Issue

Views on Tableau Server eventually fail to load.  This may also result in a 502 error after approximately 30 minutes.

Checking the vizqlserver logs will show the log entries with the action begin-vql-session-save-workbook-for-checkpoint as the final entry for an Apache request id. 

The Apache request id in the following example is XFRVQc82Wz2e6RrSxr@vpwAAAOU:

{"ts":"2019-02-01T14:18:42.009","pid":7436,"tid":"f484","sev":"info","req":"XFRVQc82Wz2e6RrSxr@vpwAAAOU","sess":"BE8A7BF9510B4ED187819C5F5C73DAEA-1:3","k":"begin-vql-session-checkpoint-workbook-xml","l":{},"a":{"depth":4,"id":"K11HZQm4UYdJwFo1JL4AOk","name":"vql-session-checkpoint-workbook-xml","root":"Ohu1ryXYE43I8hqZP8jrxe","sponsor":"C4gSIVGcUXKJkX7XDPenNn"}
{"ts":"2019-02-01T14:18:42.009","pid":7436,"tid":"f484","sev":"info","req":"XFRVQc82Wz2e6RrSxr@vpwAAAOU","sess":"BE8A7BF9510B4ED187819C5F5C73DAEA-1:3","k":"begin-vql-session-save-workbook-for-checkpoint","l":{},"a":{"depth":5,"id":"GIUZ6mgjUT0JfWTQ4Sdnd5","name":"vql-session-save-workbook-for-checkpoint","root":"Ohu1ryXYE43I8hqZP8jrxe","sponsor":"K11HZQm4UYdJwFo1JL4AOk"}