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https://issues.apache.org/jira/browse/CASSANDRA-2319?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13254707#comment-13254707
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Sylvain Lebresne commented on CASSANDRA-2319:
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I still don't see how that would make us remove one of the 2 config option
we're talking about. Even if you basically switch to an on-disk format where
there is no notion of Row, you still have to (1) say how big are the block you
index in the index file, and (2) how much of those index entries you load in
memory (unless you decide to load the full index in memory, but I don't think
that's what we're talking about). I.e. the ??raison d'être?? of both
index_interval and column_index_size_in_kb is *not* because we have the notion
of rows in the on-disk format.
Don't get me wrong, I'm not saying that having a file format where the row key
is not special anymore is a bad idea at all (though I'll admit that I'm less
convinced that moving C* to such a file format should be a priority), but it
seems to me that it's a completely different debate.
> Promote row index
> -----------------
>
> Key: CASSANDRA-2319
> URL: https://issues.apache.org/jira/browse/CASSANDRA-2319
> Project: Cassandra
> Issue Type: Improvement
> Components: Core
> Reporter: Stu Hood
> Assignee: Sylvain Lebresne
> Labels: index, timeseries
> Fix For: 1.2
>
> Attachments: 2319-v1.tgz, 2319-v2.tgz, promotion.pdf, version-f.txt,
> version-g-lzf.txt, version-g.txt
>
>
> The row index contains entries for configurably sized blocks of a wide row.
> For a row of appreciable size, the row index ends up directing the third seek
> (1. index, 2. row index, 3. content) to nearby the first column of a scan.
> Since the row index is always used for wide rows, and since it contains
> information that tells us whether or not the 3rd seek is necessary (the
> column range or name we are trying to slice may not exist in a given
> sstable), promoting the row index into the sstable index would allow us to
> drop the maximum number of seeks for wide rows back to 2, and, more
> importantly, would allow sstables to be eliminated using only the index.
> An example usecase that benefits greatly from this change is time series data
> in wide rows, where data is appended to the beginning or end of the row. Our
> existing compaction strategy gets lucky and clusters the oldest data in the
> oldest sstables: for queries to recently appended data, we would be able to
> eliminate wide rows using only the sstable index, rather than needing to seek
> into the data file to determine that it isn't interesting. For narrow rows,
> this change would have no effect, as they will not reach the threshold for
> indexing anyway.
> A first cut design for this change would look very similar to the file format
> design proposed on #674:
> http://wiki.apache.org/cassandra/FileFormatDesignDoc: row keys clustered,
> column names clustered, and offsets clustered and delta encoded.
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