Ric GoellMing LeiWeb CacheOracle Corporation

Web Caching for Database CentricApplications

Outline• Part I - Introduction to Web Caching• Part II - Designing with Caching in Mind

– A process for analyzing the potential for caching benefits

• Part III – Partial Page Caching with ESI– Edge Side Includes (ESI) – a standards based

technology for page and fragment caching– JESI – A set of JSP tags that support ESI

Part I Why Web Caching?

• Content is becoming more dynamic for a richer and more personal Web experience.

• The number of people using web based applications is growing beyond the limits of traditional infrastructures.

• User expectations are growing – they expect more relevant content and fast response times

• Large “Farms” are costly to purchase and manage

Caching on the Web

Browser Cache

ForwardProxy

Internet/Intranet

Edge Servers

ReverseProxy

ApplicationServer

Database

Central Data CenterCDN/eCDN

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E-Commerce PerformanceMeasuring response time isn't enough

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Throughput in pages/sec

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Webcache

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Cache Hit Rate

• Cache hits are practically freefree when compared to generating dynamic pages.

• Focus is on improving cache hit rates. 0

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Throughput (Requests per second)

Web Cache EJB

Why don’t more apps provide caching

• “But my pages have too much customization to be cacheable.”

• A lame excuse – new tools allow customized and dynamic content to be cached– Page fragments can be assembled– Request and Response Variables can be included– Cache Consistency tools to help with invalidation

Part II: Designing with Caching in Mind

• A 3 Step Process– Page Analysis – Determining what to cache– Disambiguation – Key Generation– Cache Consistency – Removing items from

cache

Page AnalysisWhen designing a page layout, define fragments with

similar cache policies – early in design process• When evaluating the benefit of caching pages or

fragments, each of the following should be considered:– Share-ability – How many users share this content?– Generation Cost – How computationally intensive is

the generation of this content?– Frequency – How many times will this content be

viewed (even within one user’s session) before it changes?

• Note that even user specific content may be desirable to cache if it accessed frequently

Disambiguation – Cache Key Definition

Differentiating documents based on specific requests.• URLs• Post Body• HTTP Headers

– Cookies

• MVC Apps tend to have less information in the request. Heavy use of backend state can reduce Web Cache benefits.

Consistency Management

• Expiration – Time Based

• Invalidation based – explicit message to cache servers to remove content from cache

• Validation Based– ETAG and GIMS (similar capabilities for

fragments)

• Don’t be unnecessarily restrictive

Session State Management

• Web Sites often use session keys to track user state and identify data on the server side.

• Web Cache was designed to work with sessions by transparently allowing session establishment and updates.

• Additionally it was designed to allow for caching of documents that include sessions.

Session Encoded URLs

Session Ahttp://store.oracle.com/cec/cstage?session_ID=33436

Session Bhttp://store.oracle.com/cec/cstage?session_ID=33437

Part III PartialPage Caching & Content Assembly

• Edge Side Includes (ESI) – an XML-like markup language used to define

cacheable and non-cacheable content fragments

– a content invalidation protocol for cache consistency

• Edge Side Includes for Java (JESI)– a custom tag library to facilitate the use of ESI with

JSP applications

Industry Support for ESIAn open specification.

ESI published as a W3C Note.

JESI submitted to JCP as JSR 128.

See www.esi.org for more info.

Summary of JESI Tags

TagTag PurposePurpose

<jesi:include><jesi:include>

<jesi:control><jesi:control>

<jesi:template><jesi:template>

<jesi:fragment><jesi:fragment>

<jesi:codeblock><jesi:codeblock>

<jesi:personalize><jesi:personalize>

<jesi:invalidate><jesi:invalidate>

Used in a “template” page to indicate to the ESI processor how to assembe the fragments (the tag generates the <esi:include> tag.

Assign an attribute (e.g., expiration) to templates and fragments.

Used to contain the entire content of a JSP container page within its body.

Specify that a particular piece of code needs to be executed before any other fragment is executed.

Encapsulate individual content fragments within a JSP page.

Explicitly remove and/or expire selected objects cached in an ESI processor.

Insert personalized content into a page where the content is placed in cookies and inserted into the page by the ESI processor.

JESI Personalization

The URL query string has the Personal Valuehttp://Machine:port/zyz?user_name=JaneJane

<HTML>Welcome to the Oracle Store

<jes:personalize name=”user_name”>

...</HTML>

What is ESI?

Why ESI?

• ESI is in production– Co-developed with Akamai and Oracle– IBM is also implementing ESI

• ESI is an open language– Maturing through real usage– W3c note

ESI at a glance

• Templates and Fragments– include & inline

• Variables– Query String Variables– Cookie Variables– Environment Variables

• A good sample App:– http://otn.oracle.com/sample_code/products/ias/web_cache/htdocs/jesi/Readme.html

ESI Personalization

The URL query string has the Personal Valuehttp://Machine:port/zyz?user_name=JaneJane

<HTML>Welcome to the Oracle Store<esi:vars> <esi:vars>

$(QUERY_STRING{'user_name'})! $(QUERY_STRING{'user_name'})!

</esi:vars></esi:vars>

...</HTML>

<esi:include> Model

<html>...<esi:include

src=”/news101”>...</html>

/sample.html (template)

<table>...</table>

/news101

/sample.html

Cache Storage

Page Assembly

Cache Response

Template/news101

<esi:environment>

...<esi:environment src=/stocks.xml

name=stock/>

...<esi:vars>ORCL $(stock{orcl_p}) $(stock{orcl_c}) YHOO $(stock{yhoo_p}) $(stock{yhoo_c}) </esi:vars>

...

/sample.html

/sample.html

Cache Storage

Page Assembly

Cache Response

Template/stocks.xml

<orcl_p>8.94</orcl_p><orcl_c>+0.09</orcl_c><yhoo_p>16.55</yhoo_p><yhoo_c>-0.46</yhoo_c>

/stocks.xml

ESI - Storage & Assembly• Parsing is only done

the first time a page is fetched.

• A buffer array is generated for a scatter/gather network write

• This buffer is maintained in the cache for fast cache hits without page assembly processing

Template 1

Fragment 1

Fragment 2

Fragment 3

BufferArray

ESI PerformanceThroughput

(Requests per second)

971

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Web Cache Portal App

• This test measured a real portal application without Web Cache and ESI.

• Either the Portal App or Web Cache did the page assembly

• 10 portlets

Other Interesting Web Cache Features / Topics

• Invalidation / Consistency Management– Expiration based– Invalidation based

• Clustering

• Cache Hierarchies