Johannes Schindelin wrote:
Hi,
On Mon, 14 Jul 2008, Andreas Ericsson wrote:
Sorry for being clueless here, but why does the older versions need
to be kept in-memory anyway? Aren't we applying the delta each time
we find one, repeatedly creating a new base-object in-memory for
each delta? If we aren't doing that, why do we need more than just
a small amount of memory just for keeping the delta?
Think of a delta chain of 49 delta objects, 1 base object. Now
reconstruct all of the objects.
If you do it one by one, not storing the intermediate results, you end up
applying 1 delta for the first, 2 for the second (first the first, then
the second), and so on, in total 1 + 2 + 3 + ... + 49 = 49 * 50 / 2 = 1225
times.
Compare that to the 49 times when reusing the intermediate results.
That's only true if you discard the result of applying D1 to DB though.
What I'm wondering is; Why isn't it done like this (pseudo-code):
while (delta = find_earlier_delta(sha1)) {
if (is_base_object(delta)) {
base_object = delta;
break;
}
push_delta(delta, patch_stack);
}
while (pop_delta(patch_stack))
apply_delta(base_object, delta);
where "apply_delta" replaces the base_object->blob with the delta
applied, releasing the previously used memory?
That way, you'll never use more memory than the largest ever size
of the object + 1 delta at a time and still not apply the delta
more than delta_chain_length-1 times.
--
Andreas Ericsson andreas.ericsson@xxxxxx
OP5 AB www.op5.se
Tel: +46 8-230225 Fax: +46 8-230231
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