How to Report a Scylla Problem

In the event there is an issue you would like to report to ScyllaDB support, you need to submit logs and other files which help the support team diagnose the issue. Only the ScyllaDB support team members can read the data you share.

In general, there are two types of issues:

  • Scylla failure - There is some kind of failure, possibly due to a connectivity issue, a timeout, or otherwise, where the Scylla server or the Scylla nodes are not working. These cases require you to send ScyllaDB support both a Health Check Report as well as Core Dump files (if available).
  • Scylla performance - you have noticed some type of degradation of service with Scylla reads or writes. If it is clearly a performance case and not a failure, refer to Report a performance problem.

Once you have used our diagnostic tools to report the current status, you need to Send files to ScyllaDB support for further analysis.

Make sure the Scylla system logs are configured properly to report info level messages: install debug info.

Note

If you are unsure which reports need to be included, Open a support ticket or Git issue and consult with the ScyllaDB team.

Health Check Report

The Health Check Report is a script which generates:

  • An archive file (output_files.tgz) containing configuration data (hardware, OS, Scylla SW, etc.)
  • System logs
  • A Report file (<node_IP>-health-check-report.txt) based on the collected info.

If your node configuration is identical across the cluster, you only need to run the script once on one node. If not you will need to run the script on multiple nodes.

Prepare Health Check Report

Procedure:

  1. Run the node healthcheck:
$ node_health_check

The report generates output files. Once complete, a similar message is displayed:

Health Check Report Created Successfully
Path to Report: ./192.0.2.0-health-check-report.txt
  1. Follow the instructions in Send files to ScyllaDB support.

Core Dump

When Scylla fails, it creates core dump which can later be used to debug the issue. The file is written to /var/lib/scylla/coredump. If there is no file in the directory, see Troubleshooting Core Dump.

Compress the core dump file

Procedure

  1. The core dump file can be very large. Make sure to zip it using xz or similar.
xz -z core.21692
  1. Upload the compressed file to upload.scylladb.com. See Send files to ScyllaDB support.

Troubleshooting Core Dump

In the event the /var/lib/scylla/coredump directory is empty, the following solutions may help. Note that this section only handles some of the reasons why a core dump file is not created. It should be noted that in some cases where a core dump file fails to create not because it is in the wrong location or because the system is not configured to generate core dump files, but because the failure itself created an issue where the core dump file wasn’t created or is not accessible.

Operating System not set to generate core dump files

If Scylla restarts for some reason and there is no core dump file, the OS system deamon needs to be modified.

Procedure

  1. Open the custom configuration file. /etc/systemd/coredump.conf.d/custom.conf.
  2. Refer to generate core dumps for details.

Note: You will need a spare disk space which is larger than Scylla RAM.

Core dump file exists, but not where you expect it to be

If the scylla/coredump directory is empty even after you changed the custom configuration file, it might be that Automatic Bug Reporting Tool (ABRT) is running and all core dumps are pipelined directly to it.

Procedure

  1. Check the /proc/sys/kernel/core_pattern file. If it contains something similar to |/usr/libexec/abrt-hook-ccpp %s %c %p %u %g %t %h %e 636f726500 replace the contents with core.

Report a performance problem

If you are experiencing a performance issue when using Scylla, let us know and we can help. To save time and increase the likelihood of a speedy solution, it is important to supply us with as much information as possible.

Include the following information in your report:

Metrics Reports

There are two types of metrics you need to collect: Scylla Server and Scylla Client(node). The Scylla Server metrics can be displayed using an external monitoring service like Grafana or they can be collected using scyllatop and other commands.

Note

It is highly recommended to use the Scylla monitoring stack so that the Prometheus metrics collected can be shared.

Server Metrics

There are several commands you can use to see if there is a performance issue on the Scylla Server. Note that checking the CPU load using top is not a good metric for checking Scylla. Use scyllatop instead.

Note

To help ScyllaDB support assess your problem, it is best to pipe the results to a file which you can attach with the Health Check report.

  1. Check the Send files to ScyllaDB supportgauge-load. If the load is close to 100%, the bottleneck is Scylla CPU.
$ scyllatop *gauge-load
  1. Check if one of Scylla core is busier than the others:
$ sar -P ALL
  1. Check the load on one CPU (0 in this example)
$ perf top -C0
  1. Check if the disk utilization percentage is close to 100%. If yes, the disk might be the bottleneck.
$ ostat -x 1`` to observe the disk utilization.
  1. Collect run time statistics.
$ sudo perf record --call-graph dwarf -C 0 -F 99 -p $(ps -C scylla -o pid --no-headers) -g sleep 10

Alternatively, you can run the ``sudo ./collect-runtime-info.sh`` `source <https://gist.github.com/tzach/b2cf347a198e63939643a1af910b036e/>`_ which does all of the above, except scyllatop and upload the compressed result to s3. You can also see the results in `./report` dir

Server Metrics with Prometheus

When using Grafana and Prometheus to monitor Scylla, sharing the metrics stored in Prometheus is very useful. This procedure shows how to gather the metrics from the monitoring server.

Procedure

  1. Validate Prometheus instance is running
$ docker ps
  1. Download the DB, using your CONTAINER ID instead of a64bf3ba0b7f
$ sudo docker cp a64bf3ba0b7f:/prometheus /tmp/prometheus_data
  1. Zip the file.
sudo tar -zcvf /tmp/prometheus_data.tar.gz /tmp/prometheus_data/
  1. Upload the file you created in step 3 to upload.scylladb.com (see Send files to ScyllaDB support).

Client Metrics

Check the client CPU using top. If the CPU is close to 100%, the bottleneck is the client CPU. In this case, you should add more loaders to stress Scylla.

Send files to ScyllaDB support

Once you have collected and compressed your reports, send them to ScyllaDB for analysis.

Procedure

  1. Generate a UUID:
export report_uuid=$(uuidgen)
  1. Upload the report files:
curl -X PUT http://upload.scylladb.com/$report_uuid/yourfile -T yourfile

For example with the health check report and node health check report:

curl -X PUT http://upload.scylladb.com/$report_uuid/output_files.tgz -T output_files.tgz
curl -X PUT http://upload.scylladb.com/$report_uuid/192.0.2.0-health-check-report.txt -T 192.0.2.0-health-check-report.txt

The UUID you generated replaces the variable $report_uuid at runtime. yourfile is any file you need to send to ScyllaDB support.

Open a support ticket or Git issue

If you have not done so already, supply ScyllaDB support with the UUID. Keep in mind that although the ID you supply is public, only ScyllaDB support team members can read the data you share. In the ticket/issue you open, list the documents you have uploaded.

Procedure

  1. Do one of the following:
  • If you are a Scylla customer, open a Support Ticket and include the UUID within the ticket.
  • If you are a Scylla user, open an issue on GitHub and include the UUID within the issue.

See Also

Scylla benchmark results for an example of the level of details required in your reports.

Troubleshoot