Re: Proposal: Store "timestamptz" of database creation on "pg_database"

Stephen Frost <sfrost(at)snowman(dot)net> writes:
> Apparently I've managed to miss the tricky case..?

That shouldn't be tricky as a user, but has been a tricky subject every
time we've been talking about implement Event Triggers in the past two
years, so I though I would include it:

create schema test
create table foo(id serial primary key, f1 text);

create event trigger track_table
on ddl_command_trace
when tag in ('create table', 'alter table', 'drop table')
and context in ('toplevel', 'generated', 'subcommand')
execute procedure public.track_table_activity();

The trick is that you then want to fire the event trigger for a command
in a 'subcommand' context, as seen in the logs provided by the "snitch"
example:

NOTICE: snitch event: ddl_command_end, context: SUBCOMMAND
NOTICE: tag: CREATE TABLE, operation: CREATE, type: TABLE
NOTICE: oid: 25139, schema: test, name: foo

> Sure, dropping tables, schemas, etc, would have an impact on the values.

we don't have, as of yet, support for a 'cascade' context. We will need
some heavy refactoring to get there, basically forcing the cascade drops
to happen via ProcessUtility(), but having a single DropStmt to handle
that I guess it shouldn't be very hard to do.

> being told "oh, well, you *could* have been collecting it all along if
> you knew about event triggers" isn't a particularly satisfying answer.

True that.

Now, having at least a way to do that without resorting to hacking the
backend or writing a C coded extension sure feels nice enough an answer
to me here.

Regards,
--
Dimitri Fontaine
http://2ndQuadrant.fr PostgreSQL : Expertise, Formation et Support