[jira] [Comment Edited] (CASSANDRA-4304) Add bytes-limit clause to queries

["Christian Spriegel (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-4304?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13405054#comment-13405054 ] 

Christian Spriegel edited comment on CASSANDRA-4304 at 7/6/12 11:29 AM:
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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-4415 could use a bytes pagesize too internally
- 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.

                
      was (Author: christianmovi):
    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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