As of 1f68726cb8, the upgrade-postgresql tool uses Python to connect
to the database used by Django, and thus requires a working venv.
There is no reason we cannot reinstall the venv with the old version
of PostgreSQL; swap the steps.
Updates all the https://chat.zulip.org/#narrow/stream/ links in the
docs and comments to use the new /channel/ path. All these links are
for documentation/reference purposes only and thus, can be bulk-updated.
This commit is a part of the effort to rename stream to channel.
Users can, quite understandably, assume that upgrading Zulip upgraded
the underlying PostgreSQL version. Though it is mentioned at the top
of the page, mentioning it here clarifies that it is an additional
step.
Instead of copying over a mostly-unchanged `postgresql.conf`, we
transition to deploying a `conf.d/zulip.conf` which contains the
only material changes we made to the file, which were previously
appended to the end.
While shipping separate while `postgresql.conf` files for each
supported version is useful if there is large variety in supported
options between versions, there is not no such variation at current,
and the burden of overriding the entire default configuration is that
it must be keep up to date wit the package's version.
These hooks are run immediately around the critical section of the
upgrade. If the upgrade fails for preparatory reasons, the pre-deploy
hook may not be run; if it fails during the upgrade, the post-deploy
hook will not be run. Hooks are called from the CWD of the new
deploy, with arguments of the old version and the new version. If
they exit with non-0 exit code, the deploy aborts.
