Re: multi-install PostgresNode fails with older postgres versions

On 4/7/21 10:37 AM, Jehan-Guillaume de Rorthais wrote:
> Hi all,
>
> First, sorry to step in this discussion this late. I didn't noticed it before :(
>
> I did some work about these compatibility issues in late 2020 to use
> PostgresNode in the check_pgactivity TAP tests.
>
> See https://github.com/ioguix/check_pgactivity/tree/tests/t/lib
>
> PostgresNode.pm, TestLib.pm, SimpleTee.pm and RecursiveCopy.pm comes unchanged
> from PostgreSQL source file (see headers and COPYRIGHT.pgsql).
>
> Then, I'm using the facet class PostgresNodeFacet to extend it with some more
> methods. Finaly, I created one class per majpr version, each inheriting from the
> next version. That means 13 inherits from PostgresNodeFacet.pm, 12 inherits from
> 13, 11 inherits from 12, etc.
>
> When I'm creating a new node, I'm using the "pgaTester" factory class. It
> relies on PATH to check the major version using pg_config, then loads the
> appropriate class.
>
> That means some class overrides almost no methods but version(), which returns
> the major version. Eg.:
> https://github.com/ioguix/check_pgactivity/blob/tests/t/lib/PostgresNode12.pm
>
> From tests, I can check the node version using this method, eg.:
>
> skip "skip non-compatible test on PostgreSQL 8.0 and before", 3
> unless $node->version <= 8.0;
>
> Of course, there's a lot of duplicate code between classes, but my main goal
> was to keep PostgresNode.pm unchanged from upstream so I can easily update it.
>
> And here is a demo test file:
> https://github.com/ioguix/check_pgactivity/blob/tests/t/01-streaming_delta.t
>
> My limited set of tests are working with versions back to 9.0 so far.
>
> My 2¢

I don't really want to create a multitude of classes. I think Mark is
basically on the right track. I started off using a subclass of
PostgresNode but was persuaded not to go down that route, and instead we
have made some fairly minimal changes to PostgresNode itself. I think
that was a good decision. If you take out the versioning subroutines,
the actual version-aware changes Mark is proposing to PostgresNode are
quite small - less that 200 lines supporting versions all the way back
to 8.1. That's pretty awesome.

cheers

andrew

--
Andrew Dunstan
EDB: https://www.enterprisedb.com