Analysis and Performance

Information Systems 337

Prof. Harry Plantinga

Analysis

Your boss says "Who's visiting our site? Where are they coming from? What pages are popular? What paths are users taking through the site? What are the problem pages where we lose visitors?"

Analysis options: Read the raw logfile Set up a logfile analysis program Sign up for Google Analytics

Google Analytics

An amazing tool… Where do my customers live? What path do they take through the site? What links are popular? Would a certain change improve the site?

(A/B testing)

How to add Google Analytics to a web site? Sign up for GA, install the google_analytics

module

Suppose…

You set up a new web site using Drupal

Performance is mediocre What was a site in the top 5% (for speed) drops

near the bottom… 5 seconds for a page load 0.75sec minimum for every file served high server load averages occasionally, load average shoots up and server

crashes

What to do?

Minimize download time

Reduce the number of hits (stylesheets, images) per pageview Use Drupal's CSS and JS optimization (although

they didn't exist in Drupal 4…)[ Reduced from >30 to about 20 files per pageview

(stylesheets, artwork, etc) this way] Can also minimize javascript

Limit 2 files at once per server Any way to improve this?

Second domain name

Add a second server on a different domain name Serve static files (artwork, stylesheets, etc)

from a separate server Allow 4 files to be downloaded at once between

the two domain names Can turn on maximum caching for static files

Caching

Turn on Drupal's page cache

Make sure users' browser cache works as well as possible Static content should never expire Change filename for revised files Static server: add an Expires or Cache-control

header: make sure content doesn't expire

Still, 40-60% of visitors come with an empty cache…

Optimize artwork

Make sure artwork files are small optimize in Photoshop or another program

Many small files == slow. How to reduce? combine artwork into one background image use jQuery to round corners use CSS Sprites use inline images in stylesheets with data: urls

Reduce download times

80-90% of wait time is downloading content

More ideas Compress components

Accept-Encoding: gzip, deflate? Then deflate! Apache: use mod_deflate

Use a content delivery network E.g. Akami Can improve av. response time 20% or more

Make pages appear faster

Stylesheets at the top, so pages can be rendered right away

Scripts at the bottom

Specify image dimensions

Minimize expensive page components

Page Speed

Google Page Speed tools help identify ways to improve performance Firebug add-on for Firefox Apache module mod_pagespeed

Problems remain?

At this point we still had very slow page display times and occasional load average spike/crash

How to debug?

What are the possible server performance bottlenecks?

Server Bottlenecks

Possible server bottlenecks Is the CPU maxed out? Running out of RAM Disk speed, transactions per second Network bandwidth Database capacity

How to test?

Disk maxed out?

Check disk activity (reads vs. writes) vmstat on linux performance monitor on windows or write your own…

If pegged, find cause excessively verbose logging? background process, e.g. backups? poorly configured database? too many database writes? some other bad algorithm?

Running out of bandwidth?

Get a bigger pipe

Or, send less data smaller artwork better caching gzip compression

Running out of RAM?

Check with linux top or free, performance monitor, etc.

Each server process takes 20-100 MB or more

Each Apache or Drupal module takes more

Our crashes were due to running out of RAM, then swap space

Solutions? Set MaxClients appropriately Turn down Keepalive time! (Default 15, to 2?) MaxRequestsPerChild to lower number, e.g. 300 Get more RAM

Running out of CPU?

Check with top (linux/mac) or performance monitor (windows)

PHP is interpreted

Each request: load, compile all the code… This was taking us something like 0.5 secs of CPU

time per page

Use a PHP Accelerator (bytecode cache) e.g. eAccelerator, Zend, Alternative PHP Cache

Application profiling

Get a faster CPU

Database swamped?

Use mysqladmin to figure out how many transactions per second you are using

How many transactions per second can a database process? fully cached: lots requiring a disk access: 100? 200?

Solutions: optimize expensive queries add indexes on tables enlarge server's query cache / tune server reduce database writes

Drupal-specific optimizations

Some improvements you can make in Drupal: Turn on page caching Stylesheet optimization Prune the sessions table/make sessions shorter

Reduce time before garbage collection (cron) Prune error reporting logs (watchdog table) Automatic throttling

What next?

I've done all that. What else can I do? Separate database server Load balancer and additional servers Database replication