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From Julian Hyde <>
Subject Re: Documentation around writing a custom cost factory
Date Mon, 20 Mar 2017 16:43:02 GMT

> On Mar 20, 2017, at 12:14 AM, Hussain Pirosha <> wrote:
> Thanks Julian.
> Spending more time with calcite code on computing cost, I have few questions.
> 1. The cost of the plan is the sum of all the  converted (datasource specific) RelNodes

Yes. The cost of a plan is the sum of the costs of its constituent RelNodes.

> 2. the computeSelfCost method shall calculate the cost by using the RelMetaDataQuery.
Can you point to some example or impl where RelMetaData has been implemented or can be used
as a reference?

Not sure what you mean. There is no “RelMetaData” class or interface.

RelMetadataTest should give you some clues (especially if you run it in a debugger).

I’m not the best person to write the documentation you need. Has anyone implemented a metadata
provider in a project that uses Calcite? If so, please share what worked.


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