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From "Christopher Tubbs (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (ACCUMULO-1228) Allow clients to disable column families and locality groups
Date Wed, 03 Apr 2013 19:53:15 GMT

    [ https://issues.apache.org/jira/browse/ACCUMULO-1228?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13621261#comment-13621261
] 

Christopher Tubbs commented on ACCUMULO-1228:
---------------------------------------------

For the first proposal, I think it might be useful to add to the API the ability to exclude
columns or column families.

For the second proposal, however, allowing the client to specify details of locality groups
means making locality groups a client-viewable feature, instead of a server-side optimization.
Users don't "fetch a locality group", they query for "data identified by (in this case) a
set of column families", regardless of how it is stored. Blurring the lines between storage
optimization and the data model is confusing and risky, I think it's a bad idea. Further,
it's very poorly defined... would you use the locality group as determined by the current
configuration, or the locality groups specified in the RFiles on disk prior to the last locality
group change? After all, you can get 10 different files with 10 different locality group characteristics...
and this works fine if you ask for the data, but it would be... confusing and unpredictable
from a user's perspective if you ask for a locality group. This is a bit like asking "give
me all data in my files stored with snappy compression vs. gzip".
                
> 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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