Add Diagnose Problems In A Heroku Postgres Database as a Heroku til

README.md

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@@ -339,6 +339,7 @@ _1187 TILs and counting..._
 ### Heroku
 
 - [Deploy A Review App To A Different Stack](heroku/deploy-a-review-app-to-a-different-stack.md)
+- [Diagnose Problems In A Heroku Postgres Database](heroku/diagnose-problems-in-a-heroku-postgres-database.md)
 - [Set And Show Heroku Env Variables](heroku/set-and-show-heroku-env-variables.md)
 - [SSH Into Heroku Server Hosting App](heroku/ssh-into-heroku-server-hosting-app.md)
 

heroku/diagnose-problems-in-a-heroku-postgres-database.md

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+# Diagnose Problems In A Heroku Postgres Database
+
+Heroku keeps track of all kinds of diagnostics on the performance of your app's
+database. From long running queries and transactions to index cache hit rates
+to unused indexes to tables with bloat.
+
+Running the `pg:diagnose` command for your Heroku app will surface all of these
+details in the terminal.
+
+```bash
+$ heroku pg:diagnose -a APP_NAME
+```
+
+The report will start with the biggest problem areas which it color codes in
+red. If your app is experiencing degraded performance, the list of red items
+would be a good place to start investigating.
+
+The report will then list less urgent problem areas. Those will be color coded
+yellow. Though Heroku has deemed these less serious, you may still want to deal
+with these.
+
+All the other areas of diagnose will fall into the _green_ bucket. Meaning
+Heroku doesn't see any issues in those areas.