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diff --git a/doc/development/profiling.md b/doc/development/profiling.md index 76c89d361fc..ce9c1191648 100644 --- a/doc/development/profiling.md +++ b/doc/development/profiling.md @@ -128,8 +128,66 @@ console. As a follow up to finding `N+1` queries with Bullet, consider writing a [QueryRecoder test](query_recorder.md) to prevent a regression. +## System stats + +During or after profiling, you may want to get detailed information about the Ruby virtual machine process, +such as memory consumption, time spent on CPU, or garbage collector statistics. These are easy to produce individually +through various tools, but for convenience, a summary endpoint has been added that exports this data as a JSON payload: + +```shell +curl localhost:3000/-/metrics/system | jq +``` + +Example output: + +```json +{ + "version": "ruby 2.7.2p137 (2020-10-01 revision a8323b79eb) [x86_64-linux-gnu]", + "gc_stat": { + "count": 118, + "heap_allocated_pages": 11503, + "heap_sorted_length": 11503, + "heap_allocatable_pages": 0, + "heap_available_slots": 4688580, + "heap_live_slots": 3451712, + "heap_free_slots": 1236868, + "heap_final_slots": 0, + "heap_marked_slots": 3451450, + "heap_eden_pages": 11503, + "heap_tomb_pages": 0, + "total_allocated_pages": 11503, + "total_freed_pages": 0, + "total_allocated_objects": 32679478, + "total_freed_objects": 29227766, + "malloc_increase_bytes": 84760, + "malloc_increase_bytes_limit": 32883343, + "minor_gc_count": 88, + "major_gc_count": 30, + "compact_count": 0, + "remembered_wb_unprotected_objects": 114228, + "remembered_wb_unprotected_objects_limit": 228456, + "old_objects": 3185330, + "old_objects_limit": 6370660, + "oldmalloc_increase_bytes": 21838024, + "oldmalloc_increase_bytes_limit": 119181499 + }, + "memory_rss": 1326501888, + "memory_uss": 1048563712, + "memory_pss": 1139554304, + "time_cputime": 82.885264633, + "time_realtime": 1610459445.5579069, + "time_monotonic": 24001.23145713, + "worker_id": "puma_0" +} +``` + +NOTE: +This endpoint is only available for Rails web workers. Sidekiq workers can not be inspected this way. + ## Settings that impact performance +### Application settings + 1. `development` environment by default works with hot-reloading enabled, this makes Rails to check file changes every request, and create a potential contention lock, as hot reload is single threaded. 1. `development` environment can load code lazily once the request is fired which results in first request to always be slow. @@ -140,3 +198,34 @@ To disable those features for profiling/benchmarking set the `RAILS_PROFILE` env - restart GDK with `gdk restart` *This environment variable is only applicable for the development mode.* + +### GC settings + +Ruby's garbage collector (GC) can be tuned via a variety of environment variables that will directly impact application performance. + +The following table lists these variables along with their default values. + +| Environment variable | Default value | +|--|--| +| `RUBY_GC_HEAP_INIT_SLOTS` | `10000` | +| `RUBY_GC_HEAP_FREE_SLOTS` | `4096` | +| `RUBY_GC_HEAP_FREE_SLOTS_MIN_RATIO` | `0.20` | +| `RUBY_GC_HEAP_FREE_SLOTS_GOAL_RATIO` | `0.40` | +| `RUBY_GC_HEAP_FREE_SLOTS_MAX_RATIO` | `0.65` | +| `RUBY_GC_HEAP_GROWTH_FACTOR` | `1.8` | +| `RUBY_GC_HEAP_GROWTH_MAX_SLOTS` | `0 (disable)` | +| `RUBY_GC_HEAP_OLDOBJECT_LIMIT_FACTOR` | `2.0` | +| `RUBY_GC_MALLOC_LIMIT(_MIN)` | `(16 * 1024 * 1024 /* 16MB */)` | +| `RUBY_GC_MALLOC_LIMIT_MAX` | `(32 * 1024 * 1024 /* 32MB */)` | +| `RUBY_GC_MALLOC_LIMIT_GROWTH_FACTOR` | `1.4` | +| `RUBY_GC_OLDMALLOC_LIMIT(_MIN)` | `(16 * 1024 * 1024 /* 16MB */)` | +| `RUBY_GC_OLDMALLOC_LIMIT_MAX` | `(128 * 1024 * 1024 /* 128MB */)` | +| `RUBY_GC_OLDMALLOC_LIMIT_GROWTH_FACTOR` | `1.2` | + +([Source](https://github.com/ruby/ruby/blob/45b29754cfba8435bc4980a87cd0d32c648f8a2e/gc.c#L254-L308)) + +GitLab may decide to change these settings in order to speed up application performance, lower memory requirements, or both. + +You can see how each of these settings affect GC performance, memory use and application start-up time for an idle instance of +GitLab by runnning the `scripts/perf/gc/collect_gc_stats.rb` script. It will output GC stats and general timing data to standard +out as CSV. |