Get flow statistics
- Base URL
-
/
- GET /_node/stats/flow
Get throughput and backpressure details.
Response
Flow rates provide visibility into how a Logstash instance or an individual pipeline is currently performing relative to itself over time. This allows us to attach meaning to the cumulative-value metrics that are also presented by this API, and to determine whether an instance or pipeline is behaving better or worse than it has in the past.
The following flow rates are available for the logstash process as a whole and for each of its pipelines individually. In addition, pipelines may have additional flow rates depending on their configuration.
-
flowobject -
input_throughputobject -
This metric is expressed in events-per-second, and is the rate of events being pushed into the pipeline(s) queue(s) relative to wall-clock time (
events.in/ second). It includes events that are blocked by the queue and have not yet been accepted. -
filter_throughputobject -
This metric is expressed in events-per-second, and is the rate of events flowing through the filter phase of the pipeline(s) relative to wall-clock time (
events.filtered/ second). -
output_throughputobject -
This metric is expressed in events-per-second, and is the rate of events flowing through the output phase of the pipeline(s) relative to wall-clock time (
events.out/ second). -
queue_backpressureobject -
This is a unitless metric representing the cumulative time spent by all inputs blocked pushing events into their pipeline’s queue, relative to wall-clock time (queue_push_duration_in_millis / millisecond). It is typically most useful when looking at the stats for an individual pipeline.
While a "zero" value indicates no back-pressure to the queue, the magnitude of this metric is highly dependent on the shape of the pipelines and their inputs. It cannot be used to compare one pipeline to another or even one process to itself if the quantity or shape of its pipelines changes. A pipeline with only one single-threaded input may contribute up to 1.00, a pipeline whose inputs have hundreds of inbound connections may contribute much higher numbers to this combined value.
Additionally, some amount of back-pressure is both normal and expected for pipelines that are pulling data, as this back-pressure allows them to slow down and pull data at a rate its downstream pipeline can tolerate.
-
worker_concurrencyobject -
This is a unitless metric representing the cumulative time spent by all workers relative to wall-clock time (duration_in_millis / millisecond).
A pipeline is considered "saturated" when its worker_concurrency flow metric approaches its available pipeline.workers, because it indicates that all of its available workers are being kept busy. Tuning a saturated pipeline to have more workers can often work to increase that pipeline’s throughput and decrease back-pressure to its queue, unless the pipeline is experiencing back-pressure from its outputs.
A process is also considered "saturated" when its top-level worker_concurrency flow metric approaches the cumulative pipeline.workers across all pipelines, and similarly can be addressed by tuning the individual pipelines that are saturated.