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https://issues.apache.org/jira/browse/CASSANDRA-172?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Jun Rao updated CASSANDRA-172:
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Attachment: get_slice_from.patchv2
Attache patch v2.
1. Renamed <start, count> to <offset, limit>. Also set the default value of
offset to 0 since that is likely the common usage. In general, the offset
parameter allows one to efficiently implement scrolling to an arbitrary
positition of the returned results. This kind of functionality is more
efficient if provided on the server side.
3. On second thought, I don't think the descending ordering necessarily
introduces extra disk seeks. This is because each SSTable is always accessed
one block at a time, independent of the ordering. A block is always asked
sequentially and therfore, there is likely just one seek for the whole block.
Across blocks, there are likely seeks, again independent of the ordering. This
is because we access all SSTables interleavingly. So, keep the ordering option
since it makes this api more general.
4. Switched from CF iterator to Column iterator and reused the CF template for
all columns iterated.
5. ColumnSliceBlockReader still returns CF + columns. The CF deserialization
overhead is amortized among a block of columns and shouldn't be too much. This
api can stay simple this way.
Addressed the rest of the comments and rebased the code.
> A improved and more general version of get_slice
> ------------------------------------------------
>
> Key: CASSANDRA-172
> URL: https://issues.apache.org/jira/browse/CASSANDRA-172
> Project: Cassandra
> Issue Type: New Feature
> Reporter: Jun Rao
> Assignee: Jun Rao
> Fix For: 0.4
>
> Attachments: get_slice_from.patchv1, get_slice_from.patchv2
>
>
> Today, get_slice has to scan through all columns in every memtable and
> sstable to get a slice of columns. This becomes inefficient when the number
> of columns in a row is large. We need a more efficient API.
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