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