Re: why partition pruning doesn't work?

On 6 June 2018 at 03:07, David Rowley <david(dot)rowley(at)2ndquadrant(dot)com> wrote:
> Please see the attached patch. I've only just finished with it and
> it's not fully done yet as there's still an XXX comment where I've not
> quite thought about Exprs with Vars from higher levels. These might
> always be converted to Params, so the code might be okay as is, but
> I've not checked this yet, hence the comment remains.

I looked at this again today and decided that the XXX comment could
just be removed. I also changed contains_only_safeparams into
contains_unsafeparams and reversed the condition. I then decided that
I didn't like the way we need to check which params are in the Expr
each time we call partkey_datum_from_expr. It seems better to prepare
this in advance when building the pruning steps. I started work on
that, but soon realised that I'd need to pass a List of Bitmapsets to
the executor. This is a problem as Bitmapset is not a Node type and
cannot be copied with COPY_NODE_FIELD(). Probably this could be
refactored to instead of passing 3 Lists in the PartitionPruneStepOp
we could invent a new node type that just has 3 fields and store a
single List.

Anyway, I didn't do that because I'm not sure what the fate of this
patch is going to be. I'd offer to change things around to add a new
Node type, but I don't really want to work on that now if this is v12
material.

I've attached a cleaned up version of the patch I posted yesterday.

--
David Rowley http://www.2ndQuadrant.com/
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