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From "Adam Fuchs (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (ACCUMULO-227) Improve in memory map counts to provide cell level uniqueness for repeated columns in mutation
Date Wed, 21 Dec 2011 22:49:30 GMT

    [ https://issues.apache.org/jira/browse/ACCUMULO-227?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13174469#comment-13174469
] 

Adam Fuchs commented on ACCUMULO-227:
-------------------------------------

This is an extremely rare edge case, but not quite so rare that nobody has seen it. By default,
Accumulo tables use a versioning iterator that keeps the latest version. Only keeping one
of the values assigned to a given key within a mutation preserves this behavior. However,
when we configure a summing aggregator on a table we would probably expect to see contributions
from all of the entries in a mutation, so the current behavior goes against our expectations
in that case. Aggregating on the client side would be one solution, but that would involve
a big change to the semantics of when and where iterators run, as well as a lot of work building
an iterator framework that works on the client side. We already have the plumbing of supporting
multiple identical entries to support isolation. This is a rare enough problem that performance
will not be a concern, so I think the simple solution to this particular problem is the one
that is described.
                
> Improve in memory map counts to provide cell level uniqueness for repeated columns in
 mutation
> -----------------------------------------------------------------------------------------------
>
>                 Key: ACCUMULO-227
>                 URL: https://issues.apache.org/jira/browse/ACCUMULO-227
>             Project: Accumulo
>          Issue Type: Improvement
>          Components: tserver
>            Reporter: John Vines
>            Assignee: John Vines
>             Fix For: 1.5.0
>
>
> Currently for isolation we only isolate mutations. This doesn't allow mutations with
identical cells within it. We should increase the mutation counts to account for each individual
cell instead of each mutation.

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