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Christian Spriegel commented on CASSANDRA-4304:
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Hi Jonathan, I agree with you that operator limits are useful. Nevertheless my
use-case (mobile devices asking for the next chunk of data) would benefit from
a client-defined limit. This way, a call from a mobile could be handled in a
single cassandra-request.
There are probably many more areas where such a feature would be useful:
- Hectors ColumnSliceIterator could use it. Currently it loads batches of 100
items.
- Cassandra could maybe use it internally too, e.g. HintedHandoffManager
calculates a limit based on the average column size. This could be simply
replaced by a batch size in bytes.
- Anything that slices through blobs with variable sizes. (e.g. my blobs are
varying between 100bytes and 5MB)
I think this should be a pretty low hanging fruit, which can do very little
damage. Imho the only ugly thing is that it requires a new attribute in the
Thrift-Api/CQL/CLI.
> Add bytes-limit clause to queries
> ---------------------------------
>
> Key: CASSANDRA-4304
> URL: https://issues.apache.org/jira/browse/CASSANDRA-4304
> Project: Cassandra
> Issue Type: New Feature
> Components: API, Core
> Reporter: Christian Spriegel
> Fix For: 1.2
>
> Attachments: TestImplForSlices.patch
>
>
> Idea is to add a second limit clause to (slice)queries. This would allow easy
> loading of batches, even if content is variable sized.
> Imagine the following use case:
> You want to load a batch of XMLs, where each is between 100bytes and 5MB
> large.
> Currently you can load either
> - a large number of XMLs, but risk OOMs or timeouts
> or
> - a small number of XMLs, and do too many queries where each query usually
> retrieves very little data.
> With cassandra being able to limit by size and not just count, we could do a
> single query which would never OOM but always return a decent amount of data
> -- with no extra overhead for multiple queries.
> Few thoughts from my side:
> - The limit should be a soft limit, not a hard limit. Therefore it will
> always return at least one row/column, even if that one large than the limit
> specifies.
> - HintedHandoffManager:303 is already doing a
> InMemoryCompactionLimit/averageColumnSize to avoid OOM. It could then simply
> use the new limit clause :-)
> - A bytes-limit on a range- or indexed-query should always return a complete
> row
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