Event Loop¶
The core of network processing in Traffic Server is the event loop. This loop executes any pending events and performs I/O operations on network connections. The time spent in the event loop is a critical component of latency as any network connection has at most one I/O operation per loop. The general mechanism is
Dispatch any pending events.
Check for any pending I/O activity. This waits a variable amount of time, but at most
proxy.config.thread.max_heartbeat_msecondsmilliseconds. It is reduced to wake up before the next scheduled event. Although this is done in milliseconds, system timers are rarely that accurate.For each network connection that has pending I/O, dispatch an event to the corresponding network virtual connection object.
Dispatch any events generated while handling I/O in the previous steps.
Event loops that take a long time will have a noticeable impact on transaction latency. There are a number of statistics gathered to help determine if this is the problem. Because instantaneous values are not useful, the data is gathered in three different time buckets - 10, 100, and 1000 seconds. There is a parallel set of statistics for each, and each larger time period includes the smaller ones. The statistic values are all “for this time period”. For example, the statistic “proxy.process.eventloop.count.100s” is “the number of event loops executed in the last 100 seconds”. The histogram metrics provide a more detailed look at the distribution of event loop times to distinguish whether long times are common or an outlier.
In general, the maximum loop time will create a floor under response latency. If that is frequently high then it is likely transactions are experiencing significant latency.
10 Second Metrics
- proxy.process.eventloop.count.10s¶
- Collection:
- global
- Datatype:
- integer
Number of event loops executed in the last 10 seconds.
- proxy.process.eventloop.events.10s¶
- Collection:
- global
- Datatype:
- integer
Number of events dispatched in the last 10 seconds.
- proxy.process.eventloop.events.min.10s¶
- Collection:
- global
- Datatype:
- integer
Minimum number of events dispatched in a single loop in the last 10 seconds.
- proxy.process.eventloop.events.max.10s¶
- Collection:
- global
- Datatype:
- integer
Maximum number of events dispatched in a single loop in the last 10 seconds.
- proxy.process.eventloop.wait.10s¶
- Collection:
- global
- Datatype:
- integer
Number of loops in which the I/O activity check was done with a non-zero time out in the last 10 seconds.
- proxy.process.eventloop.time.min.10s¶
- Collection:
- global
- Units:
- nanoseconds
- Datatype:
- integer
The minimum amount of time spent in a single loop in the last 10 seconds.
- proxy.process.eventloop.time.max.10s¶
- Collection:
- global
- Units:
- nanoseconds
- Datatype:
- integer
The maximum amount of time spent in a single loop in the last 10 seconds.
- proxy.process.eventloop.drain.queue.max.10s¶
- Collection:
- global
- Units:
- nanoseconds
- Datatype:
- integer
The maximum amount of time spent draining the event queue in a single loop in the last 10 seconds.
- proxy.process.eventloop.io.wait.max.10s¶
- Collection:
- global
- Units:
- nanoseconds
- Datatype:
- integer
The maximum amount of time spent waiting for network IO in a single loop in the last 10 seconds.
- proxy.process.eventloop.io.work.max.10s¶
- Collection:
- global
- Units:
- nanoseconds
- Datatype:
- integer
The maximum amount of time spent processing network IO in a single loop in the last 10 seconds.
100 Second Metrics
- proxy.process.eventloop.count.100s¶
- Collection:
- global
- Datatype:
- integer
Number of event loops executed in the last 100 seconds.
- proxy.process.eventloop.events.100s¶
- Collection:
- global
- Datatype:
- integer
Number of events dispatched in the last 100 seconds.
- proxy.process.eventloop.events.min.100s¶
- Collection:
- global
- Datatype:
- integer
Minimum number of events dispatched in a single loop in the last 100 seconds.
- proxy.process.eventloop.events.max.100s¶
- Collection:
- global
- Datatype:
- integer
Maximum number of events dispatched in a single loop in the last 100 seconds.
- proxy.process.eventloop.wait.100s¶
- Collection:
- global
- Datatype:
- integer
Number of loops in which the I/O activity check was done with a non-zero time out in the last 100 seconds.
- proxy.process.eventloop.time.min.100s¶
- Collection:
- global
- Units:
- nanoseconds
- Datatype:
- integer
The minimum amount of time spent in a single loop in the last 100 seconds.
- proxy.process.eventloop.time.max.100s¶
- Collection:
- global
- Units:
- nanoseconds
- Datatype:
- integer
The maximum amount of time spent in a single loop in the last 100 seconds.
- proxy.process.eventloop.drain.queue.max.100s¶
- Collection:
- global
- Units:
- nanoseconds
- Datatype:
- integer
The maximum amount of time spent draining the event queue in a single loop in the last 100 seconds.
- proxy.process.eventloop.io.wait.max.100s¶
- Collection:
- global
- Units:
- nanoseconds
- Datatype:
- integer
The maximum amount of time spent waiting for network IO in a single loop in the last 100 seconds.
