Re: Using timestamp(tz) in C functions

On 07/28/2016 02:15 PM, Keith Fiske wrote:
> Working on trying to get a C version of the maintenance function for my
> pg_partman extension working so I can hopefully make it more flexible
> and efficient.
>
> https://github.com/keithf4/pg_partman/blob/master/sql/functions/run_maintenance.sql
>
> Up until this point I've just been using SPI and the Datum conversion
> functions (DatumGetCString, DatumGetInt32) to get string and numeric
> data out of tables and things have been working fine. I'm at the first
> point in that function where I'll need to start dealing with timestamp data.
>
> https://gist.github.com/keithf4/81c32bf8b689c74b20c10ad8c91d45a3#file-pg_partman_bgw-c-L532
>
> There's what I've got working so far and links directly to the area
> where I'm having a problem. I found the DatumGetTimeTzADTP() function
> and the TimeTzADT data type looking through the source and that seems to
> be exactly what I'm looking for. However, when I get to the point of
> trying to simply use the time value in that variable (line 544),
> Postgres segfaults. So far I've just been trying to print the value out
> to the log to ensure I'm pulling it out correctly. The "time" value of
> the struct appears to be an int64, so I thought %ld would be the
> correct, but even using %d or %s fails.
>
> You can see in my original plpgsql function how I eventually intend to
> use the timestamp values. Here's a link directly to the equivalent section
>
> https://github.com/keithf4/pg_partman/blob/master/sql/functions/run_maintenance.sql#L139
>
> So, not sure if I'm even going about this the right manner for the way I
> intend to use the timestamp values. Still fairly new to C and getting
> use to postgres internals. Any help, or even an example of using
> timstamp data pulled from a table in C with SPI, would be great.

https://www.postgresql.org/docs/current/static/contrib-spi.html


F.34.5. moddatetime — Functions for Tracking Last Modification Time

moddatetime() is a trigger that stores the current time into a timestamp
field. This can be useful for tracking the last modification time of a
particular row within a table.

To use, create a BEFORE UPDATE trigger using this function. Specify a
single trigger argument: the name of the column to be modified. The
column must be of type timestamp or timestamp with time zone.

There is an example in moddatetime.example.


Can be seen here:


https://git.postgresql.org/gitweb/?p=postgresql.git;a=blob;f=contrib/spi/moddatetime.c;h=c6d33b73557ff499faa0d475e032fd1f8164afbd;hb=HEAD
>
> Thanks!
>
> --
> Keith Fiske
> Database Administrator
> OmniTI Computer Consulting, Inc.
> http://www.keithf4.com


--
Adrian Klaver
adrian.klaver@aklaver.com