view tests/test-cache-abuse.t @ 47120:7109a38830c9

dirstate-tree: Fold "tracked descendants" counter update in main walk

For the purpose of implementing `has_tracked_dir` (which means "has tracked
descendants) without an expensive sub-tree traversal, we maintaing a counter
of tracked descendants on each "directory" node of the tree-shaped dirstate.

Before this changeset, mutating or inserting a node at a given path would
involve:

* Walking the tree from root through ancestors to find the node or the spot
  where to insert it
* Looking at the previous node if any to decide what counter update is needed
* Performing any node mutation
* Walking the tree *again* to update counters in ancestor nodes

When profiling `hg status` on a large repo, this second walk takes times
while loading a the dirstate from disk.

It turns out we have enough information to decide before he first tree walk
what counter update is needed. This changeset merges the two walks, gaining
~10% of the total time for `hg update` (in the same hyperfine benchmark as
the previous changeset).

---

Profiling was done by compiling with this `.cargo/config`:

    [profile.release]
    debug = true

then running with:

    py-spy record -r 500 -n -o /tmp/hg.json --format speedscope -- \
    ./hg status -R $REPO --config experimental.dirstate-tree.in-memory=1

then visualizing the recorded JSON file in https://www.speedscope.app/

Differential Revision: https://phab.mercurial-scm.org/D10554

Enable obsolete markers

  $ cat >> $HGRCPATH << EOF
  > [experimental]
  > evolution.createmarkers=True
  > [phases]
  > publish=False
  > EOF

Build a repo with some cacheable bits:

  $ hg init a
  $ cd a

  $ echo a > a
  $ hg ci -qAm0
  $ hg tag t1
  $ hg book -i bk1

  $ hg branch -q b2
  $ hg ci -Am1
  $ hg tag t2

  $ echo dumb > dumb
  $ hg ci -qAmdumb
  $ hg debugobsolete b1174d11b69e63cb0c5726621a43c859f0858d7f
  1 new obsolescence markers
  obsoleted 1 changesets

  $ hg phase -pr t1
  $ hg phase -fsr t2

Make a helper function to check cache damage invariants:

- command output shouldn't change
- cache should be present after first use
- corruption/repair should be silent (no exceptions or warnings)
- cache should survive deletion, overwrite, and append
- unreadable / unwriteable caches should be ignored
- cache should be rebuilt after corruption

  $ damage() {
  >  CMD=$1
  >  CACHE=.hg/cache/$2
  >  CLEAN=$3
  >  hg $CMD > before
  >  test -f $CACHE || echo "not present"
  >  echo bad > $CACHE
  >  test -z "$CLEAN" || $CLEAN
  >  hg $CMD > after
  >  "$RUNTESTDIR/pdiff" before after || echo "*** overwrite corruption"
  >  echo corruption >> $CACHE
  >  test -z "$CLEAN" || $CLEAN
  >  hg $CMD > after
  >  "$RUNTESTDIR/pdiff" before after || echo "*** append corruption"
  >  rm $CACHE
  >  mkdir $CACHE
  >  test -z "$CLEAN" || $CLEAN
  >  hg $CMD > after
  >  "$RUNTESTDIR/pdiff" before after || echo "*** read-only corruption"
  >  test -d $CACHE || echo "*** directory clobbered"
  >  rmdir $CACHE
  >  test -z "$CLEAN" || $CLEAN
  >  hg $CMD > after
  >  "$RUNTESTDIR/pdiff" before after || echo "*** missing corruption"
  >  test -f $CACHE || echo "not rebuilt"
  > }

Beat up tags caches:

  $ damage "tags --hidden" tags2
  $ damage tags tags2-visible
  $ damage "tag -f t3" hgtagsfnodes1
  1 new orphan changesets
  1 new orphan changesets
  1 new orphan changesets
  1 new orphan changesets
  1 new orphan changesets

Beat up branch caches:

  $ damage branches branch2-base "rm .hg/cache/branch2-[vs]*"
  $ damage branches branch2-served "rm .hg/cache/branch2-[bv]*"
  $ damage branches branch2-visible
  $ damage "log -r branch(.)" rbc-names-v1
  $ damage "log -r branch(default)" rbc-names-v1
  $ damage "log -r branch(b2)" rbc-revs-v1

We currently can't detect an rbc cache with unknown names:

  $ damage "log -qr branch(b2)" rbc-names-v1
  --- before	* (glob)
  +++ after	* (glob)
  @@ -1,8 +?,0 @@ (glob)
  -2:5fb7d38b9dc4
  -3:60b597ffdafa
  -4:b1174d11b69e
  -5:6354685872c0
  -6:5ebc725f1bef
  -7:7b76eec2f273
  -8:ef3428d9d644
  -9:ba7a936bc03c
  *** append corruption