NXD Teach gitlab-workhorse to serve requests to get raw blobs
[ Sent upstream: https://gitlab.com/gitlab-org/gitlab-workhorse/merge_requests/17 This patch was sent upstream but was not accepted for "complexity" reason of auth cache (next patch), despite that provides more than an order of magnitude speedup. Just carry it with us as NXD ] Currently GitLab serves requests to get raw blobs via Ruby-on-Rails code and Unicorn. Because RoR/Unicorn is relatively heavyweight, in environment where there are a lot of simultaneous requests to get raw blobs, this works very slow and server is constantly overloaded. On the other hand, to get raw blob content, we do not need anything from RoR framework - we only need to have access to project git repository on filesystem, and knowing whether access for getting data from there should be granted or not. That means it is possible to handle '.../raw/....' request directly in more lightweight and performant gitlab-workhorse. As gitlab-workhorse is written in Go, and Go has good concurrency/parallelism support and is generally much faster than Ruby, moving raw blob serving task to it makes sense and should be a net win. In this patch: we add infrastructure to process GET request for '/raw/...': - extract project / ref and path from URL - query auth backend for whether download access should be granted or not - emit blob content via spawning external `git cat-file` I've tried to mimic the output to be as close as the one emitted by RoR code, with the idea that for users the change should be transparent. As in this patch we do auth backend query for every request to get a blob, RoR code is still loaded very much, so essentially there is no speedup yet: (on a 8-CPU i7-3770S with 16GB of RAM, 2001:67c:1254:e:8b::c776 is on localhost) # without patch: request eventually goes to unicorn (9 unicorn workers) $ ./wrk -c40 -d10 -t1 --latency http://[2001:67c:1254:e:8b::c776]:7777/nexedi/slapos/raw/master/software/wendelin/software.cfg Running 10s test @ http://[2001:67c:1254:e:8b::c776]:7777/nexedi/slapos/raw/master/software/wendelin/software.cfg 1 threads and 40 connections Thread Stats Avg Stdev Max +/- Stdev Latency 461.16ms 63.44ms 809.80ms 84.18% Req/Sec 84.84 17.02 131.00 80.00% Latency Distribution 50% 460.21ms 75% 492.83ms 90% 524.67ms 99% 636.49ms 847 requests in 10.01s, 1.57MB read Requests/sec: 84.64 Transfer/sec: 161.10KB # with this patch: request handled by gitlab-workhorse $ ./wrk -c40 -d10 -t1 --latency http://[2001:67c:1254:e:8b::c776]:7777/nexedi/slapos/raw/master/software/wendelin/software.cfg Running 10s test @ http://[2001:67c:1254:e:8b::c776]:7777/nexedi/slapos/raw/master/software/wendelin/software.cfg 1 threads and 40 connections Thread Stats Avg Stdev Max +/- Stdev Latency 458.42ms 66.26ms 766.12ms 84.76% Req/Sec 85.38 16.59 120.00 82.00% Latency Distribution 50% 459.26ms 75% 490.09ms 90% 523.95ms 99% 611.33ms 853 requests in 10.01s, 1.51MB read Requests/sec: 85.18 Transfer/sec: 154.90KB In the next patch we'll cache requests to auth backend and that will improve performance dramatically. NOTE 20160228: there is internal/git/blob.go trying to get raw data via gitlab-workhorse, but still asking Unicorn about blob->sha1 mapping etc. That work started in 86aaa133 (Prototype blobs via workhorse, @jacobvosmaer) and was inspired by this patch. It goes out of line compared to what we can do if we serve all blob data just by gitlab-workhorse (see next patch), so we just avoid git/blob.go and put our stuff into git/xblob.go and tweak routes, essentially deactivating git/blob.go code.
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