- proxy.process.eventloop.io.work.max.100s¶
- Collection:
- global
- Units:
- nanoseconds
- Datatype:
- integer
The maximum amount of time spent processing network IO in a single loop in the last 100 seconds.
1000 Second Metrics
- proxy.process.eventloop.count.1000s¶
- Collection:
- global
- Datatype:
- integer
Number of event loops executed in the last 1000 seconds.
- proxy.process.eventloop.events.1000s¶
- Collection:
- global
- Datatype:
- integer
Number of events dispatched in the last 1000 seconds.
- proxy.process.eventloop.events.min.1000s¶
- Collection:
- global
- Datatype:
- integer
Minimum number of events dispatched in a single loop in the last 1000 seconds.
- proxy.process.eventloop.events.max.1000s¶
- Collection:
- global
- Datatype:
- integer
Maximum number of events dispatched in a single loop in the last 1000 seconds.
- proxy.process.eventloop.wait.1000s¶
- Collection:
- global
- Datatype:
- integer
Number of loops in which the I/O activity check was done with a non-zero time out in the last 1000 seconds.
- proxy.process.eventloop.time.min.1000s¶
- Collection:
- global
- Units:
- nanoseconds
- Datatype:
- integer
The minimum amount of time spent in a single loop in the last 1000 seconds.
- proxy.process.eventloop.time.max.1000s¶
- Collection:
- global
- Units:
- nanoseconds
- Datatype:
- integer
The maximum amount of time spent in a single loop in the last 1000 seconds.
- proxy.process.eventloop.drain.queue.max.1000s¶
- Collection:
- global
- Units:
- nanoseconds
- Datatype:
- integer
The maximum amount of time spent draining the event queue in a single loop in the last 1000 seconds.
- proxy.process.eventloop.io.wait.max.1000s¶
- Collection:
- global
- Units:
- nanoseconds
- Datatype:
- integer
The maximum amount of time spent waiting for network IO in a single loop in the last 1000 seconds.
- proxy.process.eventloop.io.work.max.1000s¶
- Collection:
- global
- Units:
- nanoseconds
- Datatype:
- integer
The maximum amount of time spent processing network IO in a single loop in the last 1000 seconds.
Histogram Metrics
- proxy.process.eventloop.time.*ms¶
- Collection:
- global
- Datatype:
- integer
This is a set of statistics that provide a histogram of event loop times. Each is labeled with a value indicating the minimum time for the bucket. The maximum is less than the minimum of the next bucket. E.g. there is a “10ms” and a “20ms” statistic. The “10ms” statistic counts the number of times the event loop took at least 10ms and less than 20ms. The exception is the last bucket which has no maximum. The histogram is semi-logarithmic so that bucket sizes increase exponentially with smaller intermediate steps. Every 60 seconds the accumulated values are decreased by half to provide an exponential decay of recent activity. The current set of statistics is
proxy.process.eventloop.time.0ms 2210
proxy.process.eventloop.time.5ms 293
proxy.process.eventloop.time.10ms 1848
proxy.process.eventloop.time.15ms 1483
proxy.process.eventloop.time.20ms 0
proxy.process.eventloop.time.25ms 0
proxy.process.eventloop.time.30ms 0
proxy.process.eventloop.time.35ms 348
proxy.process.eventloop.time.40ms 0
proxy.process.eventloop.time.50ms 0
proxy.process.eventloop.time.60ms 23872
proxy.process.eventloop.time.70ms 0
proxy.process.eventloop.time.80ms 0
proxy.process.eventloop.time.100ms 0
proxy.process.eventloop.time.120ms 0
proxy.process.eventloop.time.140ms 0
proxy.process.eventloop.time.160ms 0
proxy.process.eventloop.time.200ms 0
proxy.process.eventloop.time.240ms 0
proxy.process.eventloop.time.280ms 0
proxy.process.eventloop.time.320ms 0
proxy.process.eventloop.time.400ms 0
proxy.process.eventloop.time.480ms 0
proxy.process.eventloop.time.560ms 0
proxy.process.eventloop.time.640ms 0
proxy.process.eventloop.time.800ms 0
proxy.process.eventloop.time.960ms 0
proxy.process.eventloop.time.1120ms 0
proxy.process.eventloop.time.1280ms 0
proxy.process.eventloop.time.1600ms 0
proxy.process.eventloop.time.1920ms 0
proxy.process.eventloop.time.2240ms 0
proxy.process.eventloop.time.2560ms 0
This is an idle instance therefore the values are clustered strongly on 0 (less than 5ms) and 60ms (the default wait for I/O timeout).
- proxy.process.api.time.*ms¶
- Collection:
- global
- Datatype:
- integer
A set of statistics that provide a histogram of total time spent in plugins. This is sampled
per plugin, rather than the aggregate value for milestone TS_MILESTONE_PLUGIN_TOTAL.
See proxy.process.eventloop.time.*ms for technical details.