view tests/test-setdiscovery.t @ 42354:dbd0fcca6dfc

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.

Function to test discovery between two repos in both directions, using both the local shortcut
(which is currently not activated by default) and the full remotable protocol:

  $ testdesc() { # revs_a, revs_b, dagdesc
  >     if [ -d foo ]; then rm -rf foo; fi
  >     hg init foo
  >     cd foo
  >     hg debugbuilddag "$3"
  >     hg clone . a $1 --quiet
  >     hg clone . b $2 --quiet
  >     echo
  >     echo "% -- a -> b tree"
  >     hg -R a debugdiscovery b --verbose --old
  >     echo
  >     echo "% -- a -> b set"
  >     hg -R a debugdiscovery b --verbose --debug --config progress.debug=true
  >     echo
  >     echo "% -- a -> b set (tip only)"
  >     hg -R a debugdiscovery b --verbose --debug --config progress.debug=true --rev tip
  >     echo
  >     echo "% -- b -> a tree"
  >     hg -R b debugdiscovery a --verbose --old
  >     echo
  >     echo "% -- b -> a set"
  >     hg -R b debugdiscovery a --verbose --debug --config progress.debug=true
  >     echo
  >     echo "% -- b -> a set (tip only)"
  >     hg -R b debugdiscovery a --verbose --debug --config progress.debug=true --rev tip
  >     cd ..
  > }


Small superset:

  $ testdesc '-ra1 -ra2' '-rb1 -rb2 -rb3' '
  > +2:f +1:a1:b1
  > <f +4 :a2
  > +5 :b2
  > <f +3 :b3'
  
  % -- a -> b tree
  comparing with b
  searching for changes
  unpruned common: 01241442b3c2 66f7d451a68b b5714e113bc0
  elapsed time:  * seconds (glob)
  heads summary:
    total common heads:          2
      also local heads:          2
      also remote heads:         1
      both:                      1
    local heads:                 2
      common:                    2
      missing:                   0
    remote heads:                3
      common:                    1
      unknown:                   2
  local changesets:              7
    common:                      7
    missing:                     0
  common heads: 01241442b3c2 b5714e113bc0
  
  % -- a -> b set
  comparing with b
  query 1; heads
  searching for changes
  all local heads known remotely
  elapsed time:  * seconds (glob)
  heads summary:
    total common heads:          2
      also local heads:          2
      also remote heads:         1
      both:                      1
    local heads:                 2
      common:                    2
      missing:                   0
    remote heads:                3
      common:                    1
      unknown:                   2
  local changesets:              7
    common:                      7
    missing:                     0
  common heads: 01241442b3c2 b5714e113bc0
  
  % -- a -> b set (tip only)
  comparing with b
  query 1; heads
  searching for changes
  all local heads known remotely
  elapsed time:  * seconds (glob)
  heads summary:
    total common heads:          1
      also local heads:          1
      also remote heads:         0
      both:                      0
    local heads:                 2
      common:                    1
      missing:                   1
    remote heads:                3
      common:                    0
      unknown:                   3
  local changesets:              7
    common:                      6
    missing:                     1
  common heads: b5714e113bc0
  
  % -- b -> a tree
  comparing with a
  searching for changes
  unpruned common: 01241442b3c2 b5714e113bc0
  elapsed time:  * seconds (glob)
  heads summary:
    total common heads:          2
      also local heads:          1
      also remote heads:         2
      both:                      1
    local heads:                 3
      common:                    1
      missing:                   2
    remote heads:                2
      common:                    2
      unknown:                   0
  local changesets:             15
    common:                      7
    missing:                     8
  common heads: 01241442b3c2 b5714e113bc0
  
  % -- b -> a set
  comparing with a
  query 1; heads
  searching for changes
  all remote heads known locally
  elapsed time:  * seconds (glob)
  heads summary:
    total common heads:          2
      also local heads:          1
      also remote heads:         2
      both:                      1
    local heads:                 3
      common:                    1
      missing:                   2
    remote heads:                2
      common:                    2
      unknown:                   0
  local changesets:             15
    common:                      7
    missing:                     8
  common heads: 01241442b3c2 b5714e113bc0
  
