[HBASE-8001] Avoid unnecessary lazy seek

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 0.94.5
• Fix Version/s: 0.98.0, 0.95.2
• Component/s: regionserver
• Hadoop Flags: Reviewed
• Assignee: Raymond Liu
• Reporter: Raymond Liu
• Created: 05/Mar/13 08:30
• Updated: 23/Sep/13 19:22
• Resolved: 19/Jun/13 05:01

Description

Lazy seek helps to reduce the real seek needed for multi hfile, when the kv from newer hfile is enough to satisfy the query.

While in many case, it just push the real seek later, and do not reduce the number of real seek. e.g. there are only one hfile, or storefilescanner is closed and only one left, or the scan need to go through all the versions, or there are only one version of row and a sequence scan is performed. In these case, lazy seek just bring extra overhead.

Issue Links

• depends upon: HBASE-8012 Reseek should position to the beginning of file for the first time it is invoked with a KV smaller than the first KV in file
• is related to: HBASE-4433 avoid extra next (potentially a seek) if done with column/row
• is related to: HBASE-4465 Lazy-seek optimization for StoreFile scanners