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From "Keith Turner (JIRA)" <>
Subject [jira] [Commented] (ACCUMULO-1228) Allow clients to disable column families and locality groups
Date Thu, 04 Apr 2013 01:56:13 GMT


Keith Turner commented on ACCUMULO-1228:

bq. I would almost go as far to say that I expect locality groups to be immutable.

I would argue that making this change (encouraging scans against locality groups) would in
fact make locality groups immutable.  Anyone who understands this new client API would be
afraid to make changes to locality group config because they can not predict the consequences.
 Is this what we want?

bq. "why did #3 happen?"

Its a contrived example to illustrate the point that locality groups can be easily changed.
 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.
> 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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