Re: Re: [RFC] [PATCH] Flexible "partition pruning" hook

Hi Peter,

On 2/28/19 10:36 PM, Mike Palmiotto wrote:
> On Wed, Feb 27, 2019 at 12:36 PM Peter Eisentraut
> <peter(dot)eisentraut(at)2ndquadrant(dot)com> wrote:
>> <snip>
>> To rephrase this: You have a partitioned table, and you have a RLS
>> policy that hides certain rows, and you know based on your business
>> logic that under certain circumstances entire partitions will be hidden,
>> so they don't need to be scanned. So you want a planner hook that would
>> allow you to prune those partitions manually.
>>
>> That sounds pretty hackish to me. We should give the planner and
>> executor the appropriate information to make these decisions, like an
>> additional partition constraint.
>
> Are you thinking of a partition pruning step for FuncExpr's or
> something else? I was considering an implementation where FuncExpr's
> were marked for execution-time pruning, but wanted to see if this
> patch got any traction first.
>
>> If this information is hidden in
>> user-defined functions in a way that cannot be reasoned about, who is
>> enforcing these constraints and how do we know they are actually correct?
>
> The author of the extension which utilizes the hook would have to be
> sure they use the hook correctly. This is not a new or different
> concept to any other existing hook. This hook in particular would be
> used by security extensions that have some understanding of the
> underlying security model being implemented by RLS.

Thoughts on Mike's response?

Regards,
--
-David
david(at)pgmasters(dot)net