How to optimise a web server to reduce latency and bandwidth to viewers

1. Website Optimisation
CLUG March 2012

2. contents
Network
Compression
HTTP Caching
Structuring
Measurement
Application Caching
Monitoring

3. contents
Client
Network
Compression
HTTP Caching
Structuring
Measurement
Application Caching
Database tuning
Monitoring Server

4. Network
mtr ­c 10 ­r www.openquery.com
HOST: spaceman.localhost
Loss% Snt Last Avg Best
Wrst StDev
1.|­­ 192.168.1.1
0.0% 10 0.8 2.6 0.7 19.3
5.8
2.|­­ 192.168.3.254
0.0% 10 1.1 1.2 1.1 1.5
0.1

5. Network (DNS)
Check whois is showing the right nameserver
whois openquery.com
NS1.LINODE.COM
NS2.LINODE.COM
NS3.LINODE.COM
NS4.LINODE.COM
NS1.CREATIVECONTINGENCIES.COM
NS2.CREATIVECONTINGENCIES.COM
NS3.CREATIVECONTINGENCIES.COM
Ensure correct record is returned by querying
each nameserver
dig www.openquery.com @ns1.creativecontingencies.com

6. Network (SSL/TLS)

7. Network (SSL/TLS)
Session Tickets - 8 packets 3 roundtrips before application data
EDH crypto – computational expensive by has perfect forwards secrecy

8. Network (HTTP keep-alive)
Request / Response header
Connection:keep-alive
On by default. Can't handle variable length pages

9. Compression
Gzip/deflate

10. Compression
Apache's HTTPd
Enable mod_deflate
<IfModule mod_deflate.c>
SetOutputFilter DEFLATE
</IfModule>
Lighty
Enable “mod_compress” in server.modules
Nginx
gzip on;

11. Compression
PHP
Php.ini zlib.output_compression On

12. HTTP Caching
RFC 2616 Hypertext Transfer Protocol –
HTTP/1.1

13. HTTP Caching
Etag
Unique string – usual some form of digest
Browsers request with HTTP header:
If-None-Match: “uniquestring....”
Server response: 304 not modified if nothing
changes

14. HTTP Caching (Etag)
HTTPd
FileETag Mtime

15. HTTP Caching (Expires)
HTTP Response header
Expires: Thu, 01 Dec 2012 16:00:00 GMT
Date:Thu, 22 Mar 2012 01:00:17 GMT
Last-Modified:Sun, 11 Mar 2012 20:55:16 GMT
HTTP Request
If-Modified-Since: Sat, 29 Oct 1994 19:43:31
GMT

16. HTTP Caching (Cache-Control)
Cache-Control = "Cache-Control" ":"
1#cache-directive
cache-directive = cache-request-directive
| cache-response-directive
cache-request-directive =
"no-cache" ; Section
14.9.1

17. Gzip + Caching
Savings
On initial response: 104.2K (vs 255.6K) / 44
trunk/roundcubemail/.htaccess ¶ requests)
<IfModule mod_deflate.c>next page: 6.2K 2 requests (vs 204.7K / 44
On
requests)
SetOutputFilter DEFLATE
</IfModule>
<IfModule mod_headers.c>
# replace 'append' with 'merge' for Apache
version 2.2.9 and later
Header append Cache-Control public env=!

18. Use Yslow / Firebug
Structuring

19. Measurement

20. Measurement (Application)
create table `timings` ( `id` int(4) NOT NULL
AUTO_INCREMENT, 'host' varchar(20),'page'
varchar(120), int t1,int t2, int t3.....)
And in the index.php
$sample = rand(0,100) < 5; # 5% sample rate
if ($sample) $t0 = microtime(TRUE);

21. Application Caching
Be strategic – cost / benefit
Hard to generate – graphs, database queries,
complex maths
Frequent pages: front pages, rss, ajax

22. Application Caching (duplicate)
if (!$db->count('name', $name,
DB_CACHE))
{
// if no cache entry exists, fetch the
appropriate html and insert
...
} else {
// row exists - determine if it is still valid

23. Application Caching
Cache an entire page
Memcache is your friend – RAM, autoexpire,
overload intelligent expire
Share between servers
Nice API in all languages
e.g. PHP
public mixed Memcached::get ( string $key [, callable
$cache_cb [, float &$cas_token ]] )

24. Application scaling
If the application scales by adding webservers
you will save on hosting on high power servers
Ensure application is stateless
Reverse proxy state-full bits to central server if
needed
CDNs or separated servers for static content
saves lots of cpu (latency, keep alives)

25. Application APC
Graph from apc.php as part of the php_apc package

26. Database
Know what indexes are and which queries aren't
using them.
EXPLAIN {sql expression} (Postgresql and Mysql)
EXPLAIN ANALYSE {sql expression}
Slow query log – enable
Know differences between MySQL engines
Tune your server
Defaults well out of proportion with your sever.

27. Database (continued)
Searching text in SQL – Use Sphinxsearch
instead
Same sql interfaces, pulls off database – much
quicker at full text search

28. Databases (application)
Eventually one DB will be too little
Plan to buy big hardware (Oracle) or plan to use
a replicated database (for reads)
Some reads will need to occur on the master.
The ones where the data was likely just
changed very recently

29. Monitoring

30. Monitoring
Include resource usage
Cpu / RAM / processes / forking / swap / IO /
Bandwidth...
Web server – pages/second, threads
Database – query cache hits/misses,
connections, replication delay
Business value: page load time.
Alert if boundaries exceeded