Confluence diagnostics: sandbox crashed or was terminated during document conversion

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This diagnostic alert only applies to sites with a Confluence Data Center license.

It is disabled by default, as it may have a performance impact on your site. Our support team may ask you to enable this alert when troubleshooting a specific problem.

This diagnostic alert warns you when a document conversion sandbox has crashed or was terminated during conversion. For a full explanation of how Confluence Data Center handles document conversion in a sandbox, head to Document conversion for Confluence Data Center

The following appears in the application log:

INFO ; SANDBOX ; SANDBOX-2001 ; A sandbox process has been killed ; not-detected ;  ;  ; {"username":"...","fileName":"...","fileFormat":"...","conversionType":"...","fileSize":...,"actualTimeInSecs":...,"timeLimitInSecs":...,"memoryLimitInMegabytes":...}

To resolve this issue

The idea behind the document conversion sandbox is that it can crash or be terminated without impacting Confluence. We expect that the sandbox will be terminated occasionally, for example when it's unable to process an extremely large or complex file in time, however if you're seeing a lot of failures it's worth investigating further. 

To decrease the likelihood of a crash or termination:

  • make sure there is enough free memory on each node for the sandboxes. We recommend 2GB per node, for two sandboxes. You'll need more memory if you have more sandboxes.
  • increase the timeout threshold (using the -Ddocument.conversion.sandbox.request.time.limit.secs system property). This can be useful if you know users are regularly uploading large or very complex files. 
  • increase the number of sandboxes (using the -Dconversion.sandbox.pool.size system property). If you significantly increase the time limit, you may also want to add more sandboxes so you can process more files in parallel. 
  • make sure the sandbox settings are the same on each node, and that every node has adequate memory and disk space. It may be that problems are occurring on just one node.

The system property -Dconversion.sandbox.pool.size was renamed in Confluence 6.12.

When running Confluence 6.11 or lower, this property is named -Ddocument.conversion.sandbox.pool.size, respectively.

What will happen if I ignore this alert? 

If the sandbox does not have enough memory to complete document conversion for the uploaded file, or the process times out, thumbnail generation will fail. A placeholder thumbnail will be used on the page, and a download option will be provided in the file preview. Confluence does not re-attempt to generate thumbnails for a failed attachment, and re-inserting the attached file into the editor will not trigger the process. 

An occasional failure, for extremely large or complex files, is expected, but the end user experience will be severely impacted if document conversion is failing on a regular basis. 

Can I change the alert threshold? 

This diagnostic alert is not configurable. 

The behaviour of the sandbox is configurable however, see Document conversion for Confluence Data Center for more information. 

Last modified on Apr 19, 2021

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