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From "Jonathan Ellis (JIRA)" <j...@apache.org>
Subject [jira] Commented: (CASSANDRA-286) slice offset breaks read repair
Date Thu, 09 Jul 2009 16:04:14 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-286?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12729306#action_12729306
] 

Jonathan Ellis commented on CASSANDRA-286:
------------------------------------------

Yes, that's the brute force fix, but it means that in the case of mass deletes in a given
CF we could very possibly OOM collecting all the tombstones for a large offset.

Again, my rule of thumb is: features that allow the user to do something that slow things
down are ok; features that allow the user to crash the server, are not. :)

> slice offset breaks read repair
> -------------------------------
>
>                 Key: CASSANDRA-286
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-286
>             Project: Cassandra
>          Issue Type: Bug
>            Reporter: Jonathan Ellis
>
> [code]
>         int liveColumns = 0;
>         int limit = offset + count;
>         for (IColumn column : reducedColumns)
>         {
>             if (liveColumns >= limit)
>                 break;
>             if (!finish.isEmpty()
>                 && ((isAscending && column.name().compareTo(finish) >
0))
>                     || (!isAscending && column.name().compareTo(finish) <
0))
>                 break;
>             if (!column.isMarkedForDelete())
>                 liveColumns++;
>             if (liveColumns > offset)
>                 returnCF.addColumn(column);
>         }
> [code]
> The problem is that for offset to return the correct "live" columns, it has to ignore
tombstones it scans before the first live one post-offset.
> This means that instead of being corrected within a few ms of a read, a node can continue
returning deleted data indefinitely (until the next anti-entropy pass).
> Coupled with offset's inherent inefficiency (see CASSANDRA-261) I think this means we
should take it out and leave offset to be computed client-side (which, for datasets under
which it was reasonable server-side, will still be reasonable).

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