Messages in this thread | | | Date | Thu, 12 May 2005 18:11:49 -0700 | From | Matt Mackall <> | Subject | Re: Mercurial 0.4e vs git network pull |
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On Thu, May 12, 2005 at 08:33:56PM -0400, Daniel Barkalow wrote: > On Thu, 12 May 2005, Matt Mackall wrote: > > > On Thu, May 12, 2005 at 05:24:27PM -0400, Daniel Barkalow wrote: > > > On Thu, 12 May 2005, Matt Mackall wrote: > > > > > > > Does this need an HTTP request (and round trip) per object? It appears > > > > to. That's 2200 requests/round trips for my 800 patch benchmark. > > > > > > It requires a request per object, but it should be possible (with > > > somewhat more complicated code) to overlap them such that it doesn't > > > require a serial round trip for each. Since the server is sending static > > > files, the overhead for each should be minimal. > > > > It's not minimal. The size of an HTTP request is often not much > > different than the size of a compressed file delta. > > I was thinking of server-side processing overhead, not bandwidth. It's > true that the bandwidth could be noticeable for these small files. > > > All the junk that gets bundled in an http request/response will be > > similar in size to the stuff in the third column. > > kernel.org seems to send 283-byte responses, to be completely > precise. This could be cut down substantially if Apache were tweaked a bit > to skip all the optional headers which are useless or wrong in this > context. (E.g., that includes sending a content-type of "text/plain" for > the binary data) > > > Does it do this recursively? Eg, if the server has 800 new linear > > commits, does the client have to do 800 round trips following parent > > pointers to find all the new changesets? > > Yes, although that also includes pulling the commits, and may be > interleaved with pulling the trees and objects to cover the > latency. (I.e., one round trip gets the new head hash; the second gets > that commit; on the third the tree and the parent(s) can be requested at > once; on the fouth the contents of the tree and the grandparents, at > which point the bandwidth will probably be the limiting factor for the > rest of the operation.)
What if a changeset is smaller than the bandwidth-delay product of your link? As an extreme example, Mercurial is currently at a point where its -entire repo- changegroup (set of all changesets) can be in flight on the wire on a typical link.
> > In this case, Mercurial does about 6 round trips, totalling less than > > 1K, plus one requests that pulls everything. > > I must be misunderstanding your numbers, because 6 HTTP responses is more > than 1K, ignoring any actual content from the server, and 1K for 800 > commits is less than 2 bytes per commit.
1k of application-level data, sorry. And my whole point is that I don't send those 800 commit identifiers (which are 40 bytes each as hex). I send about 30 or so. It's basically a negotiation to find the earliest commits not known to the client with a minimum of round trips and data exchange.
> I'm also worried about testing on 800 linear commits, since the projects > under consideration tend to have very non-linear histories.
Not true at all. Dumps from Andrew to Linus via patch bombs will result in runs of hundreds of linear commits on a regular basis. Linear patch series are the preferred way to make changes and series of 30 or 40 small patches are not at all uncommon.
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