Add Prevent A Query From Running Too Long as a postgres til

postgres/prevent-a-query-from-running-too-long.md

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+# Prevent A Query From Running Too Long
+
+A number of different factors can effect how long a query takes to run.
+Certainly the size of a table and the complexity of the query play a big role.
+Locking can really slow a query down by making it wait to get started. A series
+of competing queries that induce table locking can grind things to a halt.
+
+If you don't want queries in a particular connection being allowed to wait or
+run too long, you can set a timeout.
+
+```sql
+set statement_timeout to '500';
+```
+
+That will ensure that any statement run in that connection will be terminated
+if it takes longer than 500ms.
+
+You can also specify a unit:
+
+```sql
+set statement_timeout to '15s';
+```
+
+That will enforce statement timeout of 15 seconds.
+
+See the
+[docs](https://www.postgresql.org/docs/current/runtime-config-client.html) for
+more details.