From: Jeff Hostetler <firstname.lastname@example.org>
To: Josh Steadmon <email@example.com>,
Derrick Stolee <firstname.lastname@example.org>,
Subject: Re: [RFC PATCH v3 3/3] trace2: write overload message to sentinel files
Date: Thu, 19 Sep 2019 14:23:48 -0400 [thread overview]
Message-ID: <email@example.com> (raw)
On 9/16/2019 2:20 PM, Josh Steadmon wrote:
> On 2019.09.16 10:11, Jeff Hostetler wrote:
>> On 9/16/2019 8:07 AM, Derrick Stolee wrote:
>>> On 9/13/2019 8:26 PM, Josh Steadmon wrote:
>>>> Add a new "overload" event type for trace2 event destinations. Write
>>>> this event into the sentinel file created by the trace2.maxFiles
>>>> feature. Bump up the event format version since we've added a new event
>>>> Writing this message into the sentinel file is useful for tracking how
>>>> often the overload protection feature is triggered in practice.
>>> Putting meaningful data into the sentinel file is valuable. It's
>>> important to know a bit about when and why this happened. A user
>>> would be able to inspect the modified time, and the directory info
>>> you include is unnecessary. The data you include is only for the
>>> log aggregator to keep valuable data around overloads.
>>>> + This event is created in a sentinel file if we are overloading a target
>>>> + trace directory (see the trace2.maxFiles config option).
>>>> + "event":"overload",
>>>> + ...
>>>> + "dir":"/trace/target/dir/", # The configured trace2 target directory
>>>> + "evt":"2", # EVENT format version
>>> That said, do we really need to resort to a new event format and
>>> event type? Could we instead use the "data" event with a key
>>> "overload" and put the target dir in the value?
>> If I understand the code here, the overload event/message is
>> only written to the sentinel file -- it is not written to a
>> regular trace2 log file, so regular log file consumers will
>> never see this event, right?
> Well, I guess it's hard to define what is a "regular log file consumer".
> In our case, our collection system will treat sentinel files like any
> other trace file, so it's useful to have it match the expected trace
> At least for our use, we don't want the sentinel files treated
> specially, because we want the log collection system to just do its
> thing and remove the file after processing, which lets Git know that
> it's ok to start writing traces again.
>> That message could be in any format, right? And you could write
>> as much or as little data into the sentinel file as you want.
> To me it seems that it would be less surprising on the users' side if
> any data written to the sentinel file matches the format of the
> requested traces. If I have an automated process that's reading JSON
> from a directory full of files, I don't want to have to add a special
> case where one file might have perf-format data (or vice versa).
>> There's no compelling reason to extend the existing trace2 format
>> to have a new message type, so I'm not seeing a reason to add the
>> event-type nor to increment the version number.
>> The existing trace2 formats and messages/event-types are defined
>> and driven by the Trace2 API calls presented to upper layers
>> (consumers of the public trace2_*() functions and macros defined
>> in trace2.h). This overload event doesn't fit that model.
> Yeah, I did feel like this might be overkill. Do you think Stolee's
> suggestion to use a "data" event instead would be acceptable?
>> I think it'd be better to just directly write() a message -- in
>> plain-text or JSON or whatever -- in tr2_create_sentinel() and
>> not try to piggy-back on the existing format machinery in the
>> tr2_tgt_*.c files.
> I had a version that did this originally, but I don't really like having
> an unexpected special case where we just write a static JSON string. It
> feels like an ugly corner case, and would be surprising to users, IMO.
> But if everyone thinks this is a better approach, I suppose I could just
> add a switch statement in tr2_create_sentinel() that looks at the
> sysenv_var field of the tr2_dst.
You make some good points. I suppose it would be good to be able
to parse the overload file using the same reader/scheme as the
other events. Well, at least for the JSON format; the other formats
don't really matter for your purposes anyway.
I am concerned that the new "overload" event will be the only event
in the file and therefore replace the "version" event in those files.
That is, we'll break the invariant that all JSON files begin with a
"version" event that containing the event version string. That is,
in the current proposal, the format becomes:
v2 ::= <overload> | <<v1>>
v1 ::= <version> <start> ... <atexit>
V1 readers were promised that the first event in the file would
always be a <version> event. And that they can dispatch on the
version.evt field. V1 readers won't recognize the <overload> event
and they won't know to look at the overload.evt field. That might
cause V1 parsers to throw a harder error than a simpler version
Just using a "data" event also feels wrong for the same reasons.
At that point in tr2_create_sentinel(), a new "data" event would
just give us:
V2 ::= <data key="overload", value="true"> | <<v1>>
v1 ::= <version> <start> ... <atexit>
Having said that I wonder if it would be better to have
tr2_create_sentinel() just set a flag (and leave the fd open).
And then either add the new event as:
V2 ::= <version evt=2> <overload dir=path, max=n> | <<v1>>
or just add a column to the <version> event (and go ahead and
let the overload file be a full trace2 log from the command):
V1 ::= <version evt=1, [overload=true]> <start> ... <atexit>
Does that make sense??
next prev parent reply other threads:[~2019-09-19 18:23 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-29 22:20 [RFC PATCH] trace2: don't overload target directories 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
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 [this message]
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
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
List information: http://vger.kernel.org/majordomo-info.html
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
Code repositories for project(s) associated with this public inbox
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).