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From "Stefania (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-7066) Simplify (and unify) cleanup of compaction leftovers
Date Tue, 11 Aug 2015 08:56:46 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-7066?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14681468#comment-14681468
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Stefania commented on CASSANDRA-7066:
-------------------------------------

Hi Benedict, thank you for your review. 

I still need to self-review this and check CI results tomorrow, but if you want to quickly
review in parallel to speed things up here is what I've done:

* Added a new ABORT record that we use in {{TransactionTidier}} before removing unfinished
leftovers of a 'live' transaction whose files are about to be deleted. We *still assume abort
unless there is a COMMIT record* when getting temporary files or when cleaning up on startup.
Is this what you intended?

* Moved transaction log files to the same folder as the sstable files and renamed them to
{{ma_txt_optype_id.log}} where {{ma}} is the latest sstable version. This ensures the txn
logs sort at the end. When upgrading we will not recognize transactions for tables in an old
format, which I assume is also a good thing?

* Implemented unified listing of files using {{[newDirectoryStream|http://docs.oracle.com/javase/7/docs/api/java/nio/file/Files.html#newDirectoryStream(java.nio.file.Path)]}},
which allows us to check if the stream is atomic by checking if we have an instance of {{[SecureDirectoryStream|http://docs.oracle.com/javase/7/docs/api/java/nio/file/SecureDirectoryStream.html]}},
third paragraph in the documentation of {{newDirectoryStream}}.

For the sake of clearness, once this ticket is committed, people currently running 3.0 will
have to wipe the data folder, due to the compression metadata format changes and to the fact
that old transaction log files will be ignored and will not get deleted automatically.


> Simplify (and unify) cleanup of compaction leftovers
> ----------------------------------------------------
>
>                 Key: CASSANDRA-7066
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-7066
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: Benedict
>            Assignee: Stefania
>            Priority: Minor
>              Labels: benedict-to-commit, compaction
>             Fix For: 3.0 alpha 1
>
>         Attachments: 7066.txt
>
>
> Currently we manage a list of in-progress compactions in a system table, which we use
to cleanup incomplete compactions when we're done. The problem with this is that 1) it's a
bit clunky (and leaves us in positions where we can unnecessarily cleanup completed files,
or conversely not cleanup files that have been superceded); and 2) it's only used for a regular
compaction - no other compaction types are guarded in the same way, so can result in duplication
if we fail before deleting the replacements.
> I'd like to see each sstable store in its metadata its direct ancestors, and on startup
we simply delete any sstables that occur in the union of all ancestor sets. This way as soon
as we finish writing we're capable of cleaning up any leftovers, so we never get duplication.
It's also much easier to reason about.



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