Optimize push-list endpoint

[vrigal]

Changes

• Related commits (revisions in the serializer) are now prefetched, but not limited to 20 results as before (django does not supports slicing a prefetch, but it is possible in SQL)
  • Avoids 1 SQL request per Push
  • 35516 / 1260041 Push entries are linked to more than 20 commits. 8 are linked to ~10k commits.

Performance

• Small data (/api/project/autoland/push/?full=true&count=100&fromchange=<rev_id>)

  • master : 569 ms ± 5.12 ms per loop (mean ± std. dev. of 7 runs, 1 loop each)
  • e6109c95: 520 ms ± 4.65 ms per loop (mean ± std. dev. of 7 runs, 1 loop each)
  • Approx 9% time reduction

• Large data (/api/project/autoland/push/?full=true&count=100)

  • master : 5.69 s ± 63.6 ms per loop (mean ± std. dev. of 7 runs, 1 loop each)
  • e6109c95: 1.87 s ± 69.5 ms per loop (mean ± std. dev. of 7 runs, 1 loop each)
  • Approx 66% time reduction

[codecov-commenter]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (b16dbb9) 76.84% compared to head (e6109c9) 76.84%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #7817      +/-   ##
==========================================
- Coverage   76.84%   76.84%   -0.01%     
==========================================
  Files         537      537              
  Lines       26556    26554       -2     
  Branches     3359     3359              
==========================================
- Hits        20408    20406       -2     
  Misses       5983     5983              
  Partials      165      165              

Files	Coverage Δ
tests/push_health/test_compare.py	100.00% <100.00%> (ø)
treeherder/push_health/usage.py	100.00% <100.00%> (ø)
treeherder/webapp/api/serializers.py	87.86% <100.00%> (-0.29%)	⬇️
treeherder/webapp/api/push.py	58.29% <80.00%> (+0.18%)	⬆️

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.