  % -- b -> a set (tip only)
  comparing with a
  query 1; heads
  searching for changes
  all remote heads known locally
  elapsed time:  * seconds (glob)
  heads summary:
    total common heads:          2
      also local heads:          1
      also remote heads:         2
      both:                      1
    local heads:                 3
      common:                    1
      missing:                   2
    remote heads:                2
      common:                    2
      unknown:                   0
  local changesets:             15
    common:                      7
    missing:                     8
  common heads: 01241442b3c2 b5714e113bc0


Many new:

  $ testdesc '-ra1 -ra2' '-rb' '
  > +2:f +3:a1 +3:b
  > <f +30 :a2'
  
  % -- a -> b tree
  comparing with b
  searching for changes
  unpruned common: bebd167eb94d
  elapsed time:  * seconds (glob)
  heads summary:
    total common heads:          1
      also local heads:          1
      also remote heads:         0
      both:                      0
    local heads:                 2
      common:                    1
      missing:                   1
    remote heads:                1
      common:                    0
      unknown:                   1
  local changesets:             35
    common:                      5
    missing:                    30
  common heads: bebd167eb94d
  
  % -- a -> b set
  comparing with b
  query 1; heads
  searching for changes
  taking initial sample
  searching: 2 queries
  query 2; still undecided: 29, sample size is: 29
  2 total queries in *.????s (glob)
  elapsed time:  * seconds (glob)
  heads summary:
    total common heads:          1
      also local heads:          1
      also remote heads:         0
      both:                      0
    local heads:                 2
      common:                    1
      missing:                   1
    remote heads:                1
      common:                    0
      unknown:                   1
  local changesets:             35
    common:                      5
    missing:                    30
  common heads: bebd167eb94d
  
  % -- a -> b set (tip only)
  comparing with b
  query 1; heads
  searching for changes
  taking quick initial sample
  searching: 2 queries
  query 2; still undecided: 31, sample size is: 31
  2 total queries in *.????s (glob)
  elapsed time:  * seconds (glob)
  heads summary:
    total common heads:          1
      also local heads:          0
      also remote heads:         0
      both:                      0
    local heads:                 2
      common:                    0
      missing:                   2
    remote heads:                1
      common:                    0
      unknown:                   1
  local changesets:             35
    common:                      2
    missing:                    33
  common heads: 66f7d451a68b
  
  % -- b -> a tree
  comparing with a
  searching for changes
  unpruned common: 66f7d451a68b bebd167eb94d
  elapsed time:  * seconds (glob)
  heads summary:
    total common heads:          1
      also local heads:          0
      also remote heads:         1
      both:                      0
    local heads:                 1
      common:                    0
      missing:                   1
    remote heads:                2
      common:                    1
      unknown:                   1
  local changesets:              8
    common:                      5
    missing:                     3
  common heads: bebd167eb94d
  
  % -- b -> a set
  comparing with a
  query 1; heads
  searching for changes
  taking initial sample
  searching: 2 queries
  query 2; still undecided: 2, sample size is: 2
  2 total queries in *.????s (glob)
  elapsed time:  * seconds (glob)
  heads summary:
    total common heads:          1
      also local heads:          0
      also remote heads:         1
      both:                      0
    local heads:                 1
      common:                    0
      missing:                   1
    remote heads:                2
      common:                    1
      unknown:                   1
  local changesets:              8
    common:                      5
    missing:                     3
  common heads: bebd167eb94d
  
