Thread: in C trigger function find out if column is part of primary key
Hello C-(trigger)-experts,
I have to find out if a column ( i = 0, …, tupdesc->natts-1 ) is part of a primary key
but for performance reasons I do not want to execute another query via SPI.
Is this possible?
Currently I did not find a way, instead I check for “not null” attribute tupdesc->attrs[i]->attnotnull
and in addition if the column is used in an index via relation->rd_indexattr
but this Bitmapset has 8 leading zeros.
Is there a define which I can use instead of hardcode the 8? Currently I use bms_is_member(i + 8, rd_indexattr)
Thank you,
Michael
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On Mon, Apr 01, 2013 at 12:06:25AM +0200, Enke, Dr., Michael wrote: > I have to find out if a column ( i = 0, ..., tupdesc->natts-1 ) is part of a primary key > but for performance reasons I do not want to execute another query via SPI. > Is this possible? Simpler and probably even faster approach would be to do catalog lookup via SPI and then cache the result. The trick here is to get cache invalidation right, so on any table change cache is refreshed. You can use PgQ triggers as example: https://github.com/markokr/skytools/blob/master/sql/pgq/triggers/common.c It implements various unrelated features, but basics are in find_table_info() which loads cached data and relcache_reset_cb() which invalidates. -- marko
"Enke, Dr., Michael" <michael.enke@wincor-nixdorf.com> wrote: > I have to find out if a column ( i = 0, …, tupdesc->natts-1 ) is > part of a primary key but for performance reasons I do not want > to execute another query via SPI. Is this possible? You might get some inspiration from looking at this bit of code: http://git.postgresql.org/gitweb/?p=postgresql.git;a=blob;f=contrib/tcn/tcn.c;h=eb7e1a61a6a1d5c5ed2e840af41410ac4a52418f;hb=master#l127 -- Kevin Grittner EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company