This article describes how to optimize Fluentd performance within a single process. If your traffic is up to 5,000 messages/sec, the following techniques should be enough.
With more traffic, Fluentd tends to be more CPU bound. In this case, consider using
Follow the Pre-installation Guide to configure your OS properly. This can drastically improve performance, and prevent many unnecessary problems.
If Fluentd does not perform well as expected, check with the
top command first. Try to identify which part of your system is becoming a bottleneck (CPU, Memory, Disk I/O, etc.).
This is a general recommendation. It is suggested NOT TO HAVE extra computations inside Fluentd. Fluentd is flexible to do quite a bit internally, but adding too much logic to configuration file makes it difficult to read and maintain while making it less robust. The configuration file should be as simple as possible.
If the destination of your logs is remote storage or service, adding a
flush_thread_count option will parallelize your outputs (the default is 1). Using multiple threads can hide the IO/network latency. This parameter is available for all output plugins.
<match test>@type output_plugin<buffer ...>flush_thread_count 8# ...</buffer># ...</match>
Note that this option does not improve the processing performance e.g. numerical computation, mutating record, etc.
Ruby has GIL (Global Interpreter Lock), which allows only one thread to execute at a time. While I/O tasks can be multiplexed, CPU-intensive tasks will block other jobs. One of the CPU-intensive tasks in Fluentd is compression.
The S3/Treasure Data plugin allows compression outside of the Fluentd process, using
gzip. This frees up the Ruby interpreter while allowing Fluentd to process other tasks.
# S3<match ...>@type s3store_as gzip_command<buffer ...>flush_thread_count 8# ...</buffer># ...</match># Treasure Data<match ...>@type tdloguse_gzip_command<buffer ...>flush_thread_count 8# ...</buffer># ...</match>
While not a perfect solution to leverage multiple CPU cores, this can be effective for most Fluentd deployments. As before, you can run this with
flush_thread_count option as well.
Ruby has several GC parameters to tune GC performance and you can configure these parameters via an environment variable (Parameter list). To reduce memory usage, set
RUBY_GC_HEAP_OLDOBJECT_LIMIT_FACTOR to a lower value.
RUBY_GC_HEAP_OLDOBJECT_LIMIT_FACTOR is used for full GC trigger and the default is
Here's a quote from the documentation:
Do full GC when the number of old objects is more than R * Nwhere R is this factor andN is the number of old objects just after last full GC.
So, the default GC behavior does not call full GC until the number of old objects reaches
2.0 * before old objects. This improves the throughput but it grows the total memory usage. This setting is not good for the low resource environment e.g. a small container. For such cases, try
See Ruby 2.1 Garbage Collection: ready for production and Watching and Understanding the Ruby 2.1 Garbage Collector at Work articles for more detail.
The CPU is often the bottleneck for Fluentd instances that handle billions of incoming records. To utilize multiple CPU cores, we recommend using the
multi workers feature.
For more details on this feature, please read multi process workers article.
If this article is incorrect or outdated, or omits critical information, please let us know. Fluentd is an open-source project under Cloud Native Computing Foundation (CNCF). All components are available under the Apache 2 License.