  % -- b -> a set (tip only)
  comparing with a
  query 1; heads
  searching for changes
  taking initial sample
  searching: 2 queries
  query 2; still undecided: 2, sample size is: 2
  2 total queries in *.????s (glob)
  elapsed time:  * seconds (glob)
  heads summary:
    total common heads:          1
      also local heads:          0
      also remote heads:         1
      both:                      0
    local heads:                 1
      common:                    0
      missing:                   1
    remote heads:                2
      common:                    1
      unknown:                   1
  local changesets:              8
    common:                      5
    missing:                     3
  common heads: bebd167eb94d

Both sides many new with stub:

  $ testdesc '-ra1 -ra2' '-rb' '
  > +2:f +2:a1 +30 :b
  > <f +30 :a2'
  
  % -- a -> b tree
  comparing with b
  searching for changes
  unpruned common: 2dc09a01254d
  elapsed time:  * seconds (glob)
  heads summary:
    total common heads:          1
      also local heads:          1
      also remote heads:         0
      both:                      0
    local heads:                 2
      common:                    1
      missing:                   1
    remote heads:                1
      common:                    0
      unknown:                   1
  local changesets:             34
    common:                      4
    missing:                    30
  common heads: 2dc09a01254d
  
  % -- a -> b set
  comparing with b
  query 1; heads
  searching for changes
  taking initial sample
  searching: 2 queries
  query 2; still undecided: 29, sample size is: 29
  2 total queries in *.????s (glob)
  elapsed time:  * seconds (glob)
  heads summary:
    total common heads:          1
      also local heads:          1
      also remote heads:         0
      both:                      0
    local heads:                 2
      common:                    1
      missing:                   1
    remote heads:                1
      common:                    0
      unknown:                   1
  local changesets:             34
    common:                      4
    missing:                    30
  common heads: 2dc09a01254d
  
  % -- a -> b set (tip only)
  comparing with b
  query 1; heads
  searching for changes
  taking quick initial sample
  searching: 2 queries
  query 2; still undecided: 31, sample size is: 31
  2 total queries in *.????s (glob)
  elapsed time:  * seconds (glob)
  heads summary:
    total common heads:          1
      also local heads:          0
      also remote heads:         0
      both:                      0
    local heads:                 2
      common:                    0
      missing:                   2
    remote heads:                1
      common:                    0
      unknown:                   1
  local changesets:             34
    common:                      2
    missing:                    32
  common heads: 66f7d451a68b
  
  % -- b -> a tree
  comparing with a
  searching for changes
  unpruned common: 2dc09a01254d 66f7d451a68b
  elapsed time:  * seconds (glob)
  heads summary:
    total common heads:          1
      also local heads:          0
      also remote heads:         1
      both:                      0
    local heads:                 1
      common:                    0
      missing:                   1
    remote heads:                2
      common:                    1
      unknown:                   1
  local changesets:             34
    common:                      4
    missing:                    30
  common heads: 2dc09a01254d
  
  % -- b -> a set
  comparing with a
  query 1; heads
  searching for changes
  taking initial sample
  searching: 2 queries
  query 2; still undecided: 29, sample size is: 29
  2 total queries in *.????s (glob)
  elapsed time:  * seconds (glob)
  heads summary:
    total common heads:          1
      also local heads:          0
      also remote heads:         1
      both:                      0
    local heads:                 1
      common:                    0
      missing:                   1
    remote heads:                2
      common:                    1
      unknown:                   1
  local changesets:             34
    common:                      4
    missing:                    30
  common heads: 2dc09a01254d
  
  % -- b -> a set (tip only)
  comparing with a
  query 1; heads
  searching for changes
  taking initial sample
  searching: 2 queries
  query 2; still undecided: 29, sample size is: 29
  2 total queries in *.????s (glob)
  elapsed time:  * seconds (glob)
  heads summary:
    total common heads:          1
      also local heads:          0
      also remote heads:         1
      both:                      0
    local heads:                 1
      common:                    0
      missing:                   1
    remote heads:                2
      common:                    1
      unknown:                   1
  local changesets:             34
    common:                      4
    missing:                    30
  common heads: 2dc09a01254d


