Until now PBXT has been ACId (with a lower-case d). This is soon
to change as I have had some weeks to work on a fully durable
version of the transactional engine (http://www.primebase.com/xt).
My first concern in making PBXT fully durable was to what extent
I would have to abandon the original "write-once" design. While
there are a number of ways to implement durability, the only
method used by databases (as far as I know) is the write-ahead
log.
The obvious advantage of this method is that all changes can be
flushed at once. However, this requires that all data be written
twice: once to the log and after that, to the database
itself.
My solution to this problem is a compromise, but I think it is a
good one. In a nutshell: short records are written twice, and
long records are written once. When it comes to durability, this
compromise, I …
Dec
20
2007