tests/test-persistent-nodemap.t

nodemap: introduce an option to use mmap to read the nodemap mapping

The performance and memory benefit is much greater if we don't have to copy all
the data in memory for each information. So we introduce an option (on by
default) to read the data using mmap.

This changeset is the last one definition the API for index support nodemap
data. (they have to be able to use the mmaping).

Below are some benchmark comparing the best we currently have in 5.3 with the
final step of this series (using the persistent nodemap implementation in
Rust). The benchmark run `hg perfindex` with various revset and the following
variants:

Before:

 * do not use the persistent nodemap
 * use the CPython implementation of the index for nodemap
 * use mmapping of the changelog index

After:

 * use the MixedIndex Rust code, with the NodeTree object for nodemap access
   (still in review)
 * use the persistent nodemap data from disk
 * access the persistent nodemap data through mmap
 * use mmapping of the changelog index

The persistent nodemap greatly speed up  most operation on very large
repositories. Some of the previously very fast lookup end up a bit slower because
the persistent nodemap has to be setup. However the absolute slowdown is very
small and won't matters in the big picture.

Here are some numbers (in seconds) for the reference copy of mozilla-try:

Revset            Before   After     abs-change speedup

-10000:           0.004622 0.005532   0.000910  ×   0.83
-10:              0.000050 0.000132   0.000082  ×   0.37
tip               0.000052 0.000085   0.000033  ×   0.61
0 + (-10000:)     0.028222 0.005337  -0.022885  ×   5.29
0                 0.023521 0.000084  -0.023437  × 280.01
(-10000:) + 0     0.235539 0.005308  -0.230231  ×  44.37
(-10:) + :9       0.232883 0.000180  -0.232703  ×1293.79
(-10000:) + (:99) 0.238735 0.005358  -0.233377  ×  44.55
:99 + (-10000:)   0.317942 0.005593  -0.312349  ×  56.84
:9 + (-10:)       0.313372 0.000179  -0.313193  ×1750.68
:9                0.316450 0.000143  -0.316307  ×2212.93


On smaller repositories, the cost of nodemap related operation is not as big, so
the win is much more modest. Yet it helps shaving a handful of millisecond here
and there.

Here are some numbers (in seconds) for the reference copy of mercurial:

Revset            Before   After     abs-change speedup
-10:              0.000065 0.000097   0.000032  × 0.67
tip               0.000063 0.000078   0.000015  × 0.80
0                 0.000561 0.000079  -0.000482  × 7.10
-10000:           0.004609 0.003648  -0.000961  × 1.26
0 + (-10000:)     0.005023 0.003715  -0.001307  × 1.35
(-10:) + :9       0.002187 0.000108  -0.002079  ×20.25
(-10000:) + 0     0.006252 0.003716  -0.002536  × 1.68
(-10000:) + (:99) 0.006367 0.003707  -0.002660  × 1.71
:9 + (-10:)       0.003846 0.000110  -0.003736  ×34.96
:9                0.003854 0.000099  -0.003755  ×38.92
:99 + (-10000:)   0.007644 0.003778  -0.003866  × 2.02

Differential Revision: https://phab.mercurial-scm.org/D7894

===================================
Test the persistent on-disk nodemap
===================================


