Caching For Cash
Dutch PHP Conference Amsterdam, June 2009
Pareto Principle
80 / 20 Rule
80 / 20 Rule
20% of sales people produce 80% of sales
80 / 20 Rule
20% of the population receives 80% of the income
80 / 20 Rule
20% of the causes produce 80% of the effects
The golden rule80% of response time is spent downloading
content
PerceptionTrick the end user intothinking your site is fast!The
users perception is more relevant than actual unload-to-onload
response time.
Definition of "user onload" is undefined or varies from one web
page to the next.
It all depends on how we look at things, and not how they are in
themselves.
- Carl G. Jung
Perception40 60% of all users arrivewith an empty cacheUser
needs to download all components
Coming for the first time
Force refresh of the site
Browser automagically cleared the cache based on settings
Perception
User needs to download all components
Coming for the first time
Force refresh of the site
Browser automagically cleared the cache based on settings
Key factor in performanceFewer HTTP RequestsEasy to improve
on
HTTP Requests
Cookies
Sent with static contentSlow upstream speedBig cookies
Cookie SizeResponse Time (Delta)
0 bytes78 ms ( 0 ms)
500 bytes79 ms ( +1 ms)
1000 bytes94 ms (+16 ms)
1500 bytes109 ms (+31 ms)
2000 bytes125 ms (+47 ms)
2500 bytes141 ms (+63 ms)
3000 bytes156 ms (+78 ms)
Times are for page loads on DSL (~800 kbps).
Experimenting time!Yahoo ran the experiment.Ran against an empty
page
Eliminate unnecessary cookiesKeep sizes lowAppropriate domain
levelsSet Expires date appropriately
Cookies
Be aware of max connection limits in browsersCNAME to point
multiple sub domains to the same IP
Maximize Parallel DownloadsOlder IE: 6 overall, 2 per host
Older FF had 24 as overall and 8 per host
Newer FF: 30 overall, 15 per host
One domain = 2 Parallel connections
Maximize Parallel Downloads
Two domains = 4 Parallel connections
Maximize Parallel Downloads
Too many hostnames can cause complications
2 4 sub domains is a good average
Maximize Parallel DownloadsMany host names = more DNS lookups,
adds delay
Consider the effects of CPU thrashing for the client
Lookup times vary across ISPs and geographic locations
Combining 6 scripts into 1 eliminates 5 requests
Challenges: develop as separate modules
combinations vs. loading more than needed
Combine filesdynamically combine and cache
Combine and minimize before a release
JavascriptJS does not comply with the parallel downloading
rule
script defer attribute is not a solutionblocks rendering and
downloads in FF
slight blocking in IE
Solution: move them as low in the page as possible
Javascript
Javascript MinificationCrushes the filesStrips out all
cruftVoodoo magic
Javascript MinificationJSMinDojo ShrinksafePackerYUI
Compressor
http://short.ie/compression-rates
You can affect users download times
GzipGzip can be used on
JS
CSS
XML
JSON
GzipGzip should not be used on
Images
PDFs
Compressed data formats
404robots.txtfavicon
CSS Sprites
ImagesDon't use HTMTL attributes to scale
Favicon keep it around, keep it small
ImagesBadly optimizedThumbnailsPNG can be compacted 50%, no
quality lossOptiPNG
Tread the users' pathTest on slow connections
Slow proxies for developers
Content Delivery NetworkData served through a single domainSmart
routing softwareData closer to the end user Less latency
Content Delivery Network
Amazon CloudFront
Expires HeadersAppropriate datesCache far in the futureChange
file names on releases
ETagsHash tag to compare between browser and serverGives more
flexibility than last-modified-dateGreat on a single server
setup
Hash like tag to compare browser cache against the server
version
Only download if hash has changed
Gives more flexibility than last-modified date
Great on a single server setup
ProblemsTypically unique to a serverDisable if not being
used!
Typically unique to a server
Default behavior in Apache and IIS
If hash don't match between server, then browser cache is not
used
Proper Expires Headers won't help
Remove ETags if not being used to its fullest
FarmsUse options that are not unique per server
Firefox ExtensionsFirebugFirecookieYslowPage SpeedHammerhead
http://stevesouders.com/hammerhead/
http://code.google.com/speed/page-speed
Knowledge rests not upon truth alone, but upon error also.
- Carl G. Jung
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