Both many new:

  $ testdesc '-ra' '-rb' '
  > +2:f +30 :b
  > <f +30 :a'
  
  % -- a -> b tree
  comparing with b
  searching for changes
  unpruned common: 66f7d451a68b
  elapsed time:  * seconds (glob)
  heads summary:
    total common heads:          1
      also local heads:          0
      also remote heads:         0
      both:                      0
    local heads:                 1
      common:                    0
      missing:                   1
    remote heads:                1
      common:                    0
      unknown:                   1
  local changesets:             32
    common:                      2
    missing:                    30
  common heads: 66f7d451a68b
  
  % -- a -> b set
  comparing with b
  query 1; heads
  searching for changes
  taking quick initial sample
  searching: 2 queries
  query 2; still undecided: 31, sample size is: 31
  2 total queries in *.????s (glob)
  elapsed time:  * seconds (glob)
  heads summary:
    total common heads:          1
      also local heads:          0
      also remote heads:         0
      both:                      0
    local heads:                 1
      common:                    0
      missing:                   1
    remote heads:                1
      common:                    0
      unknown:                   1
  local changesets:             32
    common:                      2
    missing:                    30
  common heads: 66f7d451a68b
  
  % -- a -> b set (tip only)
  comparing with b
  query 1; heads
  searching for changes
  taking quick initial sample
  searching: 2 queries
  query 2; still undecided: 31, sample size is: 31
  2 total queries in *.????s (glob)
  elapsed time:  * seconds (glob)
  heads summary:
    total common heads:          1
      also local heads:          0
      also remote heads:         0
      both:                      0
    local heads:                 1
      common:                    0
      missing:                   1
    remote heads:                1
      common:                    0
      unknown:                   1
  local changesets:             32
    common:                      2
    missing:                    30
  common heads: 66f7d451a68b
  
  % -- b -> a tree
  comparing with a
  searching for changes
  unpruned common: 66f7d451a68b
  elapsed time:  * seconds (glob)
  heads summary:
    total common heads:          1
      also local heads:          0
      also remote heads:         0
      both:                      0
    local heads:                 1
      common:                    0
      missing:                   1
    remote heads:                1
      common:                    0
      unknown:                   1
  local changesets:             32
    common:                      2
    missing:                    30
  common heads: 66f7d451a68b
  
  % -- b -> a set
  comparing with a
  query 1; heads
  searching for changes
  taking quick initial sample
  searching: 2 queries
  query 2; still undecided: 31, sample size is: 31
  2 total queries in *.????s (glob)
  elapsed time:  * seconds (glob)
  heads summary:
    total common heads:          1
      also local heads:          0
      also remote heads:         0
      both:                      0
    local heads:                 1
      common:                    0
      missing:                   1
    remote heads:                1
      common:                    0
      unknown:                   1
  local changesets:             32
    common:                      2
    missing:                    30
  common heads: 66f7d451a68b
  
  % -- b -> a set (tip only)
  comparing with a
  query 1; heads
  searching for changes
  taking quick initial sample
  searching: 2 queries
  query 2; still undecided: 31, sample size is: 31
  2 total queries in *.????s (glob)
  elapsed time:  * seconds (glob)
  heads summary:
    total common heads:          1
      also local heads:          0
      also remote heads:         0
      both:                      0
    local heads:                 1
      common:                    0
      missing:                   1
    remote heads:                1
      common:                    0
      unknown:                   1
  local changesets:             32
    common:                      2
    missing:                    30
  common heads: 66f7d451a68b


Both many new skewed:

  $ testdesc '-ra' '-rb' '
  > +2:f +30 :b
  > <f +50 :a'
  
  % -- a -> b tree
  comparing with b
  searching for changes
  unpruned common: 66f7d451a68b
  elapsed time:  * seconds (glob)
  heads summary:
    total common heads:          1
      also local heads:          0
      also remote heads:         0
      both:                      0
    local heads:                 1
      common:                    0
      missing:                   1
    remote heads:                1
      common:                    0
      unknown:                   1
  local changesets:             52
    common:                      2
    missing:                    50
  common heads: 66f7d451a68b
  
