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From Jason Altekruse <altekruseja...@gmail.com>
Subject Making Drill support graceful downgrades
Date Tue, 29 Dec 2015 18:10:46 GMT
While generally Drill has been getting more and more stable with the last
few releases, sometimes users need to downgrade for a variety of reasons.
Currently we have Jackson configured to strictly expect only the current
version of a storage or format plugin configuration.

Here is a recent example of a user who ran into this issue:
https://issues.apache.org/jira/browse/DRILL-4231

I think we should either catch errors like this and suggest that users
check their configuration stored in zookeeper, or in the /tmp/ directory if
running in embedded mode.

Another possible change that could be made to help mitigate this issue
going forward is to change the Jackson configuration to ignore unrecognized
fields in the configuration file. As we will be adding additional
configuration options as we try to accommodate more diverse use cases I
think this could be a small but useful change.

Are there any downsides to changing the behavior in this way? The one I can
think is that someone that would update a configuration after a downgrade
would lose their changes to any new properties from the previously
installed newer version. Considering the behavior currently requires
blowing away the configuration to allow Drill to start up after a
downgrade, this doesn't seem like much of an issue.

Thoughts welcome, I'll open a JIRA if there is no opposition.

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