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Sylvain Lebresne commented on CASSANDRA-2319:
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bq. we have the row index_interval measured in rows, but for columns we have
column_index_size_in_kb
Yes, I suppose we could switch the index_interval to the size_in_kb type, which
would better limit the amount of data we may end up reading in the index now
that row index entry may be of more widely different sizes. However, I don't
see an easy way to merge those 2 settings into 1 if that was what you were
hinting to.
bq. So, this isn't quite true
I really just meant that the committed code had no interaction with the
compression code. You are right though that having compression block not
aligned with data boundaries could mean that sometimes we'll have to decompress
one more block that would be strictly necessary, but that's more a drawback of
having compression blocks not being aligned to any data boundaries than
anything related to this actual patch. Don't know how much that matters in
practice though.
> 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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