[HBASE-15648] Reduce number of concurrent region location lookups when MetaCache entry is cleared

• Type: Sub-task
• Status: Resolved
• Priority: Major
• Resolution: Later
• Affects Version/s: 1.2.0, 1.3.0
• Component/s: Client
• Assignee: Mikhail Antonov
• Reporter: Mikhail Antonov
• Created: 13/Apr/16 22:31
• Updated: 06/Mar/20 23:49
• Resolved: 18/Jan/20 00:04

Description

It seems in HConnectionImplementation#locateRegionInMeta if region location is removed from the cache, with large number of client threads we could have many of them getting cache miss and doing meta scan, which looks unnecessary - we could empty mechanism similar to what we have in IdLock in HFileReader to fetch the block to cache, do ensure that if one thread is already looking up location for region R1, other threads who need it's location wait until first thread finishes his work.