branchcache: skip entries that are topological heads in the on disk file
In the majority of cases, topological heads are also branch heads. We have
efficient way to get the topological heads and efficient way to retrieve
their branch information. So there is little value in putting them in the branch
cache file explicitly. On the contrary, writing them explicitly tend to create
very large cache file that are inefficient to read and update.
So the branch cache v3 format is no longer including them. This changeset focus
on the format aspect and have no focus on the performance aspect. We will cover
that later.
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