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 wait a variable amount of time. It is at most
proxy.config.thread.max_heartbeat_msecondsmilliseconds. It is reduced to the amount of time until the next scheduled event. Although this is done in milliseconds, system timers are rarely that accurate.For each network connection dispatch an event to the corresponding network virtual connection object.
Dispatch any events generated while handling I/O in the previous step
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”.
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.
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.
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.