  % -- a -> b set
  comparing with b
  query 1; heads
  searching for changes
  taking quick initial sample
  searching: 2 queries
  query 2; still undecided: 51, sample size is: 51
  2 total queries in *.????s (glob)
  elapsed time:  * seconds (glob)
  heads summary:
    total common heads:          1
      also local heads:          0
      also remote heads:         0
      both:                      0
    local heads:                 1
      common:                    0
      missing:                   1
    remote heads:                1
      common:                    0
      unknown:                   1
  local changesets:             52
    common:                      2
    missing:                    50
  common heads: 66f7d451a68b
  
  % -- a -> b set (tip only)
  comparing with b
  query 1; heads
  searching for changes
  taking quick initial sample
  searching: 2 queries
  query 2; still undecided: 51, sample size is: 51
  2 total queries in *.????s (glob)
  elapsed time:  * seconds (glob)
  heads summary:
    total common heads:          1
      also local heads:          0
      also remote heads:         0
      both:                      0
    local heads:                 1
      common:                    0
      missing:                   1
    remote heads:                1
      common:                    0
      unknown:                   1
  local changesets:             52
    common:                      2
    missing:                    50
  common heads: 66f7d451a68b
  
  % -- b -> a tree
  comparing with a
  searching for changes
  unpruned common: 66f7d451a68b
  elapsed time:  * seconds (glob)
  heads summary:
    total common heads:          1
      also local heads:          0
      also remote heads:         0
      both:                      0
    local heads:                 1
      common:                    0
      missing:                   1
    remote heads:                1
      common:                    0
      unknown:                   1
  local changesets:             32
    common:                      2
    missing:                    30
  common heads: 66f7d451a68b
  
  % -- b -> a set
  comparing with a
  query 1; heads
  searching for changes
  taking quick initial sample
  searching: 2 queries
  query 2; still undecided: 31, sample size is: 31
  2 total queries in *.????s (glob)
  elapsed time:  * seconds (glob)
  heads summary:
    total common heads:          1
      also local heads:          0
      also remote heads:         0
      both:                      0
    local heads:                 1
      common:                    0
      missing:                   1
    remote heads:                1
      common:                    0
      unknown:                   1
  local changesets:             32
    common:                      2
    missing:                    30
  common heads: 66f7d451a68b
  
  % -- b -> a set (tip only)
  comparing with a
  query 1; heads
  searching for changes
  taking quick initial sample
  searching: 2 queries
  query 2; still undecided: 31, sample size is: 31
  2 total queries in *.????s (glob)
  elapsed time:  * seconds (glob)
  heads summary:
    total common heads:          1
      also local heads:          0
      also remote heads:         0
      both:                      0
    local heads:                 1
      common:                    0
      missing:                   1
    remote heads:                1
      common:                    0
      unknown:                   1
  local changesets:             32
    common:                      2
    missing:                    30
  common heads: 66f7d451a68b


Both many new on top of long history:

  $ testdesc '-ra' '-rb' '
  > +1000:f +30 :b
  > <f +50 :a'
  
  % -- a -> b tree
  comparing with b
  searching for changes
  unpruned common: 7ead0cba2838
  elapsed time:  * seconds (glob)
  heads summary:
    total common heads:          1
      also local heads:          0
      also remote heads:         0
      both:                      0
    local heads:                 1
      common:                    0
      missing:                   1
    remote heads:                1
      common:                    0
      unknown:                   1
  local changesets:           1050
    common:                   1000
    missing:                    50
  common heads: 7ead0cba2838
  
