This can happen if `machine.pgroonga` is set during initial
installation. We cannot run `CREATE EXTENSION PGROONGA` because the
database that we need to run that statement in does not exist yet;
make the command a silent no-op that does not create the
`pgroonga_setup.sql.applied` flag file, such that a later
`zulip-puppet-apply` once the database exists can pick up and install
the extension.
Updating the pgroonga package is not sufficient to upgrade the
extension in PostgreSQL -- an `ALTER EXTENSION pgroonga UPDATE` must
explicitly be run[^1]. Failure to do so can lead to unexpected behavior,
including crashes of PostgreSQL.
Expand on the existing `pgroonga_setup.sql.applied` file, to track
which version of the PostgreSQL extension has been configured. If the
file exists but is empty, we run `ALTER EXTENSION pgroonga UPDATE`
regardless -- if it is a no-op, it still succeeds with a `NOTICE`:
```
zulip=# ALTER EXTENSION pgroonga UPDATE;
NOTICE: version "3.0.8" of extension "pgroonga" is already installed
ALTER EXTENSION
```
The simple `ALTER EXTENSION` is sufficient for the
backwards-compatible case[^1] -- which, for our usage, is every
upgrade since 0.9 -> 1.0. Since version 1.0 was released in 2015,
before pgroonga support was added to Zulip in 2016, we can assume for
the moment that all pgroonga upgrades are backwards-compatible, and
not bother regenerating indexes.
Fixes: #25989.
[^1]: https://pgroonga.github.io/upgrade/
Alex Vandiver