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discovery: slowly increase sampling size...
discovery: slowly increase sampling size Some pathological discovery runs can requires many roundtrip. When this happens things can get very slow. To make the algorithm more resilience again such pathological case. We slowly increase the sample size with each roundtrip (+5%). This will have a negligible impact on "normal" discovery with few roundtrips, but a large positive impact of case with many roundtrips. Asking more question per roundtrip helps to reduce the undecided set faster. Instead of reducing the undecided set a linear speed (in the worst case), we reduce it as a guaranteed (small) exponential rate. The data below show this slow ramp up in sample size: round trip | 1 | 5 | 10 | 20 | 50 | 100 | 130 | sample size | 200 | 254 | 321 | 517 | 2 199 | 25 123 | 108 549 | covered nodes | 200 | 1 357 | 2 821 | 7 031 | 42 658 | 524 530 | 2 276 755 | To be a bit more concrete, lets take a very pathological case as an example. We are doing discovery from a copy of Mozilla-try to a more recent version of mozilla-unified. Mozilla-unified heads are unknown to the mozilla-try repo and there are over 1 million "missing" changesets. (the discovery is "local" to avoid network interference) Without this change, the discovery: - last 1858 seconds (31 minutes), - does 1700 round trip, - asking about 340 000 nodes. With this change, the discovery: - last 218 seconds (3 minutes, 38 seconds a -88% improvement), - does 94 round trip (-94%), - asking about 344 211 nodes (+1%). Of course, this is an extreme case (and 3 minutes is still slow). However this give a good example of how this sample size increase act as a safety net catching any bad situations. We could image a steeper increase than 5%. For example 10% would give the following number: round trip | 1 | 5 | 10 | 20 | 50 | 75 | 100 | sample size | 200 | 321 | 514 | 1 326 | 23 060 | 249 812 | 2 706 594 | covered nodes | 200 | 1 541 | 3 690 | 12 671 | 251 871 | 2 746 254 | 29 770 966 | In parallel, it is useful to understand these pathological cases and improve them. However the current change provides a general purpose safety net to smooth the impact of pathological cases. To avoid issue with older http server, the increase in sample size only occurs if the protocol has not limit on command argument size.

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urls.txt
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Valid URLs are of the form::
local/filesystem/path[#revision]
file://local/filesystem/path[#revision]
http://[user[:pass]@]host[:port]/[path][#revision]
https://[user[:pass]@]host[:port]/[path][#revision]
ssh://[user@]host[:port]/[path][#revision]
Paths in the local filesystem can either point to Mercurial
repositories or to bundle files (as created by :hg:`bundle` or
:hg:`incoming --bundle`). See also :hg:`help paths`.
An optional identifier after # indicates a particular branch, tag, or
changeset to use from the remote repository. See also :hg:`help
revisions`.
Some features, such as pushing to http:// and https:// URLs are only
possible if the feature is explicitly enabled on the remote Mercurial
server.
Note that the security of HTTPS URLs depends on proper configuration of
web.cacerts.
Some notes about using SSH with Mercurial:
- SSH requires an accessible shell account on the destination machine
and a copy of hg in the remote path or specified with remotecmd.
- path is relative to the remote user's home directory by default. Use
an extra slash at the start of a path to specify an absolute path::
ssh://example.com//tmp/repository
- Mercurial doesn't use its own compression via SSH; the right thing
to do is to configure it in your ~/.ssh/config, e.g.::
Host *.mylocalnetwork.example.com
Compression no
Host *
Compression yes
Alternatively specify "ssh -C" as your ssh command in your
configuration file or with the --ssh command line option.
These URLs can all be stored in your configuration file with path
aliases under the [paths] section like so::
[paths]
alias1 = URL1
alias2 = URL2
...
You can then use the alias for any command that uses a URL (for
example :hg:`pull alias1` will be treated as :hg:`pull URL1`).
Two path aliases are special because they are used as defaults when
you do not provide the URL to a command:
default:
When you create a repository with hg clone, the clone command saves
the location of the source repository as the new repository's
'default' path. This is then used when you omit path from push- and
pull-like commands (including incoming and outgoing).
default-push:
The push command will look for a path named 'default-push', and
prefer it over 'default' if both are defined.