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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 14:35:15 GMT


Josh Elser commented on ACCUMULO-1228:

Perhaps that would satisfy the requirement. Ultimately, I want a client to be able to just
say "Give me these columns!". My thought was that "well, a client may know of columns from
many ways". Hypothetically, 

fetchColumns(new Column[] {new Column("c1"), new Column("c2"), new LocalityGroup("lg1")})

>From an interface perspective, having something like a scan profile, which would encompass
the collection of columns regardless of how one might define that collection of columns, would
satisfy my want from the API and, it seems, avoid concerns about the mutability of locality
groups and unaware clients. Perhaps a happy medium would be to work towards being able to
fetch data using a collection of columns to fetch (using *only* the column name, not locality
group) or using a scan profile which could create a short-hand for clients to include/exclude
many columns. I think I like that idea.
> 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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