1. 05 Nov, 2018 1 commit
    • Yorick Peterse's avatar
      Rewrite SnippetsFinder to improve performance · b81102d2d9a4
      Yorick Peterse authored
      This completely rewrites the SnippetsFinder class from the ground up in
      order to improve its performance. The old code was beyond salvaging. It
      was complex, included various Rails 5 workarounds, comments that
      shouldn't be necessary, and most important of all: it produced a really
      poorly performing database query.
      
      As a result, I opted for rewriting the finder from scratch, instead of
      trying to patch the existing code. Instead of trying to reuse as many
      existing methods as possible, I opted for defining new methods
      specifically meant for the SnippetsFinder. This requires some extra code
      here and there, but allows us to have much more control over the
      resulting SQL queries. It is these changes that then allow us to produce
      a _much_ more efficient query.
      
      To illustrate how bad the old query was, we will use my own snippets as
      an example. Currently I have 52 snippets, most of which are global ones.
      To retrieve these, you would run the following Ruby code:
      
          user = User.find_by(username: 'yorickpeterse')
      
          SnippetsFinder.new(user, author: user).execute
      
      On GitLab.com the resulting query will take between 10 and 15 seconds to
      run, producing the query plan found at
      https://explain.depesz.com/s/Y5IX. Apart from the long execution time,
      the total number of buffers (the sum of all shared hits) is around 185
      GB, though the real number is probably (hopefully) much lower as I doubt
      simply summing these numbers produces the true total number of buffers
      used.
      
      The new query's plan can be found at https://explain.depesz.com/s/wHdN,
      and this query takes between 10 and 100-ish milliseconds to run. The
      total number of buffers used is only about 30 MB.
      
      Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/52639
      b81102d2d9a4
  2. 01 Nov, 2018 17 commits
  3. 31 Oct, 2018 22 commits