  $ hg init test-repo
  $ cd test-repo
  $ cat << EOF >> .hg/hgrc
  > [experimental]
  > exp-persistent-nodemap=yes
  > [devel]
  > persistent-nodemap=yes
  > EOF
  $ hg debugbuilddag .+5000
  $ hg debugnodemap --metadata
  uid: ???????????????? (glob)
  tip-rev: 5000
  data-length: 122880
  data-unused: 0
  $ f --size .hg/store/00changelog.n
  .hg/store/00changelog.n: size=42
  $ f --sha256 .hg/store/00changelog-*.nd
  .hg/store/00changelog-????????????????.nd: sha256=b961925120e1c9bc345c199b2cc442abc477029fdece37ef9d99cbe59c0558b7 (glob)
  $ hg debugnodemap --dump-new | f --sha256 --size
  size=122880, sha256=b961925120e1c9bc345c199b2cc442abc477029fdece37ef9d99cbe59c0558b7
  $ hg debugnodemap --dump-disk | f --sha256 --bytes=256 --hexdump --size
  size=122880, sha256=b961925120e1c9bc345c199b2cc442abc477029fdece37ef9d99cbe59c0558b7
  0000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff |................|
  0010: ff ff ff ff ff ff ff ff ff ff fa c2 ff ff ff ff |................|
  0020: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff |................|
  0030: ff ff ff ff ff ff ed b3 ff ff ff ff ff ff ff ff |................|
  0040: ff ff ff ff ff ff ee 34 00 00 00 00 ff ff ff ff |.......4........|
  0050: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff |................|
  0060: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff |................|
  0070: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff |................|
  0080: ff ff ff ff ff ff f8 50 ff ff ff ff ff ff ff ff |.......P........|
  0090: ff ff ff ff ff ff ff ff ff ff ec c7 ff ff ff ff |................|
  00a0: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff |................|
  00b0: ff ff ff ff ff ff fa be ff ff f2 fc ff ff ff ff |................|
  00c0: ff ff ff ff ff ff ef ea ff ff ff ff ff ff f9 17 |................|
  00d0: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff |................|
  00e0: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff |................|
  00f0: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff |................|
  $ hg debugnodemap --check
  revision in index:   5001
  revision in nodemap: 5001

add a new commit

  $ hg up
  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ echo foo > foo
  $ hg add foo
  $ hg ci -m 'foo'

#if pure
  $ hg debugnodemap --metadata
  uid: ???????????????? (glob)
  tip-rev: 5001
  data-length: 123072
  data-unused: 192
#else
  $ hg debugnodemap --metadata
  uid: ???????????????? (glob)
  tip-rev: 5001
  data-length: 122880
  data-unused: 0
#endif
  $ f --size .hg/store/00changelog.n
  .hg/store/00changelog.n: size=42

(The pure code use the debug code that perform incremental update, the C code reencode from scratch)

#if pure
  $ f --sha256 .hg/store/00changelog-*.nd --size
  .hg/store/00changelog-????????????????.nd: size=123072, sha256=136472751566c8198ff09e306a7d2f9bd18bd32298d614752b73da4d6df23340 (glob)

#else
  $ f --sha256 .hg/store/00changelog-*.nd --size
  .hg/store/00changelog-????????????????.nd: size=122880, sha256=bfafebd751c4f6d116a76a37a1dee2a251747affe7efbcc4f4842ccc746d4db9 (glob)

#endif

  $ hg debugnodemap --check
  revision in index:   5002
  revision in nodemap: 5002

Test code path without mmap
---------------------------

  $ echo bar > bar
  $ hg add bar
  $ hg ci -m 'bar' --config experimental.exp-persistent-nodemap.mmap=no

  $ hg debugnodemap --check --config experimental.exp-persistent-nodemap.mmap=yes
  revision in index:   5003
  revision in nodemap: 5003
  $ hg debugnodemap --check --config experimental.exp-persistent-nodemap.mmap=no
  revision in index:   5003
  revision in nodemap: 5003


#if pure
  $ hg debugnodemap --metadata
  uid: ???????????????? (glob)
  tip-rev: 5002
  data-length: 123328
  data-unused: 384
  $ f --sha256 .hg/store/00changelog-*.nd --size
  .hg/store/00changelog-????????????????.nd: size=123328, sha256=10d26e9776b6596af0f89143a54eba8cc581e929c38242a02a7b0760698c6c70 (glob)

#else
  $ hg debugnodemap --metadata
  uid: ???????????????? (glob)
  tip-rev: 5002
  data-length: 122944
  data-unused: 0
  $ f --sha256 .hg/store/00changelog-*.nd --size
  .hg/store/00changelog-????????????????.nd: size=122944, sha256=755976b22b64ab680401b45395953504e64e7fa8c31ac570f58dee21e15f9bc0 (glob)
#endif