Session variables and C functions
I'm writing a custom C function and one of the things it needs to do is
to be configured from the SQL-land, per user session (different users
have different configurations in different sessions).
I have found (and have used) the SET SESSION command and the
current_setting() function for use with custom_variable_classes
configuration in postgresql.conf, but I'm not sure how to achieve the
same effect from C.
Ideally, the C module would create its own "custom variable class,"
named e.g. "module", then define some setting, e.g. "module.setting".
The users would then execute an SQL command such as "SET SESSION
module.setting='something'", and the module would need to pick this up
in the C function.
Any pointers to how this would be done?
Ivan Voras <ivoras@freebsd.org> writes:
Ideally, the C module would create its own "custom variable class,"
named e.g. "module", then define some setting, e.g. "module.setting".
The users would then execute an SQL command such as "SET SESSION
module.setting='something'", and the module would need to pick this up
in the C function.
Plenty of examples of that in contrib/ ...
regards, tom lane
On 17 November 2011 19:02, Tom Lane <tgl@sss.pgh.pa.us> wrote:
Ivan Voras <ivoras@freebsd.org> writes:
Ideally, the C module would create its own "custom variable class,"
named e.g. "module", then define some setting, e.g. "module.setting".
The users would then execute an SQL command such as "SET SESSION
module.setting='something'", and the module would need to pick this up
in the C function.Plenty of examples of that in contrib/ ...
Ok, I found DefineCustom*() and _PG_init() but there's a small
problem: the functions I'm writing are for a user defined typed and
apparently _PG_init() is not called until some operation with the type
is done (e.g. anything with the input/output functions).
This means that DefineCustom*() is not called and PG doesn't know
about the variable until it's too late - I need the session variable
to be settable by the user before input/output - relying on the
"default value" is not enough.
Is there any way to make _PG_init() called earlier, e.g. as soon as
the session is established or at database connection time, something
like that?
Ivan Voras <ivoras@freebsd.org> writes:
Is there any way to make _PG_init() called earlier, e.g. as soon as
the session is established or at database connection time, something
like that?
Preload the library --- see shared/local_preload_libraries configuration
settings.
regards, tom lane
On 18 November 2011 01:20, Tom Lane <tgl@sss.pgh.pa.us> wrote:
Ivan Voras <ivoras@freebsd.org> writes:
Is there any way to make _PG_init() called earlier, e.g. as soon as
the session is established or at database connection time, something
like that?Preload the library --- see shared/local_preload_libraries configuration
settings.
Ok, thanks!