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Set JVM properties on start-up to increase the heap memory (at least 4GB) and change the garbage collectorand disable explicit garbage collection.

For Virtualizecli:

virtualizecli.sh -startServer -data <WORKSPACE_LOCATION> -J-Xms2048m -J-Xmx4096m -J-server -J-XX:+DisableExplicitGC

...

It is recommended to minimize the network latency between a Virtualize server and a Data Repository server as much as possible. Network latency between the processes can negatively impact the performance of the Virtualize server under load, and the most common way users accomplish this is by installing them on the same machine, or two machines that are co-located as much as possible (for example, same data center region). The Data Repository server can consume a large amount of memory, so when installing it on the same machine as a Virtualize server, it is advised that the machine have at least 32GB RAM (see デプロイメントの推奨事項 Deployment Recommendations).

Debugging Checklist 

1. Turn off performance profiles and additional delays in your Virtual assets.
2. Is the issue related to a specific asset? Are other assets performing like before?
3. If you have any responders or data source rows that are unused, can they be disabled or removed completely?
4. Check for any scripts that might be in the asset. If they are disabled, does the issue go away?
5. Are there any Network share drives hosting artifacts?
6. Does the issue reproduce with the same conditions on another server?