[RFC 0/2] Rework tagging infrastructure

[Stephen Finucane]

On Fri, 2018-03-16 at 15:38 +0100, vkabatov at redhat.com wrote:
> From: Veronika Kabatova <vkabatov at redhat.com>

I'm going to review this this week. However, this doesn't apply cleanly
to head of master any more (sorry :(). Any chance you could send
updated versions of these?

Stephen

> (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).
> 
> TL;DR:
> 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
>