question about poker trackers

Just wondering if someone could explain what postgresql is, and how it works?
Also, do poker tracker and holdem manager use a players betting stats from just the current game or do they keep a history of all the players in a massive data base. Just wondering, any info would be appreciated,
Thanks

postgresql is simply a database format (as opposed to 'access'); it's better/faster for larger amounts of data with regard to tracking software.

PT/HEM only record hands that you (your player ID) have actually seen (which can become 'massive'). However, you can purchase hand history data which will add to your database and give you more information. This might be illegal according to the terms and conditions of certain sites, and has also been debated on a purely ethical level as well (not to get into either of those here...).