Consider history like this:
o
| o
| |
| o
| |
| o
|/
o
| o
| |
| o
| |
| o
|/
o
| o
| |
| o
| |
| o
|/
o
~
Assume the left mainline is available in the remote repo and the other
commits are only in the local repo. Also imagine that instead of 3
local branches with 3 commits on each, there are 1000 branches (the
number of commits on each doesn't matter much here). In such a
scenario, the current setdiscovery code will pick a sample size of 200
among these branches and ask the remote which of them it has. However,
the discovery for each such branch is completely independent of the
discovery for the others -- knowing whether the remote has a commit in
one branch doesn't give us any information about the other
branches. The discovery will therefore take at least 5 roundtrips
(maybe more depending on which commit in each linear chain was
sampled). Since the discovery for each branch is independent, there is
no reason to let one branch wait for another, so this patch makes it
so we sample at least as many commits as there are branches (called
"connecteds" in the code). It may still happen (it's very likely,
even) that we get multiple samples from one branch and none from
another, but that will even out over a few rounds and I think this is
still a big improvement.
Because of http header size limits, we still use the old behavior
unless experimental.httppostargs=true.
I've timed this by running `hg debugdiscovery mozilla-unified --debug` in the
mozilla-try repo. Both repos were local. Before this patch, last part
of the output was:
2249 total queries in 5276.4859s
elapsed time: 5276.652634 seconds
heads summary:
total common heads: 13
also local heads: 4
also remote heads: 8
both: 4
local heads: 28317
common: 4
missing: 28313
remote heads: 12
common: 8
unknown: 4
local changesets: 2014901
common: 530373
missing: 1484528
common heads: 1dad417c28ad 4a108e94d3e2 4d7ef530fffb 5350524bb654 777e60ca8853 7d97fafba271 9cd2ab4d0029 a55ce37217da d38398e5144e dcc6d7a0dc00 e09297892ada e24ec6070d7b fd559328eaf3
After this patch, the output was (including all the samples, since
there were so few now):
query 1; heads
searching for changes
taking initial sample
query 2; still undecided: 1599476, sample size is: 22604
sampling from both directions
query 3; still undecided: 1051104, sample size is: 314035
sampling from both directions
query 4; still undecided: 301690, sample size is: 151416
sampling from both directions
query 5; still undecided: 87581, sample size is: 65140
sampling from both directions
query 6; still undecided: 17166, sample size is: 16019
sampling from both directions
query 7; still undecided: 1066, sample size is: 1064
sampling from both directions
query 8; still undecided: 2, sample size is: 2
8 total queries in 24.0865s
elapsed time: 24.247765 seconds
heads summary:
total common heads: 13
also local heads: 4
also remote heads: 8
both: 4
local heads: 28317
common: 4
missing: 28313
remote heads: 12
common: 8
unknown: 4
local changesets: 2014901
common: 530373
missing: 1484528
2249 total queries in 5276.4859s
elapsed time: 5276.652634 seconds
heads summary:
total common heads: 13
also local heads: 4
also remote heads: 8
both: 4
local heads: 28317
common: 4
missing: 28313
remote heads: 12
common: 8
unknown: 4
local changesets: 2014901
common: 530373
missing: 1484528
common heads: 1dad417c28ad 4a108e94d3e2 4d7ef530fffb 5350524bb654 777e60ca8853 7d97fafba271 9cd2ab4d0029 a55ce37217da d38398e5144e dcc6d7a0dc00 e09297892ada e24ec6070d7b fd559328eaf3
After this patch, the output was (including all the samples, since
there were so few now):
query 1; heads
searching for changes
taking initial sample
query 2; still undecided: 1599476, sample size is: 22604
sampling from both directions
query 3; still undecided: 1051104, sample size is: 314035
sampling from both directions
query 4; still undecided: 301690, sample size is: 151416
sampling from both directions
query 5; still undecided: 87581, sample size is: 65140
sampling from both directions
query 6; still undecided: 17166, sample size is: 16019
sampling from both directions
query 7; still undecided: 1066, sample size is: 1064
sampling from both directions
query 8; still undecided: 2, sample size is: 2
8 total queries in 24.0865s
elapsed time: 24.247765 seconds
heads summary:
total common heads: 13
also local heads: 4
also remote heads: 8
both: 4
local heads: 28317
common: 4
missing: 28313
remote heads: 12
common: 8
unknown: 4
local changesets: 2014901
common: 530373
missing: 1484528
common heads: 1dad417c28ad 4a108e94d3e2 4d7ef530fffb 5350524bb654 777e60ca8853 7d97fafba271 9cd2ab4d0029 a55ce37217da d38398e5144e dcc6d7a0dc00 e09297892ada e24ec6070d7b fd559328eaf3