  % -- a -> b set
  comparing with b
  query 1; heads
  searching for changes
  taking quick initial sample
  searching: 2 queries
  query 2; still undecided: 1049, sample size is: 11
  sampling from both directions
  searching: 3 queries
  query 3; still undecided: 31, sample size is: 31
  3 total queries in *.????s (glob)
  elapsed time:  * seconds (glob)
  heads summary:
    total common heads:          1
      also local heads:          0
      also remote heads:         0
      both:                      0
    local heads:                 1
      common:                    0
      missing:                   1
    remote heads:                1
      common:                    0
      unknown:                   1
  local changesets:           1050
    common:                   1000
    missing:                    50
  common heads: 7ead0cba2838
  
  % -- a -> b set (tip only)
  comparing with b
  query 1; heads
  searching for changes
  taking quick initial sample
  searching: 2 queries
  query 2; still undecided: 1049, sample size is: 11
  sampling from both directions
  searching: 3 queries
  query 3; still undecided: 31, sample size is: 31
  3 total queries in *.????s (glob)
  elapsed time:  * seconds (glob)
  heads summary:
    total common heads:          1
      also local heads:          0
      also remote heads:         0
      both:                      0
    local heads:                 1
      common:                    0
      missing:                   1
    remote heads:                1
      common:                    0
      unknown:                   1
  local changesets:           1050
    common:                   1000
    missing:                    50
  common heads: 7ead0cba2838
  
  % -- b -> a tree
  comparing with a
  searching for changes
  unpruned common: 7ead0cba2838
  elapsed time:  * seconds (glob)
  heads summary:
    total common heads:          1
      also local heads:          0
      also remote heads:         0
      both:                      0
    local heads:                 1
      common:                    0
      missing:                   1
    remote heads:                1
      common:                    0
      unknown:                   1
  local changesets:           1030
    common:                   1000
    missing:                    30
  common heads: 7ead0cba2838
  
  % -- b -> a set
  comparing with a
  query 1; heads
  searching for changes
  taking quick initial sample
  searching: 2 queries
  query 2; still undecided: 1029, sample size is: 11
  sampling from both directions
  searching: 3 queries
  query 3; still undecided: 15, sample size is: 15
  3 total queries in *.????s (glob)
  elapsed time:  * seconds (glob)
  heads summary:
    total common heads:          1
      also local heads:          0
      also remote heads:         0
      both:                      0
    local heads:                 1
      common:                    0
      missing:                   1
    remote heads:                1
      common:                    0
      unknown:                   1
  local changesets:           1030
    common:                   1000
    missing:                    30
  common heads: 7ead0cba2838
  
  % -- b -> a set (tip only)
  comparing with a
  query 1; heads
  searching for changes
  taking quick initial sample
  searching: 2 queries
  query 2; still undecided: 1029, sample size is: 11
  sampling from both directions
  searching: 3 queries
  query 3; still undecided: 15, sample size is: 15
  3 total queries in *.????s (glob)
  elapsed time:  * seconds (glob)
  heads summary:
    total common heads:          1
      also local heads:          0
      also remote heads:         0
      both:                      0
    local heads:                 1
      common:                    0
      missing:                   1
    remote heads:                1
      common:                    0
      unknown:                   1
  local changesets:           1030
    common:                   1000
    missing:                    30
  common heads: 7ead0cba2838


One with >200 heads. We now switch to send them all in the initial roundtrip, but still do sampling for the later request.

  $ hg init manyheads
  $ cd manyheads
  $ echo "+300:r @a" >dagdesc
  $ echo "*r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3 *r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3" >>dagdesc # 20 heads
  $ echo "*r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3 *r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3" >>dagdesc # 20 heads
  $ echo "*r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3 *r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3" >>dagdesc # 20 heads
  $ echo "*r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3 *r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3" >>dagdesc # 20 heads
  $ echo "*r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3 *r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3" >>dagdesc # 20 heads
  $ echo "*r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3 *r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3" >>dagdesc # 20 heads
  $ echo "*r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3 *r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3" >>dagdesc # 20 heads
  $ echo "*r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3 *r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3" >>dagdesc # 20 heads
  $ echo "*r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3 *r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3" >>dagdesc # 20 heads
  $ echo "*r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3 *r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3" >>dagdesc # 20 heads
  $ echo "*r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3 *r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3" >>dagdesc # 20 heads
  $ echo "*r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3 *r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3" >>dagdesc # 20 heads
  $ echo "*r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3 *r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3*r+3" >>dagdesc # 20 heads
  $ echo "@b *r+3" >>dagdesc # one more head
  $ hg debugbuilddag <dagdesc
  reading DAG from stdin

