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From "Aleksey Yeschenko (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-4542) add atomic_batch_mutate method
Date Sat, 08 Sep 2012 19:04:07 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-4542?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13451394#comment-13451394
] 

Aleksey Yeschenko commented on CASSANDRA-4542:
----------------------------------------------

Had a look at possibility of flush optimization. Not sure in can be done in a clean way.

Memtable#writeSortedContents already has an optimization for cf-level deletions - it won't
write the obsolete columns, only the cf-level tombstone.
As the comment in there says, it's not safe to not write the tombstone even if it's already
past the gc grace period (the row might have columns in other sstables and they won't be removed
at compaction if we never write the cf-tombstone).
It can only be omitted if we know for sure that there are no columns for this row in any sstables
and it's a tricky thing, esp. when you count in remote nodes.

There is a different way though. batchlog is local and each write comes with a new random
uuid as key. So if there is a row in the memtable then we know that there are no columns for
the row in any sstables and can safely dismiss the tombstone write as well - this will require
some API changes to CFS/Memtable though. 

                
> add atomic_batch_mutate method
> ------------------------------
>
>                 Key: CASSANDRA-4542
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-4542
>             Project: Cassandra
>          Issue Type: Sub-task
>          Components: API, Core
>            Reporter: Jonathan Ellis
>            Assignee: Aleksey Yeschenko
>             Fix For: 1.2.1
>
>         Attachments: 4542-diff.txt, 4542-v4.txt, 4542-v5.patch, CASSANDRA-4542-4543-4544-v3.patch
>
>
> atomic_batch_mutate will have the same parameters as batch_mutate, but will write to
the batchlog before attempting distribution to the batch rows' replicas.

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