Thread

1. Trigger functions and parallelism

   Karl O. Pinc <kop@karlpinc.com> — 2023-10-02T16:49:42Z

   Hi,
   
   It's not entirely clear to me what the conditions
   are for function parallel safety.  While the documentation
   seems pretty clear in most cases, there still some
   verbiage that requires knowledge of internals
   in order to be useful.
   
   What I'm looking for is some general statements about
   parallel safety for trigger functions.  I don't know
   enough about parallelism to even know if it applies
   to data modification statements.
   
   It seems to me that, because raising any sort of exception
   affects transaction state, that triggers which 
   validate data integrity and raise errors must be PARALLEL UNSAFE.
   
   But are any sort of AFTER INSERT trigger on a generated sequential key
   parallel UNSAFE because they access sequence state via NEW?
   
   Can something generic be said, like: "Most trigger functions should
   be declared PARALLEL UNSAFE (the default) with the possible exception
   of BEFORE triggers that raise no exceptions and control system
   behavior by their return value."?  
   
   What can be said to provide some overview which gives
   guidance on parallelism to trigger authors?
   
   Regards,
   
   Karl <kop@karlpinc.com>
   Free Software:  "You don't pay back, you pay forward."
                    -- Robert A. Heinlein
   
   
   
   

2. Re: Trigger functions and parallelism

   Tom Lane <tgl@sss.pgh.pa.us> — 2023-10-02T17:07:19Z

   "Karl O. Pinc" <kop@karlpinc.com> writes:
   > What I'm looking for is some general statements about
   > parallel safety for trigger functions.  I don't know
   > enough about parallelism to even know if it applies
   > to data modification statements.
   
   It doesn't, which is why the docs are silent on the point.
   
   			regards, tom lane
   
   
   
   

3. Re: Trigger functions and parallelism

   Karl O. Pinc <kop@karlpinc.com> — 2023-10-02T19:23:00Z

   On Mon, 02 Oct 2023 13:07:19 -0400
   Tom Lane <tgl@sss.pgh.pa.us> wrote:
   
   > "Karl O. Pinc" <kop@karlpinc.com> writes:
   > > What I'm looking for is some general statements about
   > > parallel safety for trigger functions.  I don't know
   > > enough about parallelism to even know if it applies
   > > to data modification statements.  
   > 
   > It doesn't, which is why the docs are silent on the point.
   
   Thanks.
   
   Regards,
   
   Karl <kop@karlpinc.com>
   Free Software:  "You don't pay back, you pay forward."
                    -- Robert A. Heinlein