Chetan Mehrotra commented on OAK-937:

bq.  For example, each index can have a multi-valued property "tags". Then a 
query can specify "option(index tag <x>)".

+1. This allows customer to bind to specific index or enable QE to select from 
a set of indexes.

[~catholicon] Regarding the aggregate - There are other cases also like custom 
synonyms, analyzer configured for same nodetype. So its best to do selection at 
index level instead.

> Query engine index selection tweaks: shortcut and hint
> ------------------------------------------------------
>                 Key: OAK-937
>                 URL: https://issues.apache.org/jira/browse/OAK-937
>             Project: Jackrabbit Oak
>          Issue Type: Improvement
>          Components: query
>            Reporter: Alex Deparvu
>            Assignee: Thomas Mueller
>            Priority: Critical
>              Labels: performance
>             Fix For: 1.8
> This issue covers 2 different changes related to the way the QueryEngine 
> selects a query index:
>  Firstly there could be a way to end the index selection process early via a 
> known constant value: if an index returns a known value token (like -1000) 
> then the query engine would effectively stop iterating through the existing 
> index impls and use that index directly.
>  Secondly it would be nice to be able to specify a desired index (if one is 
> known to perform better) thus skipping the existing selection mechanism (cost 
> calculation and comparison). This could be done via certain query hints [0].
> [0] http://en.wikipedia.org/wiki/Hint_(SQL)

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