Re: multi-install PostgresNode fails with older postgres versions

> On Apr 3, 2021, at 11:01 AM, Andrew Dunstan <andrew(at)dunslane(dot)net> wrote:
>
> I've had a look at the first of these patches. I think it's generally
> ok, but:
>
>
> - TestLib::system_or_bail('initdb', '-D', $pgdata, '-A', 'trust', '-N',
> + TestLib::system_or_bail('initdb', '-D', $pgdata, '-A', 'trust',
> + $self->at_least_version("9.3") ? '-N' : (),
> @{ $params{extra} });
>
>
> I'd rather do this in two steps to make it clearer.

Changed.

> I still think just doing pg_ctl -w unconditionally would be simpler.

Changed.

> Prior to 9.3 "unix_socket_directories" was spelled
> "unix_socket_directory". We should just set a variable appropriately and
> use it. That should make the changes around that a whole lot simpler.
> (c.f. buildfarm code)

Ah, good to know. Changed.

Other changes:

The v1 patch supported postgres versions back to 8.4, but v2 pushes that back to 8.1.

The version of PostgresNode currently committed relies on IPC::Run in a way that is subtly wrong. The first time IPC::Run::run(X, ...) is called, it uses the PATH as it exists at that time, resolves the path for X, and caches it. Subsequent calls to IPC::Run::run(X, ...) use the cached path, without respecting changes to $ENV{PATH}. In practice, this means that:

use PostgresNode;

my $a = PostgresNode->get_new_node('a', install_path => '/my/install/8.4');
my $b = PostgresNode->get_new_node('b', install_path => '/my/install/9.0');

$a->safe_psql(...) # <=== Resolves and caches 'psql' as /my/install/8.4/bin/psql

$b->safe_psql(...) # <=== Executes /my/install/8.4/bin/psql, not /my/install/9.0/bin/psql as one might expect

PostgresNode::safe_psql() and PostgresNode::psql() both suffer from this, and similarly PostgresNode::pg_recvlogical_upto() because the path to pg_recvlogical gets cached. Calls to initdb and pg_ctl do not appear to suffer this problem, as they are ultimately handled by perl's system() call, not by IPC::Run::run.

Since postgres commands work fairly similarly from one release to another, this can cause subtle and hard to diagnose bugs in regression tests. The fix in v2-0001 works for me, as demonstrated by v2-0002, but whether the fix in the attached v2 patch set gets used or not, I think something needs to be done to fix this.