Columnar Databases Performance Characteristics Discussions

A discussion detailing performance characteristics of columnar databases, and what situations they are better and what situations they are not.

https://news.ycombinator.com/item?id=3524437

Postgres Query for Current Running Queries

In short, query the pg_stat_activity table

Reference: http://chrismiles.info/systemsadmin/databases/articles/viewing-current-postgresql-queries/

JSch Error "com.jcraft.jsch.JSchException: reject HostKey" Even After Host Key Has Been Added

Usually when this error happens, all you need to do is to add the host key in a normal SSH session. However, this can also happen when the host key is in a format that JSch does not recognise or support e.g. I had a problem with a "ecdsa-sha2-nistp256" encoded host key.

To fix this I had to use the "ssh-keyscan -t rsa <hostname>" command (on the server) to obtain the host key in rsa format and then I manually added that to the "known_hosts" file.

Reference: http://anahorny.blogspot.sg/2013/05/solution-for-comjcraftjschjschexception.html