Getting my Database name in a C Extension

[Cedric Berger]

Hi,

I'm writing an extention (FDW), and I need, in my C code, the name of
my database ("contrib_regression_test" for example), and I've two
questions:

1) What is the easiest way to get that directly in C?

2) Is there a way to get this information in the SQL extension
installation/update scripts (like the @/extschema/@ substitution)?

Thanks,

Cedric

[Tom Lane]

Post by Cedric Berger
I'm writing an extention (FDW), and I need, in my C code, the name of
my database ("contrib_regression_test" for example), and I've two
1) What is the easiest way to get that directly in C?

The usual locution is "get_database_name(MyDatabaseId)".

Post by Cedric Berger
2) Is there a way to get this information in the SQL extension

Nope. Doesn't seem to me like a remarkably good idea to refer to it
in that sort of way anyway. What would happen if someone renamed
the database after the extension is installed?

regards, tom lane

[Cedric Berger]

Post by Tom Lane

Post by Cedric Berger
1) What is the easiest way to get that directly in C?

The usual locution is "get_database_name(MyDatabaseId)".

Ok, but then how do I find "MyDatabaseId" in, say,
a BeginForeignScan() or GetForeignRelSize() FDW callback?

http://www.postgresql.org/docs/9.3/static/fdw-callbacks.html

Sorry for these beginner's questions, but I've trouble navigating
the documentation / source / examples for this kind of info.

PS: is "which see for additional details" really good English
in the fdw-callbacks.html documentation?

Post by Tom Lane

Post by Cedric Berger
2) Is there a way to get this information in the SQL extension

Nope. Doesn't seem to me like a remarkably good idea to refer to it
in that sort of way anyway. What would happen if someone renamed
the database after the extension is installed?

Ok,
Make sense,

Thanks
Cedric

[Albe Laurenz]

Post by Cedric Berger

Post by Tom Lane

Post by Cedric Berger
1) What is the easiest way to get that directly in C?

The usual locution is "get_database_name(MyDatabaseId)".

Ok, but then how do I find "MyDatabaseId" in, say,
a BeginForeignScan() or GetForeignRelSize() FDW callback?

It is a global, all you should have to do is
#include "miscadmin.h"

Yours,
Laurenz Albe

[Michael Paquier]

Post by Albe Laurenz

Post by Cedric Berger

Post by Tom Lane

Post by Cedric Berger
1) What is the easiest way to get that directly in C?

The usual locution is "get_database_name(MyDatabaseId)".

Ok, but then how do I find "MyDatabaseId" in, say,
a BeginForeignScan() or GetForeignRelSize() FDW callback?

It is a global, all you should have to do is
#include "miscadmin.h"

When looking for a global variable, a command like that is generally useful:
$ git grep MyDatabaseId -- *.h
src/include/access/xact.h: Oid dbId;
/* MyDatabaseId */
src/include/miscadmin.h:extern PGDLLIMPORT Oid MyDatabaseId;
Regards,

[Cedric Berger]

Post by Michael Paquier

Post by Albe Laurenz

Post by Cedric Berger

Post by Tom Lane

Post by Cedric Berger
1) What is the easiest way to get that directly in C?

The usual locution is "get_database_name(MyDatabaseId)".

Ok, but then how do I find "MyDatabaseId" in, say,
a BeginForeignScan() or GetForeignRelSize() FDW callback?

It is a global, all you should have to do is
#include "miscadmin.h"

$ git grep MyDatabaseId -- *.h
src/include/access/xact.h: Oid dbId;
/* MyDatabaseId */
src/include/miscadmin.h:extern PGDLLIMPORT Oid MyDatabaseId;

Thanks a lot!

I didn't think 'MyDatabaseId' was a real variable name...

Cedric

[Cedric Berger]

Hi,

I'm writing an extention (FDW), and I need, in my C code, the name of
my database ("contrib_regression_test" for example), and I've two
questions:

1) What is the easiest way to get that directly in C?

2) Is there a way to get this information in the SQL extension
installation/update scripts (like the @/extschema/@ substitution)?

Thanks,
--
Cedric Berger
Precidata Sarl
Maladière 71c
2000 Neuchâtel
***@precidata.com
032 930 29 62
079 934 11 02

[John R Pierce]

Post by Cedric Berger
I'm writing an extention (FDW), and I need, in my C code, the name of
my database ("contrib_regression_test" for example), and I've two
1) What is the easiest way to get that directly in C?
2) Is there a way to get this information in the SQL extension

you could SELECT CURRENT_CATALOG; using the SPI_ functions from your C,
or directly in your SQL extension script... this returns the database
name (the name is from the sql standard). see
http://www.postgresql.org/docs/current/static/functions-info.html for
more info functions like this available in SQL.