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From "Kelvin Kakugawa (JIRA)" <>
Subject [jira] Commented: (CASSANDRA-1546) (Yet another) approach to counting
Date Mon, 04 Oct 2010 12:03:34 GMT


Kelvin Kakugawa commented on CASSANDRA-1546:

I'm a little wary of having "bad" state on disk, because it introduces additional variables
that have to be reasoned about.

As of 2 months ago, AES doesn't perform a read-only major compaction like it did in 0.6. 
It streams across the relevant subsections of each SST on disk to the target node, which is
concatenated into a new SST.  So, if:
1) A streams an AES repair SST to B,
2) that streamed SST is never transformed (e.g. via compaction), then
3) B streams an AES repair SST back to A.

It will send the untransformed columns from A, back to A.  When I have time, I'll re-read
the compaction code to make sure this hasn't changed.

I believe you're right that #1072 also suffers from this potential race condition during reads,
but I'd have to review that code path.

I'm definitely in favor of moving the metadata into a different CF.  Of interest, since all
the columns have the same TTL, a modified compaction strategy could be implemented that completely
deletes the SSTs for this CF w/o inspection based on when the SST was written.

I'll read through your v2 patch.  Thanks for rebasing.

> (Yet another) approach to counting
> ----------------------------------
>                 Key: CASSANDRA-1546
>                 URL:
>             Project: Cassandra
>          Issue Type: New Feature
>          Components: Core
>            Reporter: Sylvain Lebresne
>            Assignee: Sylvain Lebresne
>             Fix For: 0.7.0
>         Attachments: 0001-Remove-IClock-from-internals.patch, 0001-v2-Remove-IClock-from-internals.patch,
0002-Counters.patch, 0002-v2-Counters.patch, 0003-Generated-thrift-files-changes.patch, 0003-v2-Thrift-changes.patch
> This could be described as a mix between CASSANDRA-1072 without clocks and CASSANDRA-1421.
> More details in the comment below.

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