[HBASE-9272] A parallel, unordered scanner

• Type: New Feature
• Status: Closed
• Priority: Minor
• Resolution: Won't Fix
• Assignee: Unassigned
• Reporter: Lars Hofhansl
• Created: 20/Aug/13 17:40
• Updated: 16/Jun/22 17:53
• Resolved: 24/Dec/19 20:10

Description

The contract of ClientScanner is to return rows in sort order. That limits the order in which region can be scanned.
I propose a simple ParallelScanner that does not have this requirement and queries regions in parallel, return whatever gets returned first.

This is generally useful for scans that filter a lot of data on the server, or in cases where the client can very quickly react to the returned data.

I have a simple prototype (doesn't do error handling right, and might be a bit heavy on the synchronization side - it used a BlockingQueue to hand data between the client using the scanner and the threads doing the scanning, it also could potentially starve some scanners long enugh to time out at the server).
On the plus side, it's only a 130 lines of code.

Issue Links

• relates to: HBASE-1935 Scan in parallel