view tests/test-update-reverse.t @ 23810:b681d3a2bf04

setdiscovery: randomly pick between heads and sample when taking full sample

Before this changeset, the discovery protocol was too heads-centric. Heads of the
undiscovered set were always sent for discovery and any room remaining in the
sample were filled with exponential samples (and random ones if any room
remained).

This behaved extremely poorly when the number of heads exceeded the sample size,
because we keep just asking about the existence of heads, then their direct parent
and so on. As a result, the 'O(log(len(repo)))' discovery turns into a
'O(len(repo))' one. As a solution we take a random sample of the heads plus
exponential samples. This way we ensure some exponential sampling is achieved,
bringing back some logarithmic convergence of the discovery again.

This patch only applies this principle in one place. More places will be updated
in future patches.

One test is impacted because the random sample happen to be different. By
chance, it helps a bit in this case.

  $ hg init

  $ touch a
  $ hg add a
  $ hg commit -m "Added a"

  $ touch main
  $ hg add main
  $ hg commit -m "Added main"
  $ hg checkout 0
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved

'main' should be gone:

  $ ls
  a

  $ touch side1
  $ hg add side1
  $ hg commit -m "Added side1"
  created new head
  $ touch side2
  $ hg add side2
  $ hg commit -m "Added side2"

  $ hg log
  changeset:   3:91ebc10ed028
  tag:         tip
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     Added side2
  
  changeset:   2:b932d7dbb1e1
  parent:      0:c2eda428b523
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     Added side1
  
  changeset:   1:71a760306caf
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     Added main
  
  changeset:   0:c2eda428b523
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     Added a
  

  $ hg heads
  changeset:   3:91ebc10ed028
  tag:         tip
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     Added side2
  
  changeset:   1:71a760306caf
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     Added main
  
  $ ls
  a
  side1
  side2

  $ hg update --debug -C 1
  resolving manifests
   branchmerge: False, force: True, partial: False
   ancestor: 91ebc10ed028+, local: 91ebc10ed028+, remote: 71a760306caf
   side1: other deleted -> r
  removing side1
   side2: other deleted -> r
  removing side2
  updating: side2 2/3 files (66.67%)
   main: remote created -> g
  getting main
  updating: main 3/3 files (100.00%)
  1 files updated, 0 files merged, 2 files removed, 0 files unresolved

  $ ls
  a
  main