memorylimiterprocessor

README

Memory Limiter Processor

Status
Stability	alpha: profiles
	beta: traces, metrics, logs
Distributions	core, contrib, k8s
Issues

Overview

The memory limiter processor is used to prevent out of memory situations on the collector. Given that the amount and type of data the collector processes is environment-specific and resource utilization of the collector is also dependent on the configured processors, it is important to put checks in place regarding memory usage.

Functionality

The memory limiter processor performs periodic checks of memory usage and will begin refusing data and forcing GC to reduce memory consumption when defined limits have been exceeded.

The processor uses soft and hard memory limits. The hard limit is defined via the limit_mib configuration option, and is always above or equal to the soft limit. The difference between the soft limit and hard limit is defined via the spike_limit_mib configuration option.

The processor will enter memory limited mode and will start refusing the data when memory usage exceeds the soft limit. This is done by returning errors to the preceding component in the pipeline that made the ConsumeLogs/Trace/Metrics function call.

Warning: Incoming data can consume additional memory in a Collector before the memory limiter processor is able to reject it. Be sure to consider this when setting your limits, particularly for non-OTLP receivers.

See https://github.com/open-telemetry/opentelemetry-collector/issues/8632 for more.

In memory limited mode the error returned by ConsumeLogs/Trace/Metrics function is a non-permanent error. When receivers see this error they are expected to retry sending the same data. The receivers may also apply backpressure to their own data sources in order to slow the inflow of data into the Collector, and to allow memory usage to go below the set limits.

Warning: Data will be permanently lost if the component preceding the memory limiter in the telemetry pipeline does not correctly retry sending data after it has been refused by the memory limiter. We consider such components to be incorrectly implemented.

When the memory usage is above the hard limit the processor will additionally force garbage collection to be performed.

Normal operation is resumed when memory usage drops below the soft limit, meaning data will no longer be refused and the processor won't force garbage collection to be performed.

Forced GC may waste CPU without freeing memory if the data is held by live references elsewhere in the collector (for example, exporter queues during a downstream outage). The processor backs off forced GC exponentially when it is ineffective, and resets as soon as memory drops.

Best Practices

Note that while the processor can help mitigate out of memory situations, it is not a replacement for properly sizing and configuring the collector. Keep in mind that if the soft limit is crossed, the collector will return errors to all receive operations until enough memory is freed. This may eventually result in dropped data since the receivers may not be able to retry the data indefinitely.

It is highly recommended to configure the GOMEMLIMIT environment variable as well as the memory_limiter processor on every collector. GOMEMLIMIT should be set to 80% of the hard memory limit of your collector. For the memory_limiter processor, the best practice is to add it as the first processor in a pipeline. This is to ensure that backpressure can be sent to applicable receivers and minimize the likelihood of dropped data when the memory_limiter gets triggered.

The value of the spike_limit_mib configuration option should be selected in a way that ensures that memory usage cannot increase by more than this value within a single memory check interval. Otherwise, memory usage may exceed the hard limit, even if temporarily. A good starting point for spike_limit_mib is 20% of the hard limit. Bigger spike_limit_mib values may be necessary for spiky traffic or for longer check intervals.

It's recommended to coordinate the hard memory limit with the host environment of the Collector. As always, you know your environment best, so use your own judgement to determine the best configuration for your situation. However, the following points are worth considering when configuring the processor:

For containerized environments or other similar environments that support setting memory restrictions on the Collector, limit_percentage should generally be used, which allows the host environment to determine the Collector's max memory allocation without tying the Collector's own config to its deployment config. The percentage should be large enough to use the majority of the Collector's allocated memory, but not so much that it risks running out of memory.

For bare metal or virtualized environments where the Collector's memory is not constrained by the host environment, it is recommended to use limit_mib for environments where you know the rough data throughput and memory consumption you expect for a given Collector, regardless of the memory capacity of the machine it runs on. If the Collector's memory consumption is expected to scale with its host machine's memory capacity, limit_percentage may be more appropriate.

Configuration

Please refer to config.go for the config spec.

The following configuration options are available. Note that one of limit_mib or limit_percentage must be set.

• check_interval (default = 0s): Time between measurements of memory usage. The recommended value is 1 second. If the expected traffic to the Collector is very spiky then decrease the check_interval or increase spike_limit_mib to avoid memory usage going over the hard limit.
• limit_mib (default = 0): Maximum amount of memory, in MiB, targeted to be allocated by the process heap. Note that typically the total memory usage of process will be about 50MiB higher than this value. This defines the hard limit.
• spike_limit_mib (default = 20% of limit_mib): Maximum spike expected between the measurements of memory usage. The value must be less than limit_mib. The soft limit value will be equal to (limit_mib - spike_limit_mib). The recommended value for spike_limit_mib is about 20% limit_mib.
• limit_percentage (default = 0): Maximum amount of total memory targeted to be allocated by the process heap. This configuration is supported on Linux systems with cgroups and it's intended to be used in dynamic platforms like docker. This option is used to calculate memory_limit from the total available memory. For instance setting of 75% with the total memory of 1GiB will result in the limit of 750 MiB. The fixed memory setting (limit_mib) takes precedence over the percentage configuration.
• spike_limit_percentage (default = 20% of limit_percentage): Maximum spike expected between the measurements of memory usage. The value must be less than limit_percentage. This option is used to calculate spike_limit_mib from the total available memory. For instance setting of 25% with the total memory of 1GiB will result in the spike limit of 250MiB. This option is intended to be used only with limit_percentage.
• max_gc_interval_when_soft_limited (default = 30s): Caps the exponential backoff between forced GC calls while in soft-limited mode. When a forced GC fails to free memory, the interval doubles starting from min_gc_interval_when_soft_limited (or 95% of check_interval, whichever is larger) up to this cap. Resets to zero on effective GC or memory drop. Set to 0 to disable the backoff on this path; the path will then GC at intervals of min_gc_interval_when_soft_limited (which is every check interval if min is also 0).
• max_gc_interval_when_hard_limited (default = 30s): Same as above but for hard-limited mode. Set to 0 to disable.

Examples:

processors:
  memory_limiter:
    check_interval: 1s
    limit_mib: 4000
    spike_limit_mib: 800

• Hard limit will be set to 4000 MiB.
• Soft limit will be set to 4000 - 800 = 3200 MiB.

processors:
  memory_limiter:
    check_interval: 1s
    limit_percentage: 80
    spike_limit_percentage: 15

On a machine with 1000 MiB total memory available:

• Hard limit will be set to 1000 * 0.80 = 800 MiB.
• Soft limit will be set to 1000 * 0.80 - 1000 * 0.15 = 1000 * 0.65 = 650 MiB.

Documentation

Index

• func NewFactory() xprocessor.Factory
• type Config

Functions

func NewFactory

func NewFactory() xprocessor.Factory

NewFactory returns a new factory for the Memory Limiter processor.

Types

type Config

type Config = memorylimiter.Config