Horton

Re: Asynchronous Append on postgres_fdw nodes.

Andrei Lepikhov <a.lepikhov@postgrespro.ru>

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From: "Andrey V. Lepikhov" <a.lepikhov@postgrespro.ru>
To: Etsuro Fujita <etsuro.fujita@gmail.com>, Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Cc: Justin Pryzby <pryzby@telsasoft.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2021-04-26T10:35:53Z
Lists: pgsql-hackers

Attachments

On 4/23/21 8:12 AM, Etsuro Fujita wrote:
> I have committed the patch.
Small mistake i found. If no tuple was received from a foreign 
partition, explain shows that we never executed node. For example,
if we have 0 tuples in f1 and 100 tuples in f2:

Query:
EXPLAIN (ANALYZE, VERBOSE, TIMING OFF, COSTS OFF)
SELECT * FROM (SELECT * FROM f1 UNION ALL SELECT * FROM f2) AS q1
LIMIT 101;

Explain:
  Limit (actual rows=100 loops=1)
    Output: f1.a
    ->  Append (actual rows=100 loops=1)
          ->  Async Foreign Scan on public.f1 (never executed)
                Output: f1.a
                Remote SQL: SELECT a FROM public.l1
          ->  Async Foreign Scan on public.f2 (actual rows=100 loops=1)
                Output: f2.a
                Remote SQL: SELECT a FROM public.l2

The patch in the attachment fixes this.

-- 
regards,
Andrey Lepikhov
Postgres Professional

Commits

  1. Improve comments for trivial_subqueryscan().

  2. Disable asynchronous execution if using gating Result nodes.

  3. Allow asynchronous execution in more cases.

  4. Doc: Further update documentation for asynchronous execution.

  5. Fix rescanning of async-aware Append nodes.

  6. Doc: Update documentation for asynchronous execution.

  7. Fix EXPLAIN ANALYZE for async-capable nodes.

  8. Minor code cleanup in asynchronous execution support.

  9. Adjust input value to WaitEventSetWait() in ExecAppendAsyncEventWait().

  10. Add support for asynchronous execution.