[lttng-dev] [RELEASE] LTTng-Tools 2.8.0-rc1

[Jérémie Galarneau]

Hi everyone!

Today marks the release of the first LTTng 2.8 - "Isseki Nicho"
release candidate.

The result of a collaboration between Dieu du Ciel! and Nagano-based
Shiga Kogen, Isseki Nicho is a strong Imperial Dark Saison offering a
rich roasted malt flavor combined with a complex fruity finish typical
of Saison yeasts.


This new release introduces the following major features:

--- Java Application Contexts ---
This new feature allows dynamic application contexts to be both saved
to a trace and used as an event filtering criterion.

An example showing how to define and populate Application Contexts is
provided as part of LTTng-UST's examples.

https://github.com/lttng/lttng-ust/blob/master/doc/examples/java-jul/ApplicationContextExample.java

Application contexts can be added to a channel by using, for example:
$ lttng add-context --jul -t '$app.retriever_name:context_name'

They can also be used to filter events:
$ lttng enable-event --jul my_application_event --filter
'$app.retriever_name:context_name > 52'

See the lttng-enable-event(1) and lttng-add-context(1) man pages for
more information.


--- Metadata Regeneration ---
A number of users have been using LTTng to trace embedded systems,
which often boot with an unset clock, before any NTP correction could
occur. Since the wall-time would be sampled before any NTP correction,
viewers would generally show traces as having been recorded at an
incorrect point in time.

This new command, lttng metadata regenerate, forces LTTng to resample
the current wall-time to determine an appropriate offset and
regenerate a trace's metadata.

For more information on this command and its limitations, please refer
to lttng-metadata(1).


--- Overhauled Man pages ---
As you may have noticed, LTTng commands now have their own individual
man pages. These are now also displayed when a command's "--help"
option is used.

Of particular interest to our packagers is the fact that man pages
must now be generated using the --enable-build-man-pages configuration
option.
The generation of man pages requires both AsciiDoc >= 8.4.5 and xmlto
>= 0.0.21 to be installed on the system. However, note that official
"tarball" releases will contain the generated man pages.


--- Discarded Events and Lost Packets Statistics ---
This release adds discarded events and lost packets accounting which
allows the LTTng client to print a warning when the tracer was forced
to discard events or overwrite packets. The warnings take the
following form:
[warning] 1234 events discarded, please refer to the documentation on
channel configuration.
or
[warning] 1234 packets, please refer to the documentation on channel
configuration.

We have decided to add these warnings since a growing number of users
have been running analyses based on traces, the result of which may be
unreliable when events or packets are dropped.

A new packet sequence number was also added to the trace's packet
context. This allows viewers to indicate lost packets when the
"overwrite" mode is being used. See the LTTng documentation for a
detailed explanation of discard and overwrite modes.

https://lttng.org/docs/#doc-channel-overwrite-mode-vs-discard-mode


We will cover all of these new features in depth in an upcoming post
on the official LTTng blog at lttng.org/blog in time for the final
release.
The official documentation will also be updated to reflect the
addition of these new features.

As always, please report any issue you may encounter to bugs.lttng.org
or on this mailing list.

Project website: https://lttng.org

Download links:
https://lttng.org/files/lttng-tools/lttng-tools-2.8.0-rc1.tar.bz2
GPG sig: https://lttng.org/files/lttng-tools/lttng-tools-2.8.0-rc1.tar.bz2.asc

Looking forward to your feedback!

-- 
Jérémie Galarneau
EfficiOS Inc.
http://www.efficios.com