Re: Optimization for updating foreign tables in Postgres FDW

From: Etsuro Fujita <fujita(dot)etsuro(at)lab(dot)ntt(dot)co(dot)jp>
To: Michael Paquier <michael(dot)paquier(at)gmail(dot)com>, Noah Misch <noah(at)leadboat(dot)com>
Cc: Robert Haas <robertmhaas(at)gmail(dot)com>, Rushabh Lathia <rushabh(dot)lathia(at)gmail(dot)com>, Thom Brown <thom(at)linux(dot)com>, Stephen Frost <sfrost(at)snowman(dot)net>, Albe Laurenz <laurenz(dot)albe(at)wien(dot)gv(dot)at>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Shigeru Hanada <shigeru(dot)hanada(at)gmail(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Optimization for updating foreign tables in Postgres FDW
Date: 2016-04-19 04:14:02
Message-ID: 5715B08A.2030404@lab.ntt.co.jp
Views: Raw Message | Whole Thread | Download mbox
Thread:
Lists: pgsql-hackers

On 2016/04/19 12:45, Etsuro Fujita wrote:
> On 2016/04/19 12:26, Michael Paquier wrote:
>> Note for Robert: pgfdw_get_result copycats PQexec by discarding all
>> PQresult received except the last one. I think that's fine for the
>> purposes of postgres_fdw, but perhaps you have a different opinion on
>> the matter.

> That seemed reasonable to me, but sorry, on second thought, I'm not sure
> that's still a good idea. One reason is (1) I think it's better for the
> in-postgres_fdw.c functions using pgfdw_get_result to verify that there
> are no more results, in itself. I think that would improve the
> robustness of those functions. Another reason is I don't think
> pgfdw_report_error, which is used in pgfdw_get_result, works well for
> cases where the query contains multiple SQL commands. So, +1 for the
> idea of simply encapsulating the while (PQisBusy(...)) loop into a new
> function pgfdw_get_result().

Here is a proposed patch for that.

Other changes:

* We don't use a PG_TRY block here, so be careful not to throw error
* without releasing the PGresult.
*/
- res = PQexecPrepared(fmstate->conn,
- fmstate->p_name,
- fmstate->p_nums,
- p_values,
- NULL,
- NULL,
- 0);
+ if (!PQsendQueryPrepared(fmstate->conn,
+ fmstate->p_name,
+ fmstate->p_nums,
+ p_values,
+ NULL,
+ NULL,
+ 0))
+ pgfdw_report_error(ERROR, NULL, fmstate->conn, true, fmstate->query);

The comment "We don't use a PG_TRY block here ..." seems to be wrongly
placed, so I moved that comment. Also, I think it'd be better to call
pgfdw_report_error() with the clear argument set to false, not true,
since we don't need to clear the PGresult. Same for
postgresExecForeignUpdate, postgresExecForeignUpdate, and
prepare_foreign_modify.

What do you think about that?

Best regards,
Etsuro Fujita

Attachment Content-Type Size
pgfdw-interrupt-efujita.patch text/x-patch 21.8 KB

In response to

Responses

Browse pgsql-hackers by date

  From Date Subject
Next Message Noah Misch 2016-04-19 04:16:31 Re: [COMMITTERS] pgsql: Add trigonometric functions that work in degrees.
Previous Message Tom Lane 2016-04-19 03:56:55 Re: [COMMITTERS] pgsql: Add trigonometric functions that work in degrees.