Frank Harper wrote [edited]:
> What I'm wondering, is why aren't people using RRDtool (round robin database).
> I'm not an RRD expert, but I think it's highly optimized for just this kind of
> time-series data...
Yes, it is. Its sole disadvantage, from what I've read and toyed
with MRTG, is that it keeps compacting data. You get all the measurements
for recent timestamps, plus averages for measurements further back,
with ever-increasing time-period. If that's what you need (like MRTG),
it's ideal. However, there are cases where you need *all* data kept,
in an ever-increasing database (more like a log :-).
On another note, clarifying what I've said about temporal databases,
I agree that simple timestamps are easily managed as keys. Once you
get to timeranges, though, things get complicated. In any case,
you have to implement the time primitives yourself.
For timestamps (e.g. ts1 and ts2), you only have a predicate:
earlier(ts1,ts2) ts1 < ts2
(well, and probably equal).
For timeranges (e.g. tr1), you have:
inside(ts1,tr1) (ts1 > tr1.start) AND (ts1 < tr1.end)
and primitives involving two timeranges, like:
inside(tr1,tr2) (tr1.start > tr2.start) AND (tr1.end < tr2.end)
but then of course you also have functions like timerange union, with
u.start = MAX(tr1.start, tr2.start) and u.end = MIN(tr1.end, tr2.end)
but there are also non-overlapping timeranges, and so on.
I'm not sure what database organization should be used to facilitate
operations like these.
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