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Syslog Performance Testing

bash script to generate test messages

For generic test against any or multiple servers that accept plain TCP or UDP, see: test_syslog.sh --help.

Note:

  • The final output provides an example query to use in elasticsearch to find events related to a test run.
  • It's potentially useful as a reliability test against an already loaded syslog service.
  • The use of the external call to date for each message limits it's applicability as a load generation script.

Comparative test scripts

The benchmark folder has scripts to test baseline performance with netcat, bash and rsyslog configurations to compare overheads, etc. What follows is a brief summary. For more detail, see [benchmark/README.md].

dummy syslog client and sever

Unlike test_syslog.sh, the scripts use environment variables (container friendly). The dummy_syslog_clients.sh generates messages more rapidly by only using date at the start and end of a pseudo-client's spool of messages. Still, due to being written in bash, the output performance isn't optimal.

There's intentional dummy output protocol choice of none which sets the output to /dev/null. So none of the messages generated get sent to the syslog server (100% failure rate of course). this allows measuring the overhead of starting and stopping the benchmark without receiving any messages.

While the rsyslog impstats module generates sufficient system metrics for rsyslog, the /usr/bin/time function was used to create an overall summary as complimentary information. Most notably, is was a fun exercise to compare rsyslog with a psudo-syslog server that simply directs netcat listener output to file (dummy_syslog_server.sh).

python script to parse syslog json output

benchmark/usr/local/bin/summarise_results_from_rsyslog_pstats_json_log.py can parse, count and add summary stats over multiple metrics produced by impstats JSON file output.

benchmark/usr/local/bin/flatten_and_compare_benchmark_results.py further processes the data gathered from multiple benchmark runs, flatten nested JSON into a .csv format, and reports a few comparative stats between benchmarks.

Performance impact of getting time with TZ unset

The timeloop folder contains a stand-alone benchmark used to inspect the impact of setting TZ and whether or not it impacted docker container system calls that obtained the time.

The results showed that failing to set TZ can negatively impact performance when C stdlib.h's locatime() function is used. However, it was found rsyslog used C POSIX sys/time.h's gettimeofday() instead which appears unaffected.

Note however, TZ was important for rsyslog correctly handling time zones (at lease so in prior versions of rsyslog placed in a container).

Rsyslog options

General queues

See: https://github.com/rsyslog/rsyslog/blob/d70e3365c9e51d65364934ff8473437459cb8274/runtime/queue.c#L1559 for the source code that sets the main queue defaults which should also match defaults to ruleset queues. Note it's as follows:

Option rsyslog default
type FixedArray
size 50000
dequeueBatchSize 1024
minDequeueBatchSize 0
minDequeueBatchSize.timeout 1
workerThreads 1
workerThreadMinimumMessages queue.size/queue.workerthreads

See the Dockerfile to note how the above defaults are increased.

Input specific

imptcp

TODO

Output specific

TODO

Linux kernel tunables to consider

TODO

Linux kernel options related to rsyslog config

Kernel option Kernel description RedHat default Related rsyslog module and option(s) Note
imptcp SocketBacklog
imptcp ProcessOnPoller
imptcp/imtcp flowControl
imptcp/imtcp/imrelp KeepAlive 
/proc/sys/net/core/somaxconn

Other options

/proc/sys/net/ipv4/tcp_max_syn_backlog
/proc/sys/net/core/rmem_max

Rsyslog related: TODO

https://github.com/rsyslog/rsyslog/issues/81
http://rsyslog-users.1305293.n2.nabble.com/TCP-Keep-Alive-use-cases-td7590143.html

Kernel related: TODO

https://vincent.bernat.ch/en/blog/2014-tcp-time-wait-state-linux
https://stackoverflow.com/questions/25503982/how-tcp-zero-window-can-be-detected-on-linux
https://eklitzke.org/how-tcp-sockets-work
http://veithen.io/2014/01/01/how-tcp-backlog-works-in-linux.html
https://perfchron.com/2015/12/26/investigating-linux-network-issues-with-netstat-and-nstat/
https://www.binarytides.com/linux-ss-command/
https://pracucci.com/linux-tcp-rto-min-max-and-tcp-retries2.html
https://access.redhat.com/solutions/893413

References