[Gllug] Introductions to Databases

[Richard Huxton]

Chris Bell wrote:
> On Tue 14 Jul, Richard Jones wrote:
> 
>> That leaves you with PostgreSQL, which is an excellent relational
>> database *and* comes with copious online documentation, both a
>> tutorial and detailed technical docs:
>>
>>   http://www.postgresql.org/docs/8.4/static/index.html

Also worth either borrowing from your library, or getting second-hand 
is: "An Introduction to Database Systems" - C.J. Date

It's probably the standard academic introduction to relational database 
theory.

>    Can PostgreSQL do anything like continuous live backup to another
> machine? I am thinking of a condition where a company relies on cotinuous
> access to its database, covering all company activities, and everything
> would stop if one machine dies until a replacement can be brought on line.

Yes, it's called Point-in-time-recovery (PITR) and involves shipping the 
transaction logs to the remote machine which replays them exactly as 
though it's recovering from a power failure. The nice thing about this 
is that it's exercising exactly the code you want to work reliably in 
the event of an actual power failure.

The bad news is that it's currently more fiddly than strictly necessary 
if you want e.g. no more than a 1 second lag between the two machines. 
The other problem is that the second machine is strictly a backup system 
- you can't run queries against it. The good news is that synchronous 
replication and hot standby patches are around and almost certain to be 
in 8.5 (they were submitted to 8.4 but weren't quite ready in time).

-- 
   Richard Huxton
   Archonet Ltd
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