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From "Jonathan Ellis (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-4180) Single-pass compaction for LCR
Date Mon, 01 Apr 2013 14:21:16 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-4180?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13618794#comment-13618794
] 

Jonathan Ellis commented on CASSANDRA-4180:
-------------------------------------------

Sorry, I got caught up in this over the weekend since the more I dug on CASSANDRA-5344 the
more it looked like I was actually solving this first.  I've pushed my first draft to github.com/jbellis/cassandra/tree/4180.

I see DefsTest fail occasionally but it is not 100% reproducible, so I'm not sure if it was
caused by my changes.  I also see CFSTest log errors sometimes but that one is definitely
not related (CASSANDRA-5410).

(Testing was a bitch at first since sstable errors would just cause the schema loader to break
violently; hence the option I added to just inject the schema directly, without going through
the migration path.  That allowed enough tests to run to track down the problems.)

Everything was fairly straightforward except SSTableScanner.  (Sounds like the same thing
Jason ran into.)  I simplified things by noting that seekTo was only used to initialize the
scanner to a certain starting point, so I pulled that into the constructor to make seeking
mid-iteration a non-concern.  (This also allowed removing SSTableBoundedScanner.)  I also
merged KeyScanningIterator and FilteringKSI; FKSI already had most of the code needed to compute
data size from the index entries, which compaction needed to decide whether to use an eager
or lazy approach.

There were a lot of places that just one-off sstable reading that were easy to miss.  This
smells fishy to me but it wasn't obvious how to re-organize things to make it unnecessary,
so I haven't tried to solve that here.

I also haven't tried to update scrub for the new format.
                
> Single-pass compaction for LCR
> ------------------------------
>
>                 Key: CASSANDRA-4180
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-4180
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: Sylvain Lebresne
>            Assignee: Jason Brown
>              Labels: compaction
>             Fix For: 2.0
>
>
> 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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