Why is querying SVV_TABLE_INFO so slow?

i would start with understanding the workload on the cluster when you are trying to execute the query use the following query to see what running queries are currently active; select user_name, db_name, starttime, pid, replace(trim(query),'\n',' ') from stv_recents where status = 'Running' order by starttime;

As mentioned in the other answer the best place to start is to monitor the cluster performance at the time you are experiencing issues. Aside from the query above, you could look at the different steps described in the documentation section dedicated to "Monitoring Amazon Redshift cluster performance".

hope this helps