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From: Josh Steadmon <steadmon@google.com>
To: Jeff Hostetler <git@jeffhostetler.com>
Cc: git@vger.kernel.org, stolee@gmail.com
Subject: Re: [RFC PATCH v2 2/2] trace2: don't overload target directories
Date: Mon, 5 Aug 2019 11:17:55 -0700	[thread overview]
Message-ID: <20190805181755.GU43313@google.com> (raw)
In-Reply-To: <b1009a3e-92c6-248c-8d15-f4bb5cc71a11@jeffhostetler.com>

On 2019.08.05 11:34, Jeff Hostetler wrote:
> 
> 
> On 8/2/2019 6:02 PM, Josh Steadmon wrote:
> > trace2 can write files into a target directory. With heavy usage, this
> > directory can fill up with files, causing difficulty for
> > trace-processing systems.
> > 
> > This patch adds a config option (trace2.maxFiles) to set a maximum
> > number of files that trace2 will write to a target directory. The
> > following behavior is enabled when the maxFiles is set to a positive
> > integer:
> >    When trace2 would write a file to a target directory, first check
> >    whether or not the directory is overloaded. A directory is overloaded
> >    if there is a sentinel file declaring an overload, or if the number of
> >    files exceeds trace2.maxFiles. If the latter, create a sentinel file
> >    to speed up later overload checks.
> > 
> > The assumption is that a separate trace-processing system is dealing
> > with the generated traces; once it processes and removes the sentinel
> > file, it should be safe to generate new trace files again.
> > 
> > The default value for trace2.maxFiles is zero, which disables the
> > overload check.
> > 
> > The config can also be overridden with a new environment variable:
> > GIT_TRACE2_MAX_FILES.
> > 
> > Potential future work:
> > * Write a message into the sentinel file (should match the requested
> >    trace2 output format).
> > * Add a performance test to make sure that contention between multiple
> >    processes all writing to the same target directory does not become an
> >    issue.
> 
> 
> This looks much nicer than the V1 version.  Having it be a
> real feature rather than a test feature helps.
> 
> I don't see anything wrong with this.  I do worry about the
> overhead a bit.  If you really have that many files in the
> target directory, having every command count them at startup
> might be an issue.
> 
> As an alternative, you might consider doing something like
> this:
> 
> [] have an option to make the target directory path expand to
>    something like "<path>/yyyymmdd/" and create the per-process
>    files as "<path>/yyyymmdd/<sid>".
> 
> If there are 0, 1 or 2 directories, logging is enabled.
> We assume that the post-processor is keeping up and all is well.
> We need to allow 2 so that we continue to log around midnight.
> 
> If there are 3 or more directories, logging is disabled.
> The post-processor is more than 24 hours behind for whatever
> reason.  We assume here that the post-processor will process
> and delete the oldest-named directory, so it is a valid measure
> of the backlog.
> 
> I suggest "yyyymmdd" here for simplicity in this discussion
> as daily log rotation is common.  If that's still overloading,
> you could make it a longer prefix of the <sid>.  And include
> the hour, for example.
> 
> I suggest 3 as the cutoff lower bound, because we need to allow
> 2 for midnight rotation.  But you may want to increase it to
> allow for someone to be offline for a long weekend, for example.
> 
> Anyway, this is just a suggestion.  It would give you the
> throttling, but without the need for every command to count
> the contents of the target directory.
> 
> And it would still allow your post-processor to operate in
> near real-time on the contents of the current day's target
> directory or to hang back if that causes too much contention.
> 
> Feel free to ignore this :-)
> 
> Jeff

This does sound reasonable. I'll talk with our collection team and see
if this would work without requiring any changes on their side. If not,
I'll probably take a stab at this when I'm back from vacation.

Thanks!

  reply	other threads:[~2019-08-05 18:18 UTC|newest]

Thread overview: 40+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-07-29 22:20 [RFC PATCH] " Josh Steadmon
2019-07-30 13:29 ` Derrick Stolee
2019-07-30 21:52   ` Josh Steadmon
2019-07-30 16:46 ` Jeff Hostetler
2019-07-30 22:01   ` Josh Steadmon
2019-07-30 22:02   ` Josh Steadmon
2019-07-30 18:00 ` Jeff Hostetler
2019-07-30 22:08   ` Josh Steadmon
2019-08-02 22:02 ` [RFC PATCH v2 0/2] " Josh Steadmon
2019-08-02 22:02   ` [RFC PATCH v2 1/2] docs: mention trace2 target-dir mode in git-config Josh Steadmon
2019-08-02 22:02   ` [RFC PATCH v2 2/2] trace2: don't overload target directories Josh Steadmon
2019-08-05 15:34     ` Jeff Hostetler
2019-08-05 18:17       ` Josh Steadmon [this message]
2019-08-05 18:01     ` SZEDER Gábor
2019-08-05 18:09       ` Josh Steadmon
2019-09-14  0:25 ` [RFC PATCH v3 0/3] " Josh Steadmon
2019-09-14  0:25   ` [RFC PATCH v3 1/3] docs: mention trace2 target-dir mode in git-config Josh Steadmon
2019-09-14  0:25   ` [RFC PATCH v3 2/3] trace2: don't overload target directories Josh Steadmon
2019-09-14  0:26   ` [RFC PATCH v3 3/3] trace2: write overload message to sentinel files Josh Steadmon
2019-09-16 12:07     ` Derrick Stolee
2019-09-16 14:11       ` Jeff Hostetler
2019-09-16 18:20         ` Josh Steadmon
2019-09-19 18:23           ` Jeff Hostetler
2019-09-19 22:47             ` Josh Steadmon
2019-09-20 15:59               ` Jeff Hostetler
2019-09-16 18:07       ` Josh Steadmon
2019-10-03 23:32 ` [PATCH v4 0/4] trace2: don't overload target directories Josh Steadmon
2019-10-03 23:32   ` [PATCH v4 1/4] docs: mention trace2 target-dir mode in git-config Josh Steadmon
2019-10-03 23:32   ` [PATCH v4 2/4] docs: clarify trace2 version invariants Josh Steadmon
2019-10-03 23:32   ` [PATCH v4 3/4] trace2: don't overload target directories Josh Steadmon
2019-10-04  0:25     ` Junio C Hamano
2019-10-04 21:57       ` Josh Steadmon
2019-10-04  9:12     ` Johannes Schindelin
2019-10-04 22:05       ` Josh Steadmon
2019-10-03 23:32   ` [PATCH v4 4/4] trace2: write overload message to sentinel files Josh Steadmon
2019-10-04 22:08 ` [PATCH v5 0/4] trace2: discard new traces if the target directory contains too many files Josh Steadmon
2019-10-04 22:08   ` [PATCH v5 1/4] docs: mention trace2 target-dir mode in git-config Josh Steadmon
2019-10-04 22:08   ` [PATCH v5 2/4] docs: clarify trace2 version invariants Josh Steadmon
2019-10-04 22:08   ` [PATCH v5 3/4] trace2: discard new traces if target directory has too many files Josh Steadmon
2019-10-04 22:08   ` [PATCH v5 4/4] trace2: write discard message to sentinel files Josh Steadmon

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