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From "Christopher Tubbs (JIRA)" <>
Subject [jira] [Commented] (ACCUMULO-3294) Need mechanism to update iterator settings
Date Sun, 15 Nov 2015 08:32:11 GMT


Christopher Tubbs commented on ACCUMULO-3294:

We already have the ability to manually modify individual properties. However, it does require
one to be familiar with how the serialization of iterators occurs in a table's configuration.

[~kturner] and I were chatting about a related item the other day, regarding ACCUMULO-4050
ideas, because we can't really offer consistency across scans for iterator settings, even
if we enable atomic updates to a batch of configuration items. At the most, that buys us per
scan session atomicity (within a tablet server), but not per-scan atomicity. In that discussion,
it was suggested that we might want to urge users to prefer scan-time iterators over table-configured
iterators. And, the table-configured iterators that we do offer, should really be used sparingly,
reserved for privileged user decisions about how that table should be presented (more like
a "view" in an RDBMS, but with a 1-to-1 mapping between the view and the dataset, instead
of a many-to-1), with the full understanding of the potential side-effects and pitfalls that
alterations can have due to lack of atomicity across the cluster.

Given all that, I'm not sure it's necessarily a good idea to add new APIs to manage the table-configured
iterators in ways that might enable users to shoot themselves in the foot. The current solution
to this use case is to remove an entire iterator and reapply it with new configuration. That
currently only carries slightly less risk, though (much less after ACCUMULO-4050). This might
warrant further discussion. Obviously, if this is useful, I'm not going to be opposed to it...
but I think it warrants caution.

> Need mechanism to update iterator settings
> ------------------------------------------
>                 Key: ACCUMULO-3294
>                 URL:
>             Project: Accumulo
>          Issue Type: Improvement
>          Components: client
>            Reporter: John Vines
>            Assignee: Jonathan Park
>             Fix For: 1.8.0
>         Attachments: bug3294.patch, bug3294.patch.1
> Currently our API supports attachIterator, removeIterator, and getIteratorSettings. There
is no mechanism to directly change an iterators settings.

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