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vatamane pushed a commit to branch main
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The following commit(s) were added to refs/heads/main by this push:
new 2bbc89ce1 Use milliseconds for fsync time histogram
2bbc89ce1 is described below
commit 2bbc89ce1ef4c7eb3afbdbfaee41113e4c869cf0
Author: Nick Vatamaniuc <[email protected]>
AuthorDate: Mon May 22 22:57:12 2023 -0400
Use milliseconds for fsync time histogram
Most of our histograms are in milliseconds. Don't deviate from that with the
new fsync.time metric so make it use milliseconds as well. It turns out
fractional histogram values are allowed, so we can still get the
sub-millisecond precision for faster disks that way.
Example of usage during: `fabric_bench:go(#{docs=>50000, batch_size=>100}).`
```
couch_stats:sample([fsync, time]).
[{min,8.303},
{max,134.124},
{arithmetic_mean,49.3490064102564},
{geometric_mean,42.939511193319994},
{harmonic_mean,37.05011500299417},
{median,43.198},
{variance,654.1673972451199},
{standard_deviation,25.57669637082006},
{skewness,0.7276971171556265},
{kurtosis,-0.021701320829371706},
{percentile,[{50,43.198},
{75,63.858},
{90,81.22},
{95,97.231},
{99,114.86},
{999,134.124}]},
{histogram,[{25.303,48},
{48.303,40},
{68.303,38},
{78.303,4},
{98.303,18},
{118.303,7},
{128.303,0},
{148.303,1}]},
{n,156}]
```
---
src/couch/src/couch_file.erl | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/src/couch/src/couch_file.erl b/src/couch/src/couch_file.erl
index d68f8c49c..51b0e69e0 100644
--- a/src/couch/src/couch_file.erl
+++ b/src/couch/src/couch_file.erl
@@ -643,10 +643,13 @@ format_status(_Opt, [PDict, #file{} = File]) ->
[{data, [{"State", File}, {"InitialFilePath", FilePath}]}].
fsync(Fd) ->
+ % Our metrics histograms are in milliseconds so stick to that pattern.
+ % However we measure the time delta in microseconds so we get fractional
+ % microseconds for cases when the disk drives are faster.
T0 = erlang:monotonic_time(microsecond),
Res = file:sync(Fd),
- Dt = erlang:monotonic_time(microsecond) - T0,
- couch_stats:update_histogram([fsync, time], Dt),
+ DtUSec = erlang:monotonic_time(microsecond) - T0,
+ couch_stats:update_histogram([fsync, time], DtUSec / 1000),
couch_stats:increment_counter([fsync, count]),
Res.
