[PATCH 1 of 4 lazy-manifest v2] manifest.c: new extension code to lazily parse manifests

[Augie Fackler]

On Jan 13, 2015, at 9:35 PM, Martin von Zweigbergk <martinvonz at google.com> wrote:

> If updates are in bulk without queries in between, it should be possible to just append the updates to the list. Then, on query, sort with a stable sort, pick the last entry for each file and drop the rest. Makes sense?

Yes, but how do we tell if the code is doing something like

m[‘foo’] = node1
m[‘foo’] = node2

which would fail if we inserted ‘foo’ on the first call and then didn’t manage to realize we already had an (unsorted) line for foo, but still appears to be just insertions.

If we have a bulk-insert code path, we can avoid that part of the problem.

> 
> If queries are interleaved, we would have a problem anyway and would have to do something smarter.
> 
> 
> On Tue, Jan 13, 2015, 18:24 Augie Fackler <raf at durin42.com> wrote:
> 
> On Jan 13, 2015, at 9:22 PM, Martin von Zweigbergk <martinvonz at google.com> wrote:
> 
> >
> >
> > On Tue, Jan 13, 2015, 18:11 Augie Fackler <raf at durin42.com> wrote:
> >
> >
> > On Jan 13, 2015, at 7:42 PM, Martin von Zweigbergk <martinvonz at google.com> wrote:
> >
> > > As I reported on IRC, the 'setitem' method seems slow. On the Mozilla repo, running
> > >
> > >   hg co -C 1813b && hg mv -q intl i18n && time hg ci -qm 'move intl'
> > >
> > > takes 6.3s with current hg and 1m21s with these patches applied. It may very be related to your TODO in setitem.
> >
> > Yeah, I think this is the point where we should drop v2, and I’ll work on a bulk-add function (shouldn’t take long) to mitigate that problem.
> >
> >
> >
> > I think I once suggested making it transparent to the user by instead storing modifications separately and then compacting them on any query operation. That should effectively be the same (performance-wise) as an explicit bulk update operation, but without the need to update any callers.
> 
> But if someone inserts a new entry, then does it again, the binary search won’t work, which makes things frustrating. If you’ve got an idea for that, I’d love to hear it though (I haven’t come up with anything better.)
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