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