brisbane:CHKMap.iteritems() tweaks

[John Arbash Meinel]

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Ian Clatworthy wrote:
> John Arbash Meinel wrote:
>>> 1) Change 'bzr pack' so that it creates a separate set of groups for
>>> items that are available in the newest XX (say 100) revisions. Or
>>> possibly group everything into 100 rev chunks.
>> This was easy to implement for CHK streams. And it changes "time bzr ls
>> -r-1" from 4.4s down to 1.6s. (I implemented as splitting at 10
>> revisions). And the time without the patch is 2.2s up from 1.6s. So the
>> patch makes a bigger difference when we aren't swamped with extract time.
> 
> Nice.
> 
>> The total size on disk after packing is barely noticeable:
>>  125666
>>  125981
>>
>> I guess that is 300KiB. But out of 125MiB, that is only 0.2%.
> 
> Well worth it IMO.

So the questions just become "what is a reasonable horizon" to use for
this. I can set it to 10 revs, 100 revs, etc. Do we want to do the same
thing for referenced texts? (I think we do.)

Going a bit further, it might make a good demarcation for using lzma
versus zlib. Or at least something like it. (0-100 packed separately,
100-1000 another zlib pack, 1000+ packed in lzma.) Of course, I'm sure
every project has a different numbers for "active, semi-active,
so-old-it-never-gets-touched".

John
=:->

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