RFR: JMC-5327: Using HdrHistograms to visualize latencies

[Marcus Hirt]

We really should automate the verification of formatting, line ending
whitespaces and possibly allow the application of formatting from the
command line too. I'll look into adding spotless or something similar.

/M

On Thu, May 2, 2019 at 6:56 PM Alex Macdonald <almacdon at redhat.com> wrote:

> Hi Elliott,
>
> Overall this patch looks good to me. I've had Travis give it a build and it
> looks good [2].
>
> A handful of minor formatting nits:
>
> - Messages.properties (x3)
> - - the DurationPercentileTable_PERCENTILE_COL_NAME should come after
> DUMP_RECORDING_* for alphabetical order I believe
>
> - There are some cases of extra whitespace, I went through hg diff and
> counted the following number of occurrences:
> - - DurationHdrHistogram (8)
> - - DurationPercentileTable (38)
> - - FileIOPage (5)
> - - SocketIOPage (6)
> - - IOPageTest (5)
> - - IOPageTestBase (4)
> - - SocketIOPageTest(5)
>
> I noticed that when resizing the page, the durations table stays static
> whereas the other tables seems to adjust (gif) [3]. This only seems to
> cause an issue when my JMC window gets resized to just under 50% on my
> monitor width, and the chart will get hidden. In the gif my JMC window is
> around half my monitor width (of 1920), and with the JVM Browser/Outline
> window open then I don't have much more room to shrink the application
> before the chart disappears. I was just curious if the table could adjust
> to resizing like the other tables.
>
> Also not caused by this patch (but thought it'd be interesting to share),
> I'm seeing a bug where my chart text gets really large [4] when I run JMC
> locally and not as an RCP application (I recall seeing a JIRA bug for this
> before, but cannot find it), and my durations tab will only show the table
> (and not even the whole thing) [5].
>
> On Wed, May 1, 2019 at 1:01 PM Elliott Baron <ebaron at redhat.com> wrote:
>
> > Hi,
> >
> > Please review this patch which adds additional IO duration statistics
> > using HdrHistogram [1]. One of the nice features of HdrHistogram is its
> > ability to generate percentile distributions of data, while using
> > limited space. For latency measurements, this can be a useful tool to
> > draw attention to outliers where latency is particularly bad.
> >
> > These statistics are displayed in a new table within the File and Socket
> > IO pages. This table shows the read/write duration at predetermined
> > percentiles (0, 90, 99, 99.9, 99.99, 99.999, and 100), and the total
> > number of items <= that duration. I originally planned to show this
> > information in a chart, but ran into difficulties expressing a
> > non-linear percentile axis with JMC's charting API. After discussions
> > with Marcus, I opted to display this information using a table alongside
> > the existing chart.
> >
> > I included some UI tests that verify the values in each of these
> > HdrHistogram tables using a new (gzipped) JFR recording. I tried to keep
> > this recording as small as possible, while still getting somewhat
> > interesting results in the tables.
> >
> > HdrHistogram itself is already bundled on Maven Central, I simply added
> > it to our third-party p2 repository and target platforms. The included
> > translations for the word "percentile" are the result of consulting
> > online dictionaries, there may be better terms.
> >
> > Bug: https://bugs.openjdk.java.net/browse/JMC-5327
> > Webrev: http://cr.openjdk.java.net/~aptmac/JMC-5327/webrev.00/
> > Preview: https://imgur.com/a/MlA2C7y
> >
> > Thanks,
> > Elliott
> >
> > [1] http://hdrhistogram.org/
>
>
> Cheers,
>
> Alex
>
> [2] https://travis-ci.org/aptmac/jmc-qa/builds/527337343
> [3] https://imgur.com/XfkFqkI
> [4] https://imgur.com/Zii9nzw
> [5] https://imgur.com/Wyh6nbs
>