[Meta] GitLab.com performance

• Successor to "GitLab.com Latency" #947 (closed) and "Back calculate gains needed" #1830 (closed).
• Action items are also to be listed on https://about.gitlab.com/handbook/engineering/performance

Analysis to be done

• Analyze transaction time and correlation with rails controller time #1877 (closed)
• Analyze reasons for performance difference on two issues, as case study #1880 (closed)

Monitoring to be added - included on handbook/engineering/performance

• Gather monitoring data for longer time periods #1879 (closed)
  • Enable Prometheus collection of InfluxDB metrics #1022 (closed)
• Allow more GitLab internals monitoring https://gitlab.com/gitlab-org/gitlab-ce/issues/28465
• Making workhorse timings available https://gitlab.com/gitlab-com/infrastructure/issues/2025

Tracking ongoing efforts - all listed on the engineering handbook page.

• [meta] Overview of top 10 slowest queries https://gitlab.com/gitlab-org/gitlab-ce/issues/34535
• [meta] Scoping work on completing the transition to Gitaly gitlab-org/gitaly#313 (closed)
• [meta] Frontend Performance Audit https://gitlab.com/gitlab-org/gitlab-ce/issues/33958
• Setting up CDN for GitLab.com #2092 (closed) (successor to #57 (closed) )
• Compressing html with gzip in nginx https://gitlab.com/gitlab-org/gitlab-ce/issues/33719
• Slow SSL Connection Establishment #2321 (closed)

\cc @gl-infra @sitschner @stanhu @sytses @bjk-gitlab