[jira] [Created] (CASSANDRA-15196) Refactor inheritance around CommitLogSegment management and allocation

["Joshua McKenzie (JIRA)" <ji...@apache.org>]

Joshua McKenzie created CASSANDRA-15196:
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             Summary: Refactor inheritance around CommitLogSegment management and allocation
                 Key: CASSANDRA-15196
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-15196
             Project: Cassandra
          Issue Type: Improvement
          Components: Local/Commit Log
            Reporter: Joshua McKenzie
            Assignee: Joshua McKenzie


Back when I wrote CASSANDRA-8844 and CASSANDRA-12148, a few things about the CommitLog stood out to me that I wasn't in love with. At the time I was much more of the mind of "When in Rome..." regarding some of our structures, our naming, and specifically regarding our penchant for inheritance vs. composition. Turns out I have an itch here I need to scratch.

This patch refactors the CommitLog in a few key ways:
 * Removes inheritence for CommitLogSegmentManagerX, instead has a single CommitLogSegmentManager and a CommitLogSegmentAllocator interface
 ** This interface is implemented by CommitLogSegmentAllocatorStandard and CommitLogSegmentAllocatorCDC
 * Renames a few variables and methods within the segment manager to make their purpose and role more clear from names alone (hopefully):
 ** allocatingFrom --> activeSegment
 ** allocatingFrom() --> getActiveSegment()
 ** advanceAllocatingFrom() – switchToNewSegment()
 ** activeSegments --> unflushedSegments
 ** getActiveSegments --> getUnflushedSegments()
 ** awaitAvailableSegment(...) --> awaitSegmentAllocation(...)
 ** isStillAllocating() --> hasRoom()
 * Reorders some of the "allocation-and-compare-in-while-loop-decl) to more idiomatic style
 * Adds some comments to various under-documented methods, mostly related to CDC and timing

As far as we are in the 4.0 testing, I don't expect this to hit pre 4.0. Given it's a relatively minor refactor in well-tested code, doesn't change functionality, and doesn't impact any of the publicly exposed APIs in the CommitLog ecosystem, I'd be comfortable with it going in a minor release after 4.0 is out. But I'm open to alternative viewpoints.

Have run unit tests locally w/out issue on both regular and cdc-targets; need to get CI against the branch internally for full dtest run and I'll post when it's done. Just wanted to get visibility to this out there in case anyone was curious or thinking of working on the same thing.

[ Link to branch on github|https://github.com/apache/cassandra/compare/trunk...josh-mckenzie:clean_cl_comp]



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