Move some common database import subroutines to Script::Utils

[mwiencek]

Problem

• We have some identical or very similar-looking subroutines duplicated between admin/MBImport.pl and admin/replication/ImportReplicationChanges: empty (to tell if a table is empty) and ImportTable (to import a table from a file). The two implementations of the latter function differ slightly.

• For the incremental dumps (MusicBrainz::Script::Role::IncrementalDump), I'd like to reuse the ImportTable function to import a dbmirror2 packet into some temporary tables (to parse it).

  We currently parse the old packets by hand; I'm surprised it works at all (it probably doesn't in some cases) because I don't believe it fully or properly implement's parsing of PostgreSQL's COPY text format. dbmirror2 packets contain JSON, which may contain JSON escape sequences underneath COPY's text format escape sequences, and the mixing of these can be tricky to parse. It's much, much easier to let PostgreSQL do the parsing!

Solution

This just adds two shared subroutines, is_table_empty and copy_table_from_file to Script::Utils, and modifies admin/MBImport.pl and admin/replication/ImportReplicationChanges to use them.

Testing

We have existing automated tests that make heavy use of these scripts.

I did not test the --fix-broken-utf8 or --ignore-errors flags specifically.

[reosarevok]

This seems sensible to me, but I'd prefer if we had a test for the extra flags if they wouldn't be too complex. Although it does kinda feel maybe we can just drop the utf8 flag, but maybe we should check with @mayhem first if he remembers the reasons. The comment mentioning automodsaccepted which I have never even seen suggests that this is ancient and the extra options might be unneeded.

[mwiencek]

This seems sensible to me, but I'd prefer if we had a test for the extra flags if they wouldn't be too complex. Although it does kinda feel maybe we can just drop the utf8 flag, but maybe we should check with @mayhem first if he remembers the reasons. The comment mentioning automodsaccepted which I have never even seen suggests that this is ancient and the extra options might be unneeded.

Well, I'm not sure how to test those easily (I guess I'd have to construct, by hand, some broken dumps with artificial errors?), but I didn't change how they work either. If I somehow broke them, it'd only be by passing the options incorrectly (via ignore_errors => $fIgnoreErrors, etc.).

I've never used these flags in all my time at MB, as far as I can remember. At the same time, I left them alone in the PR to avoid having to make a decision about removing them. :) Since it's unrelated to what I wanted to achieve here, which is making ImportTable reusable.

(Removing the draft status since this was finished when I submitted it.)