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From Jan Lehnardt <>
Subject Re: Some extra opinions for Mango Index Selection Fallback
Date Fri, 24 Nov 2017 16:38:19 GMT
I’m +1 as well.

Not to derail this particular discussion (but watch me do it anyway ;):
it be great if we could add a metric akin to “slow queries” that gets
incremented every time we do the fallback. Ideally then this could be
shown in Fauxton is growing steadily, and external monitoring can look
at is as well.

I’m totally fine with this landing as-is, and adding the metric later
as long as we keep an open issue for that. Would make a nice first time
contribution, too.


> On 22. Nov 2017, at 21:38, Tony Sun <> wrote:
> Hello Everyone,
> Will and I were hoping to get some more opinions for
> To provide some context, Mango had a long existing bug that allowed users
> to incorrectly use an index for a query. This bug was fixed in
> However, this fix can lead to a
> breaking change for users who incorrectly used the index prior to the fix.
> Instead of results being returned, the user will see a "no_usable_index"
> error.
> PR 962 mitigates this issue by essentially removing "no_usable_index".
> We either find another usable index, or perform a full table scan via
> _all_docs.
> Should we allow this new behavior or continue to throw errors and force
> users to create a new index?
> Happy Holidays!
> Tony

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