[HBASE-2000] Coprocessors

• Type: New Feature
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 0.92.0
• Component/s: Coprocessors
• Hadoop Flags: Reviewed
• Assignee: Unassigned
• Reporter: Andrew Kyle Purtell
• Created: 21/Nov/09 16:49
• Updated: 20/Nov/15 13:01
• Resolved: 11/Jun/11 14:12

Description

From Google's Jeff Dean, in a keynote to LADIS 2009 (http://www.scribd.com/doc/21631448/Dean-Keynote-Ladis2009, slides 66 - 67):

BigTable Coprocessors (New Since OSDI'06)

• Arbitrary code that runs run next to each tablet in table
  • As tablets split and move, coprocessor code automatically splits/moves too

• High-level call interface for clients
  • Unlike RPC, calls addressed to rows or ranges of rows

• coprocessor client library resolves to actual locations
  • Calls across multiple rows automatically split into multiple parallelized RPCs

• Very flexible model for building distributed services
  • Automatic scaling, load balancing, request routing for apps

Example Coprocessor Uses

• Scalable metadata management for Colossus (next gen GFS-like file system)

• Distributed language model serving for machine translation system

• Distributed query processing for full-text indexing support

• Regular expression search support for code repository

For HBase, adding a coprocessor framework will allow for pluggable incremental addition of functionality. No more need to subclass the regionserver interface and implementation classes and set hbase.regionserver.class and hbase.regionserver.impl in hbase-site.xml. That mechanism allows for extension but at the exclusion of all others.

Also in HBASE-2001 currently there is a in-process map reduce framework for the regionservers. Coprocessors can optionally implement a 'MapReduce' interface which clients will be able to invoke concurrently on all regions of the table. Note this is not MapReduce on the table; this is MapReduce on each region, concurrently. One can implement MapReduce in a manner very similar to Hadoop's MR framework, or use shared variables to avoid the overhead of generating (and processing) a lot of intermediates. An initial application of this could be support for rapid calculation of aggregates over data stored in HBase.

Issue Links

• is blocked by: HBASE-2321 Support RPC interface changes at runtime
• relates to: HBASE-1845 MultiGet, MultiDelete, and MultiPut - batched to the appropriate region servers
• relates to: HBASE-1935 Scan in parallel
• relates to: HBASE-2893 Table metacolumns
• relates to: HBASE-3340 Eventually Consistent Secondary Indexing via Coprocessors
• relates to: HBASE-3341 Increment Row-Level Group Commit via Coprocessors
• relates to: HBASE-3342 Server-side Row-level Inverted Index Join via Coprocessors
• relates to: HBASE-74 [performance] When a get or scan request spans multiple columns, execute the reads in parallel

Sub-Tasks

• Coprocessors: Client side support: Closed
• Coprocessors: Colocate user code with regions: Closed
• Allow Observers to completely override base function: Closed
• Coprocessors: Lifecycle management: Closed
• Coprocessors: Coprocessor host and observer for HMaster: Closed
• Coprocessors: Extend server side integration API to include HLog operations: Closed
• Coprocessors: Distributed query processing: Closed
• Coprocessors: Support aggregate functions: Closed
• Coprocessors: Support small query language as filter on server side: Closed