  $ hg heads -t --template . | wc -c
  \s*261 (re)

  $ hg clone -b a . a
  adding changesets
  adding manifests
  adding file changes
  added 1340 changesets with 0 changes to 0 files (+259 heads)
  new changesets 1ea73414a91b:1c51e2c80832
  updating to branch a
  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg clone -b b . b
  adding changesets
  adding manifests
  adding file changes
  added 304 changesets with 0 changes to 0 files
  new changesets 1ea73414a91b:513314ca8b3a
  updating to branch b
  0 files updated, 0 files merged, 0 files removed, 0 files unresolved

  $ hg -R a debugdiscovery b --debug --verbose --config progress.debug=true
  comparing with b
  query 1; heads
  searching for changes
  taking quick initial sample
  searching: 2 queries
  query 2; still undecided: 1080, sample size is: 100
  sampling from both directions
  searching: 3 queries
  query 3; still undecided: 980, sample size is: 200
  sampling from both directions
  searching: 4 queries
  query 4; still undecided: 435, sample size is: 210
  sampling from both directions
  searching: 5 queries
  query 5; still undecided: 185, sample size is: 185
  5 total queries in *.????s (glob)
  elapsed time:  * seconds (glob)
  heads summary:
    total common heads:          1
      also local heads:          0
      also remote heads:         0
      both:                      0
    local heads:               260
      common:                    0
      missing:                 260
    remote heads:                1
      common:                    0
      unknown:                   1
  local changesets:           1340
    common:                    300
    missing:                  1040
  common heads: 3ee37d65064a
  $ hg -R a debugdiscovery b --debug --verbose --config progress.debug=true --rev tip
  comparing with b
  query 1; heads
  searching for changes
  taking quick initial sample
  searching: 2 queries
  query 2; still undecided: 303, sample size is: 9
  sampling from both directions
  searching: 3 queries
  query 3; still undecided: 3, sample size is: 3
  3 total queries in *.????s (glob)
  elapsed time:  * seconds (glob)
  heads summary:
    total common heads:          1
      also local heads:          0
      also remote heads:         0
      both:                      0
    local heads:               260
      common:                    0
      missing:                 260
    remote heads:                1
      common:                    0
      unknown:                   1
  local changesets:           1340
    common:                    300
    missing:                  1040
  common heads: 3ee37d65064a

Test actual protocol when pulling one new head in addition to common heads

  $ hg clone -U b c
  $ hg -R c id -ir tip
  513314ca8b3a
  $ hg -R c up -qr default
  $ touch c/f
  $ hg -R c ci -Aqm "extra head"
  $ hg -R c id -i
  e64a39e7da8b

  $ hg serve -R c -p $HGPORT -d --pid-file=hg.pid -A access.log -E errors.log
  $ cat hg.pid >> $DAEMON_PIDS

  $ hg -R b incoming http://localhost:$HGPORT/ -T '{node|short}\n'
  comparing with http://localhost:$HGPORT/
  searching for changes
  e64a39e7da8b

