Re: [Monotone-devel] speed of "mtn ls branches"

[Thomas Moschny]

On Thursday 17 January 2008 Nathaniel Smith wrote:
> If one really does want to get 'ls branches' exactly correct in that
> case, the right way isn't to do expensive head-calculation anyway.
> All we need to know is that there is some valid branch cert out there
> somewhere, and we can tell that by just pulling a cert out of the db
> and checking it, which is very cheap.

As far as I remember, that's not quite correct. You'd need to validate at 
least one cert per branch (and even more, if some certs happen to be 
invalid). That currently makes about 200 checks for the monotone.ca database. 
And cert validation is expensive. That's exactly why we came up with the idea 
of interleaving ancestor elimination and cert validation (erase ancestors and  
failures) for the heads code a while ago, which significantly sped up things.

- Thomas

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