nodemap: gate the feature behind a new requirement
Now that the feature is working smoothly, a question was still open, should we
gate the feature behind a new requirement or just treat it as a cache to be
warmed by those who can and ignored by other.
The advantage of using the cache approach is a transparent upgrade/downgrade
story, making the feature easier to move to. However having out of date cache
can come with a significant performance hit for process who expect an up to
date cache but found none. In this case the file needs to be stored under
`.hg/cache`.
The "requirement" approach guarantee that the persistent nodemap is up to date.
However, it comes with a less flexible activation story since an explicite
upgrade is required. In this case the file can be stored in `.hg/store`.
This wiki page is relevant to this questions:
https://www.mercurial-scm.org/wiki/ComputedIndexPlan
So which one should we take? Another element came into plan, the persistent
nodemap use the `add` method of the transaction, it is used to keep track of a
file content before a transaction in case we need to rollback it back. It turns
out that the `transaction.add` API does not support file stored anywhere than
`.hg/store`. Making it support file stored elsewhere is possible, require a
change in on disk transaction format. Updating on disk file requires…
introducing a new requirements.
As a result, we pick the second option "gating the persistent nodemap behind a
new requirements".
Differential Revision: https://phab.mercurial-scm.org/D8417
# this file holds the definitions that are used in various bzr tests
TERM=dumb; export TERM
echo '[extensions]' >> $HGRCPATH
echo 'convert = ' >> $HGRCPATH
glog()
{
hg log -G --template '{rev}@{branch} "{desc|firstline}" files+: [{file_adds}], files-: [{file_dels}], files: [{file_mods}]\n' "$@"
}
manifest()
{
echo "% manifest of $2"
hg -R $1 manifest -v -r $2
}