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From Mike Drob <md...@apache.org>
Subject Re: [DISCUSS] Periodic table exports
Date Fri, 14 Jul 2017 17:46:46 GMT
What's the risk that we are trying to address?

Storing data locally won't help in case of a namenode failure. If you have
a failure that's severe enough to actually kill blocks but not severe
enough that your HDFS is still up, that's a pretty narrow window.

How do you test that your backups are good? That you haven't lost any data
there? Or is it a set and forget (and pray?)

This seems like something that is not worth while to automate because
everybody is going to have such different needs. Write a blog post, then
push people onto existing backup/disaster recovery solutions, including off
site storage, etc. If they're not already convinced that they need this,
then their data likely isn't that valuable to begin with. If this same
problem happens multiple times to the same user... I don't think a periodic
export table will help them.

Mike

On Fri, Jul 14, 2017 at 12:29 PM, Christopher <ctubbsii@apache.org> wrote:

> I saw a user running a very old version of Accumulo run into a pretty
> severe failure, where they lost an HDFS block containing part of their root
> tablet. This, of course, will cause a ton of problems. Without the root
> tablet, you can't recover the metadata table, and without that, you can't
> recover your user tables.
>
> Now, you can recover the RFiles, of course... but without knowing the split
> points, you can run into all sorts of problems trying to restore an
> Accumulo instance from just these RFiles.
>
> We have an export table feature which creates a snapshot of the split
> points for a table, allowing a user to relatively easily recover from a
> serious failure, provided the RFiles are available. However, that requires
> a user to manually run it on occasion, which of course does not happen by
> default.
>
> I'm interested to know what people think about possibly doing something
> like this internally on a regular basis. Maybe hourly by default, performed
> by the Master for all user tables, and saved to a file in /accumulo on
> HDFS?
>
> The closest think I can think of to this, which has saved me more than
> once, is the way Chrome and Firefox backup open tabs and bookmarks
> regularly, to restore from a crash.
>
> Users could already be doing this on their own, so it's not really
> necessary to bake it in... but as we all probably know... people are really
> bad at customizing away from defaults.
>
> What are some of the issues and trade-offs of incorporating this as a
> default feature? What are some of the issues we'd have to address with it?
> What would its configuration look like? Should it be on by default?
>
> Perhaps a simple blog describing a custom user service running alongside
> Accumulo which periodically runs "export table" would suffice? (this is
> what I'm leaning towards, but the idea of making it default is compelling,
> given the number of times I've seen users struggle to plan for or respond
> to catastrophic failures, especially at the storage layer).
>

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