[RFC 0/2] Rework tagging infrastructure

vkabatov at redhat.com vkabatov at redhat.com
Sat Mar 17 01:38:30 AEDT 2018

From: Veronika Kabatova <vkabatov at redhat.com>

(TL;DR at the end)

This RFC describes an approach to rework tagging. It attempts to solve GitHub
issues #57 [1] and #113 [2] as well as some other things we encountered. I'm
sending the incomplete version (eg I haven't fixed the tests) to discuss the
approach first.

Right now, tags are extracted from all the comments on the patch and the patch
itself, and they are reextracted from all the sources every time a comment is
added or removed. It makes saving slower, and might contribute to races with
writes to database when we are parsing multiple emails at the same time. This
gets even more prevalent if we want to solve the issue #113 (tags on cover
letter should increment counters on every patch in series) -- for each added
comment on the cover letter, we would reextract tags from all the other sources,
for each patch in series; and for a change on comments related to the patch
directly, we would need to take the tags on the cover letter and it's comments
into account as well (I implemented this solution in my fork but I really
don't like it).

The current approach has several other issues as well, some of which are
mentioned in the issue #57, eg duplicate tags are counted more times. Taking
into account the tags on cover letters would also be easier if we could store
tags against them and just query them on demand, instead of reextracting
everything all over again.

Solutions for some other things we found missing solve the issues mentioned
above too. If we want to determine if the tag is duplicate, we need to save the
associated value. Having the value would help us to use arbitrary strings as
tags (for example links to issue trackers, like `Bugzilla: <link>` if the patch
solves a known bug). The key-values approach to storing tags is mentioned [3],
this email additionally mentions a currently nonexistent /comments REST API
which we would like to implement some time in the future. For the comments API
we would also find it very useful to have the tags extracted from the comments
available directly so we can query for them, which means we would either need to
reextract the tags on every API call, or we could store the tags against the
comments as they are extracted and only query them as needed. Keeping tags
related to comments where they originated from avoids the need to reextract
tags with addition of new comments, as well as gets rid of the `patch_responses`
property used when converting comments to mbox (we finally get all the custom
tags there instead of only the few hardcoded ones).

Our goals:
- Avoid tag reextraction with each added comment
- Fix issues #57 and #113
- Prepare things for addition of /comments API
- Add tags to patch (currently returns {}) and cover letter APIs

If you agree with the general idea, I'd like to get some help with DB query
optimizations. Tags are more distributed, so counting them in PatchQuerySet is
harder. I wanted to use annotation with Django's conditional selection, but it
doesn't seem to work very well and generated invalid SQL in my attempts (hence
my temporary solution with counting the tags on the fly only for the patches
that are being displayed). That said, I'm not a DB expert so any faster working
solutions are more than welcome.

Thoughts? Ideas?

[1] https://github.com/getpatchwork/patchwork/issues/57
[2] https://github.com/getpatchwork/patchwork/issues/113
[3] https://lists.ozlabs.org/pipermail/patchwork/2018-January/004741.html

Veronika Kabatova (2):
  Rework tagging infrastructure
  Add migration for tagging changes

 docs/deployment/management.rst              |  16 +--
 patchwork/api/cover.py                      |  32 ++++-
 patchwork/api/patch.py                      |  41 +++++-
 patchwork/management/commands/retag.py      |  14 +-
 patchwork/migrations/0024_rework_tagging.py | 137 ++++++++++++++++++
 patchwork/models.py                         | 210 ++++++++++++++--------------
 patchwork/templatetags/patch.py             |   3 +-
 patchwork/views/__init__.py                 |   3 -
 patchwork/views/utils.py                    |   8 +-
 9 files changed, 331 insertions(+), 133 deletions(-)
 create mode 100644 patchwork/migrations/0024_rework_tagging.py


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