[jira] [Commented] (CASSANDRA-4180) Remove 2-phase compaction

["Sylvain Lebresne (Commented) (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-4180?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13258294#comment-13258294 ] 

Sylvain Lebresne commented on CASSANDRA-4180:
---------------------------------------------

I'll note that an initial idea could be to keep the row header as it is (post CASSANDRA-2319), and during compaction to keep the space for the row size and column count, compact all columns, and seek back to write those two values. However, compression forbids us to do that, so we'll have to really remove those part two. However, we can trade the column count by writing a specific marker to mark the end of a row. As for the data size, we can get it from the index.
                
> Remove 2-phase compaction
> -------------------------
>
>                 Key: CASSANDRA-4180
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-4180
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: Sylvain Lebresne
>            Assignee: Sylvain Lebresne
>             Fix For: 1.2
>
>
> LazilyCompactedRow reads all data twice to compact a row which is obviously inefficient. The main reason we do that is to compute the row header. However, CASSANDRA-2319 have removed the main part of that row header. What remains is the size in bytes and the number of columns, but it should be relatively simple to remove those, which would then remove the need for the two-phase compaction.

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