Re: Add semi-join pushdown to postgres_fdw

Hi.

I took a quick look at the patch. It needs a rebase, although it applies
fine using patch.

A couple minor comments:

1) addl_conds seems a bit hard to understand, I'd use either the full
wording (additional_conds) or maybe extra_conds

2) some of the lines got quite long, and need a wrap

3) unknown_subquery_rels name is a bit misleading - AFAIK it's the rels
that can't be referenced from upper rels (per what the .h says). So they
are known, but hidden. Is there a better name?

4) joinrel_target_ok() needs a better comment, explaining *when* the
reltarget is safe for pushdown. The conditions are on the same row, but
the project style is to break after '&&'.

Also, I'd write

if (!IsA(var, Var))
continue;

which saves one level of nesting. IMHO that makes it more readable.

regards

--
Tomas Vondra
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