[KUDU-3214] Parallelize DownloadWAL in tablet copy operations

• Type: New Feature
• Status: Resolved
• Priority: Minor
• Resolution: Fixed
• Fix Version/s: 1.14.0
• Component/s: consensus, tablet
• Target Version/s: 1.14.0
• Assignee: wangningito
• Reporter: wangningito
• Created: 16/Nov/20 04:31
• Updated: 27/Nov/20 13:20
• Resolved: 27/Nov/20 13:20

Description

When downloading tablet data via tablet copy operation, it is necessary to download blocks data and wal data.
In KUDU-1728 the DownloadBlocks were parallelized.
However, to intuition, it may make senses to make DownloadWALs parallelized as well. It requires very strict performance tests and correctness guarantee to determine whether to have parallelized version DownloadWALs or not.