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From "Keith Turner (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (ACCUMULO-1228) Allow clients to disable column families and locality groups
Date Thu, 04 Apr 2013 01:28:14 GMT

    [ https://issues.apache.org/jira/browse/ACCUMULO-1228?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13621628#comment-13621628
] 

Keith Turner commented on ACCUMULO-1228:
----------------------------------------

I agree w/ [~ctubbsii] and think a using locality groups for queries is a bad a idea.   Consider
the following events.

 # locality group LG1=CF1,CF2,CF3 is defined
 # user writes code that scans LG1
 # its determined that LG1=CF1,CF2 and LG2=CF3 is a more optimal configuration for some important
use cases, so this config change is made
 # code that scans LG1 breaks

In the contrived example above, if the code had scanned over CF1,CF2,CF3 instead of LG1, then
it would have continued to work after the locality group configuration change.


                
> Allow clients to disable column families and locality groups
> ------------------------------------------------------------
>
>                 Key: ACCUMULO-1228
>                 URL: https://issues.apache.org/jira/browse/ACCUMULO-1228
>             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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