view tests/test-obsolete-tag-cache.t @ 26379:39d643252b9f

revlog: use existing file handle when reading during _addrevision

_addrevision() may need to read from revlogs as part of computing
deltas. Previously, we would flush existing file handles and open
a new, short-lived file handle to perform the reading.

If we have an existing file handle, it seems logical to reuse it
for reading instead of opening a new file handle. This patch
makes that the new behavior.

After this patch, revlog files are only reopened when adding
revisions if the revlog is switched from inline to non-inline.

On Linux when unbundling a bundle of the mozilla-central repo, this
patch has the following impact on system call counts:

Call     Before     After       Delta
write    827,639    673,390   -154,249
open     700,103    684,089    -16,014
read      74,489     74,489          0
fstat    493,924    461,896    -32,028
close    249,131    233,117    -16,014
stat     242,001    242,001          0
lstat     18,676     18,676          0
lseek     20,268     20,268          0
ioctl     14,652     13,173     -1,479
TOTAL  3,180,758  2,930,679   -250,079

It's worth noting that many of the open() calls fail due to missing
files. That's why there are many more open() calls than close().

Despite the significant system call reduction, this change does not
seem to have a significant performance impact on Linux.

On Windows 10 (not a VM, on a SSD), this patch appears to reduce
unbundle time for mozilla-central from ~960s to ~920s. This isn't
as significant as I was hoping. But a decrease it is nonetheless.
Still, Windows unbundle performance is still >2x slower than Linux.

Despite the lack of significant gains, fewer system calls is fewer
system calls. If nothing else, this will narrow the focus of potential
areas to optimize in the future.

  $ cat >> $HGRCPATH << EOF
  > [extensions]
  > blackbox=
  > rebase=
  > mock=$TESTDIR/mockblackbox.py
  > 
  > [experimental]
  > evolution = createmarkers
  > EOF

Create a repo with some tags

  $ hg init repo
  $ cd repo
  $ echo initial > foo
  $ hg -q commit -A -m initial
  $ hg tag -m 'test tag' test1
  $ echo first > first
  $ hg -q commit -A -m first
  $ hg tag -m 'test2 tag' test2
  $ hg -q up -r 0
  $ echo newhead > newhead
  $ hg commit -A -m newhead
  adding newhead
  created new head
  $ hg tag -m 'test head 2 tag' head2

  $ hg log -G -T '{rev}:{node|short} {tags} {desc}\n'
  @  5:2942a772f72a tip test head 2 tag
  |
  o  4:042eb6bfcc49 head2 newhead
  |
  | o  3:c3cb30f2d2cd  test2 tag
  | |
  | o  2:d75775ffbc6b test2 first
  | |
  | o  1:5f97d42da03f  test tag
  |/
  o  0:55482a6fb4b1 test1 initial
  

Trigger tags cache population by doing something that accesses tags info

  $ hg tags
  tip                                5:2942a772f72a
  head2                              4:042eb6bfcc49
  test2                              2:d75775ffbc6b
  test1                              0:55482a6fb4b1

  $ cat .hg/cache/tags2-visible
  5 2942a772f72a444bef4bef13874d515f50fa27b6
  042eb6bfcc4909bad84a1cbf6eb1ddf0ab587d41 head2
  55482a6fb4b1881fa8f746fd52cf6f096bb21c89 test1
  d75775ffbc6bca1794d300f5571272879bd280da test2

Hiding a non-tip changeset should change filtered hash and cause tags recompute

  $ hg debugobsolete -d '0 0' c3cb30f2d2cd0aae008cc91a07876e3c5131fd22 -u dummyuser

  $ hg tags
  tip                                5:2942a772f72a
  head2                              4:042eb6bfcc49
  test1                              0:55482a6fb4b1

  $ cat .hg/cache/tags2-visible
  5 2942a772f72a444bef4bef13874d515f50fa27b6 f34fbc9a9769ba9eff5aff3d008a6b49f85c08b1
  042eb6bfcc4909bad84a1cbf6eb1ddf0ab587d41 head2
  55482a6fb4b1881fa8f746fd52cf6f096bb21c89 test1

  $ hg blackbox -l 4
  1970/01/01 00:00:00 bob (*)> tags (glob)
  1970/01/01 00:00:00 bob (*)> 2/2 cache hits/lookups in * seconds (glob)
  1970/01/01 00:00:00 bob (*)> writing .hg/cache/tags2-visible with 2 tags (glob)
  1970/01/01 00:00:00 bob (*)> tags exited 0 after * seconds (glob)

Hiding another changeset should cause the filtered hash to change

  $ hg debugobsolete -d '0 0' d75775ffbc6bca1794d300f5571272879bd280da -u dummyuser
  $ hg debugobsolete -d '0 0' 5f97d42da03fd56f3b228b03dfe48af5c0adf75b -u dummyuser

  $ hg tags
  tip                                5:2942a772f72a
  head2                              4:042eb6bfcc49

  $ cat .hg/cache/tags2-visible
  5 2942a772f72a444bef4bef13874d515f50fa27b6 2fce1eec33263d08a4d04293960fc73a555230e4
  042eb6bfcc4909bad84a1cbf6eb1ddf0ab587d41 head2

  $ hg blackbox -l 4
  1970/01/01 00:00:00 bob (*)> tags (glob)
  1970/01/01 00:00:00 bob (*)> 1/1 cache hits/lookups in * seconds (glob)
  1970/01/01 00:00:00 bob (*)> writing .hg/cache/tags2-visible with 1 tags (glob)
  1970/01/01 00:00:00 bob (*)> tags exited 0 after * seconds (glob)

Resolving tags on an unfiltered repo writes a separate tags cache

  $ hg --hidden tags
  tip                                5:2942a772f72a
  head2                              4:042eb6bfcc49
  test2                              2:d75775ffbc6b
  test1                              0:55482a6fb4b1

  $ cat .hg/cache/tags2
  5 2942a772f72a444bef4bef13874d515f50fa27b6
  042eb6bfcc4909bad84a1cbf6eb1ddf0ab587d41 head2
  55482a6fb4b1881fa8f746fd52cf6f096bb21c89 test1
  d75775ffbc6bca1794d300f5571272879bd280da test2

  $ hg blackbox -l 4
  1970/01/01 00:00:00 bob (*)> --hidden tags (glob)
  1970/01/01 00:00:00 bob (*)> 2/2 cache hits/lookups in * seconds (glob)
  1970/01/01 00:00:00 bob (*)> writing .hg/cache/tags2 with 3 tags (glob)
  1970/01/01 00:00:00 bob (*)> --hidden tags exited 0 after * seconds (glob)