An Introduction To Heritrix Gordon Mohr Chief Technologist, Web Projects Internet Archive

Web Collection Since 1996 Over 4x1010 resources (URI+time) Over 400TB (compressed)

Web Collection: via Alexa Alexa Internet Private company Crawling for IA since 1996 2-month rolling snapshots Recent: 3 billion URIs, 35 million websites, 20 TB Crawling software Sophisticated Weighted towards popular sites Proprietary: we only receive the data

Heritrix: Motivations #1 Deeper, specialized, in-house crawling Sites of topical interest Contractual crawls for libraries and governments US Library of Congress Elections, current events, government websites UK Public Records Office, US National Archives Government websites Using our own software & machines

Heritrix: Motivations #2 Open source Encourage collaboration on features and best practices Avoid duplication of work, incompatibilities Archival-quality Perfect copies Keep up with changing web Meet evolving needs of Internet Archive and International Internet Preservation Consortium

Heritrix New Open-source Extensible Web-scale Archival-quality Web crawling software

Heritrix: Use Cases Broad Crawling Focused Crawling Large, as-much-as-possible Focused Crawling Collect specific sites/topics deeply Continuous Crawling Revisit changed sites Experimental Crawling Novel approaches

Heritrix: Project Heritrix means heiress Java, modular Project website: http://crawler.archive.org News, downloads, documentation Sourceforge: open source hosting site Source-code control (CVS) Issue databases “Lesser” GPL license Outside contributions

http://crawler.archive.org

Heritrix: Milestones Summer 2003: Prototypes created and tested against existing crawlers; requirements collected from IA and IIPC October 2003-April 2004: Nordic Web Archive programmers join project, add capabilities January 2004: First public beta (0.2.0) Used for all in-house crawling since February & June 2004: Workshops for Heritrix users at national libraries August 2004: Version 1.0.0 released

Heritrix: Architecture Basic loop: 1. Choose a URI from among all those scheduled 2. Fetch that URI 3. Analyze or archive the results 4. Select discovered URIs of interest, and add to those scheduled 5. Note that the URI is done and repeat Parallelized across threads (and eventually, machines)

Key components of Heritrix Scope which URIs should be included (seeds + rules) Frontier which URIs are done, or waiting to be done (queues and lists/maps) Processor chains configurable sequential tasks to do to each URI (code modules + configuration)

Heritrix: Architecture

Heritrix: Processor Chains Prefetch Ensure conditions are met Fetch Network activity (HTTP, DNS, FTP, etc.) Extract Analyze – especially for new URIs Write Save archival copy to disk Postprocess Feed URIs back to Frontier, update crawler state

Heritrix: Features & Limitations Other key features: Web UI console to control & monitor crawl Very configurable inclusion, exclusion, politeness policies Limitations: Requires sophisticated operator Large crawls hit single-machine limits No capacity for automatic revisit of changed material Generally: Good for focused & experimental crawling use cases; not yet for broad and continuous

Heritrix console

Heritrix settings

Heritrix logs

Heritrix reports

Heritrix: Current Uses Weekly, Monthly, 6-monthly, and special one-time crawls Hundreds to thousands of specific target sites Over 20 million collected URIs per crawl Crawls run for 1-2 weeks

Heritrix: Performance Not yet stressed, optimized Current crawls limited by material to crawl and chosen politeness, not our performance Typical observed rates (actual focused crawls) 20-40 URIs/sec (peaking over 60) 2-3Mbps (peaking over 20Mbps) Limits imposed by memory usage Over 10,000 hosts/over 10 million URIs (512MB machine, more on larger machines)

Heritrix: Future Plans Larger scale crawl capacity Giant focused crawls Broad whole-web crawls New protocols & formats Automate expert operator tasks Continuous and dynamic crawling Revisit sites as they change Dynamically rank sites and URIs

Latest Developments 1.2 Release (next week) 1.4 Release (January 2004) Configurable canonicalization Handles common session-IDs, URI variations Politeness by IP address Experimental more memory-efficient Frontier Bug fixes 1.4 Release (January 2004) Memory robustness Experimental multi-machine distribution support

The End Questions?