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From "Sean Busbey (JIRA)" <>
Subject [jira] [Commented] (ACCUMULO-3089) Create a volume chooser that makes decisions based on table attributes
Date Wed, 22 Oct 2014 04:44:34 GMT


Sean Busbey commented on ACCUMULO-3089:

[~ctubbsii] wrote:
Sean Busbey wrote:
bq. Just as a simple example, limiting volumes to particular namespaces would not require
changing when table properties are available. It would also not require changing the table
creation api.

Oh, I see. Yes, absolutely, that would be a simpler example. Certainly, that could be done,
but I don't see how useful it would be. Without any environment, the only choosers possible
are ones that have hard-coded decisions, which would have to be recompiled when the policy
changes, or who rely on external/remote services for configuration. (This is true of the namespace
example, for instance... because there is no way for the chooser to know which namespace it
is making a decision for.) None of our other pluggable components have such limitations, and
we've made it possible to configure each through environment (usually table properties, as
in the case of iterators, constraints, etc.), so I don't see why this addition should be vetoed

So, yes, that's a simpler example... but it's not an example which satisfies the criteria
of this ticket, because this ticket is essentially about creating an example which can make
smarter decisions, based on configuration.

It could make use of configuration because no tablets have to be written on a particular volume
at the time of namespace creation. So, for example, you could

* create namespace X
* add a config to namespace X that said something like "only use volume1 and volume2"
* create a table Y in namespace X
* see that tablets for table X:Y are only on volume 1 and volume 2

AFAICT, this kind of implementation can solve all the use cases given.

> Create a volume chooser that makes decisions based on table attributes
> ----------------------------------------------------------------------
>                 Key: ACCUMULO-3089
>                 URL:
>             Project: Accumulo
>          Issue Type: Improvement
>            Reporter: Christopher Tubbs
>            Assignee: Jenna Huston
> Use case:
> User provisions multiple volumes, some with tmpfs drives, some with SSDs, some with traditional
magnetic spindle hard drives. A volume chooser could use attribute information on tables (ACCUMULO-2841)
to decide which volume to choose when creating new tablets.

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