Fix create for libpq 9.6 and older db

[omergertel]

When Postgres library (libpq) 9.6 is installed on the server, pg_dump adds an SQL command to SET idle_in_transaction_session_timeout, which is new to 9.6, so it fails when running against older versions of the Postgres database.

I've added the parameter to the blacklist.

Is this acceptable?

[caironoleto]

These changes break in rails 5. Can you look?

[omergertel]

There are other PRs with unrelated changes that fail on the same tests, so I don't think the problems are caused by my changes. If I have a chance to investigate further, I'll try and help.

[meganemura]

The reason which breaks Rails 5.0 tests is solved in #449.
rebase to the current development branch would make the build success.

[mikecmpbll]

i don't really know much about pg. @meganemura — does this seem okay to you? if so, i'll merge :).

[meganemura]

@mikecmpbll

I actually don't know much about pg either.

Those statements in black list are ignored from dumped schema on cloning pg schema.
I think idle_in_transaction_session_timeout is not important for cloning only schema.
So, it looks good to me.

[mikecmpbll]

@meganemura whups, my bad, thought you were a pg user :)

@omergertel why would you ever be dumping with 9.6 and loading the dump into an older version?

[omergertel]

Not quite what happens.

This blocks the tenant creation if the client (libqp) is in version 9.6 and the database server is in version 9.5, because the client library adds the SET idle_in_transaction_session_timeout to the dump on its own.
The dump and restore are actually to the same database.

In our case, we've found out that Heroku have updated the client library to 9.6 in all of their images, and we were still running the database on 9.5. That's mostly ok because libpq is mostly backwards compatible. Except for this one setting.

Generally, it isn't farfetched to have a server running a client library different than the version of the database (as database upgrades are much more difficult and less frequent than, say, running apt-get on your machine).

This is the same reasoning behind the 9.3 workaround already in the code, I think.

[mikecmpbll]

the essence of the issue then is using incompatible versions of the client and server libraries :/. not sure why we'd do anything about that in apartment but seeing as, as you correctly pointed out, we already are, i'll merge..

[omergertel]

Thank you!