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If you experience a slow TeamCity web UI response, checking for changes process, server-side sources checkout, long cleanup times or other slow server activity, your target should be the machine where the TeamCity server is installed.
If the issue is related only to a single build, you will need to also investigate the TeamCity agent machine which is running the build.
Investigate the system resources (CPU, memory, IO) load. If there is a high load, determine the process to causing it. If it is not a TeamCity-related process, that might need addressing outside of the TeamCity scope.
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