| From: | Simon Riggs <simon(at)2ndquadrant(dot)com> |
|---|---|
| To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
| Cc: | Craig Ringer <craig(at)2ndquadrant(dot)com>, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: [HACKERS] PATCH: enabling parallel execution for cursors explicitly (experimental) |
| Date: | 2018-01-17 13:58:45 |
| Message-ID: | CANP8+jJBHDu+kgH2Jy34zzx9C5x61LF7JkWODPaRKuXMhD0vKw@mail.gmail.com |
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| Lists: | pgsql-hackers |
On 2 November 2017 at 01:55, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> On Wed, Nov 1, 2017 at 7:49 AM, Craig Ringer <craig(at)2ndquadrant(dot)com> wrote:
>> If the client wants to fetch in chunks it can use a portal and limited
>> size fetches. That shouldn't (?) be parallel-unsafe, since nothing
>> else can happen in the middle anyway.
>
> I believe sending a limited-size fetch forces serial execution
> currently. If it's true that nothing else can happen in the middle
> then we could relax that, but I don't see why that should be true?
Perhaps the question is not "why" but "when"?
If a parallel cursor is requested, we could simply prevent other
intermediate commands other than FETCH (next).
--
Simon Riggs http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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