The LTTng Documentation
=======================
Philippe Proulx <pproulx@efficios.com>
-v2.8, 24 July 2017
+v2.8, 25 February 2021
include::../common/copyright.txt[]
_tracing session mode_ dictates where to send it. The following modes
are available in LTTng{nbsp}{revision}:
-Local mode::
+[[local-mode]]Local mode::
LTTng writes the traces to the file system of the machine being traced
(target system).
-Network streaming mode::
+[[net-streaming-mode]]Network streaming mode::
LTTng sends the traces over the network to a
<<lttng-relayd,relay daemon>> running on a remote system.
or to send it over the network to a <<lttng-relayd,relay daemon>>
running on a remote system.
-Live mode::
+[[live-mode]]Live mode::
This mode is similar to the network streaming mode, but a live
trace viewer can connect to the distant relay daemon to
<<lttng-live,view event records as LTTng generates them>> by
fit.
In discard mode, LTTng increments a count of lost event records when an
-event record is lost and saves this count to the trace. In overwrite
-mode, since LTTng 2.8, LTTng increments a count of lost sub-buffers when
-a sub-buffer is lost and saves this count to the trace. In this mode,
-the exact number of lost event records in those lost sub-buffers is not
-saved to the trace. Trace analyses can use the trace's saved discarded
-event record and sub-buffer counts to decide whether or not to perform
-the analyses even if trace data is known to be missing.
+event record is lost and saves this count to the trace. Since
+LTTng{nbsp}2.8, in overwrite mode, LTTng writes to a given sub-buffer
+its sequence number within its data stream. With a <<local-mode,local>>,
+<<net-streaming-mode,network streaming>>, or <<live-mode,live>>
+<<tracing-session,tracing session>>, a trace reader can use such
+sequence numbers to report lost packets. In overwrite mode, LTTng
+doesn't write to the trace the exact number of lost event records in
+those lost sub-buffers.
+
+Trace analyses can use saved discarded event record and sub-buffer
+(packet) counts of the trace to decide whether or not to perform the
+analyses even if trace data is known to be missing.
There are a few ways to decrease your probability of losing event
records.
[[prebuilt-ust-helpers]]
=== Prebuilt user space tracing helpers
-The LTTng-UST package provides a few helpers in the form or preloadable
+The LTTng-UST package provides a few helpers in the form of preloadable
shared objects which automatically instrument system functions and
calls.