[jira] [Commented] (CASSANDRA-8543) Allow custom code to control behavior of reading and compaction

["Aleksey Yeschenko (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-8543?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14260064#comment-14260064 ] 

Aleksey Yeschenko commented on CASSANDRA-8543:
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bq. When storing series data in blob objects because of speed improvements ...

Don't do that, and you'll no longer have the problem to solve.

Technically, this ticket is a duplicate of CASSANDRA-6412, which is not exactly on our roadmap at the moment. But your real issue is that you are trying to pack those values into blobs. It's bad use of Cassandra - just don't do that.

> Allow custom code to control behavior of reading and compaction
> ---------------------------------------------------------------
>
>                 Key: CASSANDRA-8543
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-8543
>             Project: Cassandra
>          Issue Type: New Feature
>            Reporter: Pavol Slamka
>            Priority: Minor
>
> When storing series data in blob objects because of speed improvements, it is sometimes neccessary to change only few values of a single blob (say few integers out of 1024 integers). Right now one could rewrite these using compare and set and versioning - read blob and version, change few values, write whole updated blob and incremented version if version did not change, repeat the whole process otherwise (optimistic approach). However compare and set brings some overhead. Let's try to leave out compare and set, and instead reading and updating, let's write only "blank" blob with only few values set. Blank blob contains special blank placeholder data such as NULL or max value of int or similar. Since this write in fact only appends new SStable record, we did not overwrite the old data yet. That happens during read or compaction. But if we provided custom read, and custom compaction, which would not replace the blob with a new "sparse blank" blob, but rather would replace values in first blob (first sstable record) with only "non blank" values from second blob (second sstable record), we would achieve fast partial blob update without compare and set on a last write wins basis. Is such approach feasible? Would it be possible to customize Cassandra so that custom code for compaction and data reading could be provided for a column (blob)? 
> There may be other better solutions, but speedwise, this seems best to me. Sorry for any mistakes, I am new to Cassandra.
> Thanks.



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