Thread

1. How to prohibit parallel scan through tableam?

   Konstantin Knizhnik <k.knizhnik@postgrespro.ru> — 2019-11-27T11:33:42Z

   Hi hackers,
   
   I wonder how it is possible to prohibit parallel scan for the external 
   storage accessed through tableam?
   For example if I want to implement specialized tableam for fast access 
   to temp tables, how can I inform optimizer that
   parallel scan is not possible (because table data is local to the backend)?
   
   Thanks in advance,
   
   -- 
   Konstantin Knizhnik
   Postgres Professional: http://www.postgrespro.com
   The Russian Postgres Company
   
   
   
   
   

2. Re: How to prohibit parallel scan through tableam?

   Rafia Sabih <rafia.pghackers@gmail.com> — 2019-11-27T12:12:35Z

   On Wed, 27 Nov 2019 at 12:33, Konstantin Knizhnik <k.knizhnik@postgrespro.ru>
   wrote:
   
   > Hi hackers,
   >
   > I wonder how it is possible to prohibit parallel scan for the external
   > storage accessed through tableam?
   > For example if I want to implement specialized tableam for fast access
   > to temp tables, how can I inform optimizer that
   > parallel scan is not possible (because table data is local to the backend)?
   >
   >  How about setting parallel_setup_cost to disable_cost in costsize.c for
   your specific scan method.
   
   -- 
   Regards,
   Rafia Sabih
   

3. Re: How to prohibit parallel scan through tableam?

   Konstantin Knizhnik <k.knizhnik@postgrespro.ru> — 2019-11-27T13:10:20Z

   
   On 27.11.2019 15:12, Rafia Sabih wrote:
   >
   >
   > On Wed, 27 Nov 2019 at 12:33, Konstantin Knizhnik 
   > <k.knizhnik@postgrespro.ru <mailto:k.knizhnik@postgrespro.ru>> wrote:
   >
   >     Hi hackers,
   >
   >     I wonder how it is possible to prohibit parallel scan for the
   >     external
   >     storage accessed through tableam?
   >     For example if I want to implement specialized tableam for fast
   >     access
   >     to temp tables, how can I inform optimizer that
   >     parallel scan is not possible (because table data is local to the
   >     backend)?
   >
   >  How about setting parallel_setup_cost to disable_cost in costsize.c 
   > for your specific scan method.
   
   How can I do it if i just implementing my AM and not going to change any 
   postgres code?
   
   -- 
   Konstantin Knizhnik
   Postgres Professional: http://www.postgrespro.com
   The Russian Postgres Company
   
   

4. Re: How to prohibit parallel scan through tableam?

   Rafia Sabih <rafia.pghackers@gmail.com> — 2019-11-28T13:23:21Z

   On Wed, 27 Nov 2019 at 12:33, Konstantin Knizhnik <k.knizhnik@postgrespro.ru>
   wrote:
   
   > Hi hackers,
   >
   > I wonder how it is possible to prohibit parallel scan for the external
   > storage accessed through tableam?
   > For example if I want to implement specialized tableam for fast access
   > to temp tables, how can I inform optimizer that
   > parallel scan is not possible (because table data is local to the backend)?
   >
   > One moment, isn't that parallel scans are already restricted for temp
   tables, or I have misunderstood something here...?
   
   
   
   -- 
   Regards,
   Rafia Sabih
   

5. Re: How to prohibit parallel scan through tableam?

   Andres Freund <andres@anarazel.de> — 2019-12-03T21:22:17Z

   Hi,
   
   On 2019-11-27 14:33:42 +0300, Konstantin Knizhnik wrote:
   > I wonder how it is possible to prohibit parallel scan for the external
   > storage accessed through tableam?
   > For example if I want to implement specialized tableam for fast access to
   > temp tables, how can I inform optimizer that
   > parallel scan is not possible (because table data is local to the backend)?
   
   I don't think there currently is a good way to do so - but it shouldn't
   be hard to add that capability.
   
   Greetings,
   
   Andres Freund
   
   
   
   

6. Re: How to prohibit parallel scan through tableam?

   Andres Freund <andres@anarazel.de> — 2019-12-03T21:24:14Z

   Hi,
   
   On 2019-11-27 16:10:20 +0300, Konstantin Knizhnik wrote:
   > On 27.11.2019 15:12, Rafia Sabih wrote:
   > > On Wed, 27 Nov 2019 at 12:33, Konstantin Knizhnik
   > > <k.knizhnik@postgrespro.ru <mailto:k.knizhnik@postgrespro.ru>> wrote:
   > > 
   > >     Hi hackers,
   > > 
   > >     I wonder how it is possible to prohibit parallel scan for the
   > >     external
   > >     storage accessed through tableam?
   > >     For example if I want to implement specialized tableam for fast
   > >     access
   > >     to temp tables, how can I inform optimizer that
   > >     parallel scan is not possible (because table data is local to the
   > >     backend)?
   > > 
   > >  How about setting parallel_setup_cost to disable_cost in costsize.c for
   > > your specific scan method.
   > 
   > How can I do it if i just implementing my AM and not going to change any
   > postgres code?
   
   I think a set_rel_pathlist hook that prevents parallel paths from being
   considered would be your best bet for now. But I encourage you to
   suggest a patch to tableam to support it properly in future releases.
   
   Greetings,
   
   Andres Freund