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From "Josh McKenzie (Jira)" <>
Subject [jira] [Assigned] (CASSANDRA-15196) Refactor inheritance around CommitLogSegment management and allocation
Date Sun, 06 Oct 2019 17:22:00 GMT


Josh McKenzie reassigned CASSANDRA-15196:

    Assignee: Josh McKenzie  (was: Joshua McKenzie)

> Refactor inheritance around CommitLogSegment management and allocation
> ----------------------------------------------------------------------
>                 Key: CASSANDRA-15196
>                 URL:
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Local/Commit Log
>            Reporter: Joshua McKenzie
>            Assignee: Josh McKenzie
>            Priority: Normal
> 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
>  * Adds some comments to various under-documented methods, mostly related to CDC and
> 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|]

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