| From: | Andres Freund <andres(at)anarazel(dot)de> |
|---|---|
| To: | Thomas Munro <thomas(dot)munro(at)enterprisedb(dot)com> |
| Cc: | David Fetter <david(at)fetter(dot)org>, Andrew Gierth <andrew(at)tao11(dot)riddles(dot)org(dot)uk>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Early WIP/PoC for inlining CTEs |
| Date: | 2018-08-08 05:02:11 |
| Message-ID: | 20180808050211.ep44572t4lsqj35g@alap3.anarazel.de |
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| Thread: | |
| Lists: | pgsql-hackers |
Hi,
On 2018-08-08 16:55:22 +1200, Thomas Munro wrote:
> On Fri, Jul 27, 2018 at 8:10 PM, David Fetter <david(at)fetter(dot)org> wrote:
> > On Fri, Jul 27, 2018 at 02:55:26PM +1200, Thomas Munro wrote:
> >> On Thu, Jul 26, 2018 at 7:14 AM, David Fetter <david(at)fetter(dot)org> wrote:
> >> > Please find attached the next version, which passes 'make check'.
> >>
> >> ... but not 'make check-world' (contrib/postgres_fdw's EXPLAIN is different).
> >
> > Please find attached a patch that does.
> >
> > It doesn't always pass make installcheck-world, but I need to sleep
> > rather than investigate that at the moment.
>
> One observation I wanted to share: CTE scans inhibit parallelism today
> (something we might eventually want to fix with shared tuplestores).
> This patch therefore allows parallelism in some WITH queries, which
> seems like a very valuable thing.
Might be interesting to see how big a difference it makes for
TPC-DS. Currently the results are bad (as in many queries don't finish
in a relevant time) because it uses CTEs so widely, and there's often
predicates outside the CTE that could be pushed down.
- Andres
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