brisbane:CHKMap.iteritems() tweaks

[Robert Collins]

On Wed, 2009-03-25 at 07:12 -0500, John Arbash Meinel wrote:
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> Robert Collins wrote:
> > On Tue, 2009-03-24 at 22:35 -0500, John Arbash Meinel wrote:
> >> So there is a significant amount of overhead in
> >> 'Access.get_raw_records', since we are reading 720*XMiB of compressed
> >> data, even though we only care about the first few bytes out of each
> >> block. And then there is a certain amount of overhead decompressing
> >> the
> >> extra 32KiB from each block (this seems to be trivial, as if I set the
> >> extra decompress size down to 0, it only seems to save 50ms)
> > 
> > Why are we reading more data than needed? (I thought I had code
> > [disabled] to read only the part of the compressed group needed.
> 
> We decompress only the bytes we need, but we don't have anything about
> how many compressed bytes we need.

Hmm, my original concept was to record:
pack_start
pack_end[of-needed-compressed-data]
decompressed_start
decompressed_end

precisely to allow that, I guess I didn't get to it :(.

-Rob
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