[opendemo-devel] file format

[Conor D. <co...@ma...>]

Hello all,

I think we should consider changing the file format as follows to speed up
playback, use much less memory, and simplify things:
- Record only one map per xml file, with each xml possilbly including a
reference to the next demo. We really need to do this if we want to allow
rewinding of demos during playback, since we can't store demos in memory. I
don't see how this hurts functionality.
- Get rid of the 16 states used for delta encoding, and force delta'ing only
from the previous snapshot (or baselines). This reduces the size of the od
struct by about 9 megs, and should completely remove the odpStartElement
performance bottleneck. We can keep the "currentSeq" and "deltaSeq" xml
attributes, just in case.
- Maybe move element data into attributes? E.g instead of:
    <currentOrigin index="0">586.87023</currentOrigin>
    we could use:
    <currentOrigin index="0" value="586.87023" />
I say this because AFAIK there is less variation allowed for attributes than
character data. For example, I think leading and trailing whitespace must
always be removed from attributes, while character data may or may not need
that whitespace (depending on the DTD). Since we don't use a validating XML
parser to handle these variances, maybe we should move to attributes?

-Conor