNS lookups
Frontend : don't use too many subdomains (2 = ideal)
Backend :
Turn off DNS resolution in Apache : HostnameLookups Off
If your app uses external data
Run a local DNS cache (timeout danger !)
Make sure you can trust DNS servers (preferable run your own)
Compress non-binary content (GZIP)
mod_deflate in Apache
HttpGzipModule in Nginx (HttpGzipStaticModule for pre-zipped statics !)
No native support in Varnish

What else can kill your site ?
Redirect loops
Multiple requests
More load on Webserver
More PHP to process
Additional latency for visitor
Try to avoid redirects anyway
-> In ZF : use $this->_forward instead of $this->_redirect
Watch your logs, but equally important...
Watch the logging process ->
Logging = disk I/O -> can kill your site !
Slashdot effect

Above all else... be prepared !
Have a monitoring system
Use a cache abstraction layer (disk -> Memcache)
Don't install for the worst -> prepare for the worst
Have a test-setup
Have fallbacks
Turn off non-critical functionality

Questions ?

Contact
Twitter @wimgtr
Web http://techblog.wimgodden.be
Slides http://www.slideshare.net/wimg
E-mail [email_address]

Please...
Rate my talk : http://tinyurl.com/cachetune
Vote to see me talk at Confoo : http://www.confoo.ca
Caching and tuning fun for high scalability
Keeping old code alive without non-stop hassle
Beyond PHP : it's not (just) about the code !
Who's in control of your PHP app ?
Creating Fast, Dynamic ACLs in Zend Framework

Thanks !

Caching and tuning fun for high scalability @ FrOSCon 2011

by Wim Godden on Aug 23, 2011

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Caching and tuning fun for high scalability @ FrOSCon 2011 Presentation Transcript

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