X-Git-Url: https://git.lttng.org/?a=blobdiff_plain;f=2.10%2Flttng-docs-2.10.txt;h=10d1f443d4a38edc0d0684ed4501a9d54c9e46c6;hb=4089946d835f19eb1338c62f6eaf76f4a91da8e6;hp=58bbdf5967130f64fac218369451b08c4791c262;hpb=d2a86fb97c663ac2b1ae9344415b029f504578a6;p=lttng-docs.git diff --git a/2.10/lttng-docs-2.10.txt b/2.10/lttng-docs-2.10.txt index 58bbdf5..10d1f44 100644 --- a/2.10/lttng-docs-2.10.txt +++ b/2.10/lttng-docs-2.10.txt @@ -1,7 +1,7 @@ The LTTng Documentation ======================= Philippe Proulx -v2.10, 31 July 2017 +v2.10, 1 August 2017 include::../common/copyright.txt[] @@ -1290,8 +1290,11 @@ reached, the channel's _event loss mode_ determines what to do. The available event loss modes are: Discard mode:: - Drop the newest event records until a the tracer - releases a sub-buffer. + Drop the newest event records until a the tracer releases a + sub-buffer. ++ +This is the only available mode when you specify a +<>. Overwrite mode:: Clear the sub-buffer containing the oldest event records and start @@ -1305,15 +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. @@ -6792,7 +6799,7 @@ int main(int argc, char *argv[]) /* * Create a notification channel. A notification channel * connects the user application to the LTTng session daemon. - * This notification channel can be used to listen for various + * This notification channel can be used to listen to various * types of notifications. */ notification_channel = lttng_notification_channel_create( @@ -6801,8 +6808,9 @@ int main(int argc, char *argv[]) /* * Create a "high buffer usage" condition. In this case, the * condition is reached when the buffer usage is greater than or - * equal to 75 %. We create the condition for a specific session - * name, channel name, and for the user space tracing domain. + * equal to 75 %. We create the condition for a specific tracing + * session name, channel name, and for the user space tracing + * domain. * * The "low buffer usage" condition type also exists. */ @@ -6836,11 +6844,12 @@ int main(int argc, char *argv[]) * notification, we must subscribe to notifications that match * the same condition. */ - lttng_notification_channel_subscribe(notification_channel, condition); + lttng_notification_channel_subscribe(notification_channel, + condition); /* - * Notification loop. This can be in a dedicated thread to avoid - * blocking the main thread. + * Notification loop. You can put this in a dedicated thread to + * avoid blocking the main thread. */ for (;;) { struct lttng_notification *notification; @@ -6851,8 +6860,7 @@ int main(int argc, char *argv[]) /* Receive the next notification. */ status = lttng_notification_channel_get_next_notification( - notification_channel, - ¬ification); + notification_channel, ¬ification); switch (status) { case LTTNG_NOTIFICATION_CHANNEL_STATUS_OK: @@ -6887,7 +6895,7 @@ int main(int argc, char *argv[]) * condition. * * The condition evaluation provides the buffer usage - * value at the moment the condition was met. + * value at the moment the condition was reached. */ notification_condition = lttng_notification_get_condition( notification); @@ -6911,9 +6919,8 @@ int main(int argc, char *argv[]) * usage, like disable specific events. */ printf("Buffer usage is %f %% in tracing session \"%s\", " - "user space channel \"%s\".\n", - buffer_usage * 100, tracing_session_name, - channel_name); + "user space channel \"%s\".\n", buffer_usage * 100, + tracing_session_name, channel_name); lttng_notification_destroy(notification); }