On 2021/08/05 12:18, kuroda.hay...@fujitsu.com wrote:
Dear Hackers, Tom,
(I changed subject because this is no longer postgres_fdw's patch)
What would be better to think about is how to let users specify this
kind of behavior for themselves. I think it's possible to set
application_name as part of a foreign server's connection options,
but at present the result would only be a constant string. Somebody
who wished the PID to be in there would like to have some sort of
formatting escape, say "%p" for PID. Extrapolating wildly, maybe we
could make all the %-codes known to log_line_prefix available here.
I think your argument is better than mine. I will try to implement this
approach.
I made a patch based on your advice. I add parse and rewrite function in
connectOptions2().
I implemented in libpq layer, hence any other application can be used.
Here is an example:
```
$ env PGAPPNAME=000%p%utest000 psql -d postgres -c "show application_name"
application_name
-----------------------
00025632hayatotest000
(1 row)
```
Why did you make even %u and %d available in application_name?
With the patch, they are replaced with the user name to connect as
and the database name to connect to, respectively. Unlike %p
(i.e., PID in *client* side), those information can be easily viewed via
log_line_prefix and pg_stat_activity, etc in the server side.
So I'm not sure how much helpful to expose them also in application_name.
I don't think this is a great idea as-is. People who need to do this
sort of thing will all have their own ideas of what they need to track
--- most obviously, it might be appropriate to include the originating
server's name, else you don't know what machine the PID is for.
So some people may want to specify their own ID in application_name
when connecting to the foreign server. For now they can do that by
setting application_name per foreign server object. But this means that
every session connecting to the same foreign server basically should
use the same application_name. If they want to change the setting,
they need to execute "ALTER SERAVER ... OPTIONS ...". Isn't this inconvenient?
If yes, what about allowing us to specify foreign server's application_name
per session? For example, we can add postgres_fdw.application_name GUC,
and then if it's set postgres_fdw always uses it instead of the server-level
option when connecting to the foreign server. Thought?
Regards,
--
Fujii Masao
Advanced Computing Technology Center
Research and Development Headquarters
NTT DATA CORPORATION
