This issue is to talk about optimising running configuration of GitLab Exporter. Specifically we will look at `jemalloc` and tune it, as well as Ruby GC specific settings. ### Final results All the improvements are merged. Here is a before-after comparison. Approach: using default settings for gitlab-exporter, boot a fresh Omnibus container and run `ab -c 2 -n 20 localhost:9168/metrics` which polls all available probes. This was running webrick. I then took memory measurements via `smem`. #### Omnibus 13.8.1-ee.0 ``` root@local:/# smem -P gitlab-exporter PID User Command Swap USS PSS RSS 725 git /opt/gitlab/embedded/bin/ru 0 106864 107404 116596 ``` #### Omnibus 13.9.202102010906-fda844058cc.738441f3bc2 (`jemalloc` tweaks only) ``` root@local:/# smem -P gitlab-exporter PID User Command Swap USS PSS RSS 4548 git /opt/gitlab/embedded/bin/ru 0 34376 34986 45248 ``` #### Omnibus 13.9.202102010906-fda844058cc.738441f3bc2 (`jemalloc` tweaks + `RUBY_GC_*` tweaks) The `RUBY_GC_*` settings were manually applied and are *not* defaults yet. ``` RUBY_GC_HEAP_INIT_SLOTS=80000 RUBY_GC_HEAP_FREE_SLOTS_MIN_RATIO=0.055 # 5k/90k RUBY_GC_HEAP_FREE_SLOTS_MAX_RATIO=0.111 # 10k/90k ``` ``` root@local:/# smem -P gitlab-exporter PID User Command Swap USS PSS RSS 1286 git /opt/gitlab/embedded/bin/ru 0 38056 38731 49120 ``` #### Result The improvement is anywhere between **57%-61% reduction in memory use (~67-71MB).** With GC tuning applied, memory use is slightly higher even, but could potentially be less spiky over time. I took a one-time measurement after the test suite finished. If we ship things "as is", then outcome 2 would apply, i.e. jemalloc is used, but Ruby GC would use defaults.