adding postgresql

postgresql/cli.md

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+### Get list of users and numbers of active connections
+
+```sql
+SELECT
+    datname AS database_name,
+    usename AS user_name,
+    count(*) AS active_connections
+FROM pg_stat_activity
+GROUP BY datname, usename order by active_connections DESC;
+```
+
+### Limit number of connections for user
+
+```sql
+alter user keycloak connection limit 80;ALTER ROLE
+```
+
+### Remove limit number of connections for user
+
+```sql
+alter user keycloak connection limit -1;ALTER ROLE
+```
+
+### Get replication status
+
+```sql
+select * from pg_stat_replication;
+```