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

[lttng-docs.git] / 2.9 / lttng-docs-2.9.txt

diff --git a/2.9/lttng-docs-2.9.txt b/2.9/lttng-docs-2.9.txt
index 9d3b864ee3412795841a0797bc568c16c17368ac..2457b8c00ef53ad4a5a79711c0690e4843876e62 100644 (file)
--- a/2.9/lttng-docs-2.9.txt
+++ b/2.9/lttng-docs-2.9.txt
@@ -1592,10 +1592,14 @@ 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.
@@ -1775,7 +1779,7 @@ With so many similar terms, it's easy to get confused.
 An **event** is the consequence of the execution of an _instrumentation
 point_, like a tracepoint that you manually place in some source code,
 or a Linux kernel KProbe. An event is said to _occur_ at a specific
-time. Different actions can be taken upon the occurance of an event,
+time. Different actions can be taken upon the occurrence of an event,
 like record the event's payload to a buffer.
 
 An **event record** is the representation of an event in a sub-buffer. A
@@ -7438,7 +7442,7 @@ event::
   or a Linux kernel KProbe.
 +
 An event is said to _occur_ at a specific time. Different actions can
-be taken upon the occurance of an event, like record the event's payload
+be taken upon the occurrence of an event, like record the event's payload
 to a sub-buffer.
 
 <<channel-overwrite-mode-vs-discard-mode,event loss mode>>::