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Web Caching

Web Caching. By Neeraj Agrawal. Caching. Caching is widely used for improving performance in many context( e.g processor caches in hardware, buffer pool in DBMS etc). Where and what to cache in web context? Many points and many kind of objects! Focus is on Transactional/Database apps.

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Web Caching

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  1. Web Caching By Neeraj Agrawal

  2. Caching • Caching is widely used for improving performance in many context( e.g processor caches in hardware, buffer pool in DBMS etc). • Where and what to cache in web context? • Many points and many kind of objects! • Focus is on Transactional/Database apps.

  3. What Where When and How Considerations for caching in web context are: • What, when and where to cache • Granularity of caching: web pages, fragments of pages, servlet execution result, SQL query results etc • Location of cache: client, proxy, edge of the net, internet service provider (ISP), edge of enterprise, application server (EJBs etc), web server, database server.

  4. What Where When and How • Caching and Invalidating policies: Pull vs Push, freshness maintenance, triggers. • Related DB Technologies: • Replication • Materialized views • Mediator systems • Buffer management.

  5. Common Points of Caching • Browser • Proxy (Forward proxy cache) • Enterprise/ISP Edge Servers • Web Server • Application Server • Databases

  6. Front End Cache Caches data + markup Cache can be app independent Static pages easily cached Cache Models • Data Cache • Cache Data • Effectiveness depends on app design

  7. Cache Models • Distributed Applications • Multiple copies distributed around net • Turns caching into content management problem.

  8. HTTP Caching Today • Multiple cache between browser and server • HTTP header control • Whether a page can be cached • Cache expiration time. • Full pages and images can be cached. • Unable to cache html fragments

  9. Dynamically Generated Pages • Increased due to • Database centric e-commerce application • Frequently update contents • Personalization • Proxy caching is ineffective for such pages

  10. Caching Data-intensive Web Sites • Relies on the declarative spec of web sites • Data content is extracted from DBMS • Website structure and content is separate from graphical representation XSLT. • The mapping between raw data and logical model of web is described by declarative language (WeaveL) • HTML page is generated from XML and XSLT

  11. Materialization Strategies • What kind of data must be materialized? • When must materialization must be performed? • Where should the materialized intermediate result must be placed for effective performance improvements? • How are updates are propagated to the materialized data? • Which particular data must be materialized and which must be computed upon request?

  12. Approaches • Materialization (HTML) • Good response time • High space overhead • Propagating update to materialization difficult • Not always possible (forms) • Materialization granularity is not always appropriate

  13. Approaches • Cache DBMS query results • Significant performance improvement • Simple update propagation • Granularity • Cache intermediate XML • Complex update propagation • Granularity • Eliminate cost of database connection

  14. WeaveL

  15. XML Fragment

  16. Weave Web Site Management System

  17. Runtime Policies

  18. Conclusion • Results • Better performance with mixed caching

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