  $ killdaemons.py
  $ cut -d' ' -f6- access.log | grep -v cmd=known # cmd=known uses random sampling
  "GET /?cmd=capabilities HTTP/1.1" 200 -
  "GET /?cmd=batch HTTP/1.1" 200 - x-hgarg-1:cmds=heads+%3Bknown+nodes%3D513314ca8b3ae4dac8eec56966265b00fcf866db x-hgproto-1:0.1 0.2 comp=$USUAL_COMPRESSIONS$ partial-pull
  "GET /?cmd=getbundle HTTP/1.1" 200 - x-hgarg-1:$USUAL_BUNDLE_CAPS$&cg=1&common=513314ca8b3ae4dac8eec56966265b00fcf866db&heads=e64a39e7da8b0d54bc63e81169aff001c13b3477 x-hgproto-1:0.1 0.2 comp=$USUAL_COMPRESSIONS$ partial-pull
  "GET /?cmd=listkeys HTTP/1.1" 200 - x-hgarg-1:namespace=phases x-hgproto-1:0.1 0.2 comp=$USUAL_COMPRESSIONS$ partial-pull
  $ cat errors.log

  $ cd ..


Issue 4438 - test coverage for 3ef893520a85 issues.

  $ mkdir issue4438
  $ cd issue4438
#if false
generate new bundles:
  $ hg init r1
  $ for i in `"$PYTHON" $TESTDIR/seq.py 101`; do hg -R r1 up -qr null && hg -R r1 branch -q b$i && hg -R r1 ci -qmb$i; done
  $ hg clone -q r1 r2
  $ for i in `"$PYTHON" $TESTDIR/seq.py 10`; do hg -R r1 up -qr null && hg -R r1 branch -q c$i && hg -R r1 ci -qmc$i; done
  $ hg -R r2 branch -q r2change && hg -R r2 ci -qmr2change
  $ hg -R r1 bundle -qa $TESTDIR/bundles/issue4438-r1.hg
  $ hg -R r2 bundle -qa $TESTDIR/bundles/issue4438-r2.hg
#else
use existing bundles:
  $ hg init r1
  $ hg -R r1 -q unbundle $TESTDIR/bundles/issue4438-r1.hg
  $ hg -R r1 -q up
  $ hg init r2
  $ hg -R r2 -q unbundle $TESTDIR/bundles/issue4438-r2.hg
  $ hg -R r2 -q up
#endif

Set iteration order could cause wrong and unstable results - fixed in 73cfaa348650:

  $ hg -R r1 outgoing r2 -T'{rev} '
  comparing with r2
  searching for changes
  101 102 103 104 105 106 107 108 109 110  (no-eol)

The case where all the 'initialsamplesize' samples already were common would
give 'all remote heads known locally' without checking the remaining heads -
fixed in 86c35b7ae300:

  $ cat >> $TESTTMP/unrandomsample.py << EOF
  > import random
  > def sample(population, k):
  >     return sorted(population)[:k]
  > random.sample = sample
  > EOF

  $ cat >> r1/.hg/hgrc << EOF
  > [extensions]
  > unrandomsample = $TESTTMP/unrandomsample.py
  > EOF

  $ hg -R r1 outgoing r2 -T'{rev} ' --config extensions.blackbox= \
  > --config blackbox.track='command commandfinish discovery'
  comparing with r2
  searching for changes
  101 102 103 104 105 106 107 108 109 110  (no-eol)
  $ hg -R r1 --config extensions.blackbox= blackbox --config blackbox.track=
  * @5d0b986a083e0d91f116de4691e2aaa54d5bbec0 (*)> serve --cmdserver chgunix * (glob) (chg !)
  * @5d0b986a083e0d91f116de4691e2aaa54d5bbec0 (*)> -R r1 outgoing r2 *-T{rev} * --config *extensions.blackbox=* (glob)
  * @5d0b986a083e0d91f116de4691e2aaa54d5bbec0 (*)> found 101 common and 1 unknown server heads, 1 roundtrips in *.????s (glob)
  * @5d0b986a083e0d91f116de4691e2aaa54d5bbec0 (*)> -R r1 outgoing r2 *-T{rev} * --config *extensions.blackbox=* exited 0 after *.?? seconds (glob)
  $ cd ..