1.
Caching Strategies Michal Špaček, Skype; WebExpo 2011 , Prague @spazef0rze, www.michalspacek.cz

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What the... Cache ? HDD cache, CPU cache, DNS cache, web cache, geocache

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What the... Cache ? HDD cache, CPU cache, DNS cache, web cache , geocache

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CLIENT (BROWSER) WEB SERVER DATABASE SERVER

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HTTP level caching

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Client local disk/memory cache CLIENT (BROWSER) WEB SERVER

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Response headers: Expires Last-Modified ETag Cache-Control Pragma CLIENT (BROWSER) WEB SERVER

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Expires: HTTP-date Expires: Sat, 24 Sep 2011 12:00:00 GMT < Expires CLIENT (BROWSER)

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Expires: HTTP-date Expires: Sat, 24 Sep 2011 12:00:00 GMT > Expires CLIENT (BROWSER) WEB SERVER

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Last-Modified: HTTP-date Following request: If-Modified-Since: HTTP-date

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Last-Modified: HTTP-date Following request: If-Modified-Since: HTTP-date Response: Entity modified: HTTP 200 OK Not modified: HTTP 304 Not Modified

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Last-Modified: HTTP-date Saves bandwidth!

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ETag: quoted-string Following request: If-None-Match: quoted-string

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ETag: quoted-string Following request: If-None-Match: quoted-string Response: No match : HTTP 200 OK A match: HTTP 304 Not Modified

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Saves bandwidth, too! ETag: quoted-string

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If-Modified-Since If-Unmodified-Since If-None-Match If-Match

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ETag × Last-Modified hash (GUID) × HTTP-date (seconds)

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ETag × Last-Modified hash (GUID) × HTTP-date (seconds) weak+strong validation × strong

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ETag × Last-Modified hash (GUID) × HTTP-date (seconds) weak+strong validation × strong needs content × needs date

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Request+Response header Cache-Control: whatever

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Request+Response header whatever = max-age , no-cache , public , must-revalidate (response only), ... Cache-Control: whatever

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Pragma: no-cache Request+Response header

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Pragma: no-cache Request+Response header Request: HTTP 1.0 variant of Cache-Control: no-cache

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Pragma: no-cache Request+Response header Request: HTTP 1.0 variant of Cache-Control: no-cache Response: meaning undefined, wtf

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Proxy cache CLIENT (BROWSER) WEB SERVER

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Proxy cache CLIENT (BROWSER) WEB SERVER

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Application level caching

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Configuration Does not change often

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Configuration Does not change often Parse (files)/read (from db) and store to APC

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APC: The Alternative PHP Cache PHP extension Data store (also opcode cache)

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APC: The Alternative PHP Cache Data persist between requests

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APC: The Alternative PHP Cache Data persist between requests … until deleted or cache cleared or server restarted

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Database connection cache Persistent connections (don't work) Connection pooler

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Database query cache Some systems have query cache

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Database query cache Some systems have query cache Some don't

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Result set cache Some data don't change

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Result set cache Some data don't change Fetch and store to memcached

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Memcached Client-server architecture Key-value in memory store for strings and objects

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Problems with caching

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Data change sometimes but not often enough Employee list of a company

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Data change sometimes but not often enough Employee list of a company Invalidate cache when adding or removing employees

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Data change sometimes and delay is okay Translations from database

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Data change sometimes and delay is okay Translations from database Introduce cache lifetime

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Moar cache keys for the same data Sorted employee list (asc, desc)

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Moar cache keys for the same data Sorted employee list (asc, desc) Cache groups

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Cache groups Keys: list-sorted-asc, list-sorted-desc

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Cache groups Keys: list-sorted-asc, list-sorted-desc Group „list“: list-sorted-asc, list-sorted-desc, list-unsorted

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Cache groups Keys: list-sorted-asc, list-sorted-desc Group „list“: list-sorted-asc, list-sorted-desc, list-unsorted Delete group „list“ when adding/removing

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Cache wherever and whatever

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… but delete your whatever when needed

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Caching is magic

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Caching is magic but not automagic

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Caching is magic but not automagic until now

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www.phpguru.cz/kaskadova-cache <ul>2010 © Skype – As seen on TV </ul><ul>Slide </ul>

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Practical implementation, anyone ? <ul>2010 © Skype – As seen on TV </ul><ul>Slide </ul>

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<ul>Thanks for listening Michal Špaček, @spazef0rze BTW, love caching? skypecareers.com! </ul>