2.8, 2.9, 2.10: since 2.8, LTTng keeps lost sub-buffer count in overwrite mode

[lttng-docs.git] / 2.10 / lttng-docs-2.10.txt

diff --git a/2.10/lttng-docs-2.10.txt b/2.10/lttng-docs-2.10.txt
index 37117b0b6c07ae8d9262465682a789a248af0440..10d1f443d4a38edc0d0684ed4501a9d54c9e46c6 100644 (file)
--- a/2.10/lttng-docs-2.10.txt
+++ b/2.10/lttng-docs-2.10.txt
@@ -1308,15 +1308,19 @@ always keep a fixed amount of the latest data.
 Which mechanism you should choose depends on your context: prioritize
 the newest or the oldest event records in the ring buffer?
 
-Beware that, in overwrite mode, the tracer abandons a whole sub-buffer
+Beware that, in overwrite mode, the tracer abandons a _whole sub-buffer_
 as soon as a there's no space left for a new event record, whereas in
 discard mode, the tracer only discards the event record that doesn't
 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, LTTng keeps no information when it overwrites a
-sub-buffer before consuming it.
+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.
 
 There are a few ways to decrease your probability of losing event
 records.