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From "Josh Elser (JIRA)" <>
Subject [jira] [Commented] (ACCUMULO-1228) Allow clients to disable column families and locality groups
Date Thu, 04 Apr 2013 02:06:14 GMT


Josh Elser commented on ACCUMULO-1228:

bq.  A possible driver for this change would be a new and important use case for which a locality
group change would be beneficial. But actually, they probably would not have made the locality
group config change because of fear of breaking existing code. So the new use case would not
benefit from Accumulo's ability to change locality group config on the fly.

Someone is still making the conscious decision here to alter the locality group. They could've
made a new locality group instead of destroying the original, no?

Actually, I'm a little fuzzy here. Say we have a table with columns [A,B,C,D,E] and LG1=[A,B].
Say [] makes LG2=[C,D]. Now [~kturner] changes LG1 from [A,B] to
[A,B,C]. Would my "column search space" for specifying LG1 be [A,B,C,D] because of the overlap
of LG1 and LG2? What happens here after a compaction? Would LG1 and LG2 share a common "file"
that contains C or would LG1 "contain" all of LG2 and vice-versa because of the overlap? Am
I missing the joke here?
> Allow clients to disable column families and locality groups
> ------------------------------------------------------------
>                 Key: ACCUMULO-1228
>                 URL:
>             Project: Accumulo
>          Issue Type: New Feature
>          Components: client, tserver
>    Affects Versions: 1.5.0
>            Reporter: William Slacum
>            Priority: Minor
>             Fix For: 1.6.0
> There's an inconsistency between what a server is capable of and what a client can tell
it to do with respect to fetching column families.
> Currently, a user can tell a {{Scanner}} to fetch some set of column families. The iterators
support not only this, but also the converse where a user does not want to retrieve column
families. An iterator implementation can do this by hand, but a client cannot specifically
tell a Scanner to not return data from a set of column families. Clients should be able to
specify this option.
> There also seems to be an inconsistency with how locality groups are defined and then
utilized. If I want to specify a set of column families as being part of a locality group,
I have to provide a mapping of locality group name to a list of column families. If I want
to fetch a locality group, I have to get the mapping first, rather than just set which locality
group I want to use. It'd be more convenient to tell the scanner just to fetch which locality
groups I want, and have the server know which column families that means.

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