tests/test-rebase-backup.t

util: lower water mark when removing nodes after cost limit reached

See the inline comment for the reasoning here. This is a pretty
common strategy for garbage collectors, other cache-like primtives.

The performance impact is substantial:

$ hg perflrucachedict --size 4 --gets 1000000 --sets 1000000 --mixed 1000000 --costlimit 100
! inserts w/ cost limit
! wall 1.659181 comb 1.650000 user 1.650000 sys 0.000000 (best of 7)
! wall 1.722122 comb 1.720000 user 1.720000 sys 0.000000 (best of 6)
! mixed w/ cost limit
! wall 1.139955 comb 1.140000 user 1.140000 sys 0.000000 (best of 9)
! wall 1.182513 comb 1.180000 user 1.180000 sys 0.000000 (best of 9)

$ hg perflrucachedict --size 1000 --gets 1000000 --sets 1000000 --mixed 1000000 --costlimit 10000
! inserts
! wall 0.679546 comb 0.680000 user 0.680000 sys 0.000000 (best of 15)
! sets
! wall 0.825147 comb 0.830000 user 0.830000 sys 0.000000 (best of 13)
! inserts w/ cost limit
! wall 25.105273 comb 25.080000 user 25.080000 sys 0.000000 (best of 3)
! wall  1.724397 comb  1.720000 user  1.720000 sys 0.000000 (best of 6)
! mixed
! wall 0.807096 comb 0.810000 user 0.810000 sys 0.000000 (best of 13)
! mixed w/ cost limit
! wall 12.104470 comb 12.070000 user 12.070000 sys 0.000000 (best of 3)
! wall  1.190563 comb  1.190000 user  1.190000 sys 0.000000 (best of 9)

$ hg perflrucachedict --size 1000 --gets 1000000 --sets 1000000 --mixed 1000000 --costlimit 10000 --mixedgetfreq 90
! inserts
! wall 0.711177 comb 0.710000 user 0.710000 sys 0.000000 (best of 14)
! sets
! wall 0.846992 comb 0.850000 user 0.850000 sys 0.000000 (best of 12)
! inserts w/ cost limit
! wall 25.963028 comb 25.960000 user 25.960000 sys 0.000000 (best of 3)
! wall  2.184311 comb  2.180000 user  2.180000 sys 0.000000 (best of 5)
! mixed
! wall 0.728256 comb 0.730000 user 0.730000 sys 0.000000 (best of 14)
! mixed w/ cost limit
! wall 3.174256 comb 3.170000 user 3.170000 sys 0.000000 (best of 4)
! wall 0.773186 comb 0.770000 user 0.770000 sys 0.000000 (best of 13)

$ hg perflrucachedict --size 100000 --gets 1000000 --sets 1000000 --mixed 1000000 --mixedgetfreq 90 --costlimit 5000000
! gets
! wall 1.191368 comb 1.190000 user 1.190000 sys 0.000000 (best of 9)
! wall 1.195304 comb 1.190000 user 1.190000 sys 0.000000 (best of 9)
! inserts
! wall 0.950995 comb 0.950000 user 0.950000 sys 0.000000 (best of 11)
! inserts w/ cost limit
! wall 1.589732 comb 1.590000 user 1.590000 sys 0.000000 (best of 7)
! sets
! wall 1.094941 comb 1.100000 user 1.090000 sys 0.010000 (best of 9)
! mixed
! wall 0.936420 comb 0.940000 user 0.930000 sys 0.010000 (best of 10)
! mixed w/ cost limit
! wall 0.882780 comb 0.870000 user 0.870000 sys 0.000000 (best of 11)

This puts us ~2x slower than caches without cost accounting. And for
read-heavy workloads (the prime use cases for caches), performance is
nearly identical.

In the worst case (pure write workloads with cost accounting enabled),
we're looking at ~1.5us per insert on large caches. That seems "fast
enough."

Differential Revision: https://phab.mercurial-scm.org/D4505

  $ cat << EOF >> $HGRCPATH
  > [extensions]
  > rebase=
  > EOF

==========================================
Test history-editing-backup config option |
==========================================
Test with Pre-obsmarker rebase:
1) When config option is not set:
  $ hg init repo1
  $ cd repo1
  $ echo a>a
  $ hg ci -qAma
  $ echo b>b
  $ hg ci -qAmb
  $ echo c>c
  $ hg ci -qAmc
  $ hg up 0 -q
  $ echo d>d
  $ hg ci -qAmd
  $ echo e>e
  $ hg ci -qAme
  $ hg log -GT "{rev}: {firstline(desc)}\n"
  @  4: e
  |
  o  3: d
  |
  | o  2: c
  | |
  | o  1: b
  |/
  o  0: a
  
  $ hg rebase -s 1 -d .
  rebasing 1:d2ae7f538514 "b"
  rebasing 2:177f92b77385 "c"
  saved backup bundle to $TESTTMP/repo1/.hg/strip-backup/d2ae7f538514-c7ed7a78-rebase.hg
  $ hg log -GT "{rev}: {firstline(desc)}\n"
  o  4: c
  |
  o  3: b
  |
  @  2: e
  |
  o  1: d
  |
  o  0: a
  

2) When config option is set:
  $ cat << EOF >> $HGRCPATH
  > [ui]
  > history-editing-backup = False
  > EOF

  $ echo f>f
  $ hg ci -Aqmf
  $ echo g>g
  $ hg ci -Aqmg
  $ hg log -GT "{rev}: {firstline(desc)}\n"
  @  6: g
  |
  o  5: f
  |
  | o  4: c
  | |
  | o  3: b
  |/
  o  2: e
  |
  o  1: d
  |
  o  0: a
  
  $ hg rebase -s 3 -d .
  rebasing 3:05bff2a95b12 "b"
  rebasing 4:1762bde4404d "c"

  $ hg log -GT "{rev}: {firstline(desc)}\n"
  o  6: c
  |
  o  5: b
  |
  @  4: g
  |
  o  3: f
  |
  o  2: e
  |
  o  1: d
  |
  o  0: a
  
Test when rebased revisions are stripped during abort:
======================================================

  $ echo conflict > c
  $ hg ci -Am "conflict with c"
  adding c
  created new head
  $ hg log -GT "{rev}: {firstline(desc)}\n"
  @  7: conflict with c
  |
  | o  6: c
  | |
  | o  5: b
  |/
  o  4: g
  |
  o  3: f
  |
  o  2: e
  |
  o  1: d
  |
  o  0: a
  
When history-editing-backup = True:
  $ cat << EOF >> $HGRCPATH
  > [ui]
  > history-editing-backup = True
  > EOF
  $ hg rebase -s 5 -d .
  rebasing 5:1f8148a544ee "b"
  rebasing 6:f8bc7d28e573 "c"
  merging c
  warning: conflicts while merging c! (edit, then use 'hg resolve --mark')
  unresolved conflicts (see hg resolve, then hg rebase --continue)
  [1]
  $ hg rebase --abort
  saved backup bundle to $TESTTMP/repo1/.hg/strip-backup/818c1a43c916-2b644d96-backup.hg
  rebase aborted

When history-editing-backup = False:
  $ cat << EOF >> $HGRCPATH
  > [ui]
  > history-editing-backup = False
  > EOF
  $ hg rebase -s 5 -d .
  rebasing 5:1f8148a544ee "b"
  rebasing 6:f8bc7d28e573 "c"
  merging c
  warning: conflicts while merging c! (edit, then use 'hg resolve --mark')
  unresolved conflicts (see hg resolve, then hg rebase --continue)
  [1]
  $ hg rebase --abort
  rebase aborted
  $ cd ..