Docs: Add troubleshooting content (#26871)

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* Update troubleshoot-dashboards.md

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docs/sources/troubleshooting/diagnostics.md

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+title = "Enable diagnostics"
+type = "docs"
+[menu.docs]
+weight = 200
++++
+
+# Enable diagnostics
+
+You can set up the `grafana-server` process to enable certain diagnostics when it starts. This can be helpful
+when investigating certain performance problems. It's *not* recommended to have these enabled by default.
+
+## Turn on profiling
+
+The `grafana-server` can be started with the arguments `-profile` to enable profiling and  `-profile-port` to override
+the default HTTP port (`6060`) where the `pprof` debugging endpoints are available, for example:
+
+```bash
+./grafana-server -profile -profile-port=8080
+```
+
+Note that `pprof` debugging endpoints are served on a different port than the Grafana HTTP server.
+
+You can configure or override profiling settings using environment variables:
+
+```bash
+export GF_DIAGNOSTICS_PROFILING_ENABLED=true
+export GF_DIAGNOSTICS_PROFILING_PORT=8080
+```
+
+Refer to [Go command pprof](https://golang.org/cmd/pprof/) for more information about how to collect and analyze profiling data.
+
+## Use tracing
+
+The `grafana-server` can be started with the arguments `-tracing` to enable tracing and `-tracing-file` to override the default trace file (`trace.out`) where trace result is written to. For example:
+
+```bash
+./grafana-server -tracing -tracing-file=/tmp/trace.out
+```
+
+You can configure or override profiling settings using environment variables:
+
+```bash
+export GF_DIAGNOSTICS_TRACING_ENABLED=true
+export GF_DIAGNOSTICS_TRACING_FILE=/tmp/trace.out
+```
+
+View the trace in a web browser (Go required to be installed):
+
+```bash
+go tool trace <trace file>
+2019/11/24 22:20:42 Parsing trace...
+2019/11/24 22:20:42 Splitting trace...
+2019/11/24 22:20:42 Opening browser. Trace viewer is listening on http://127.0.0.1:39735
+```
+
+See [Go command trace](https://golang.org/cmd/trace/) for more information about how to analyze trace files.