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 However having out of date cache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
#require no-windows
$ . "$TESTDIR/remotefilelog-library.sh"
$ hg init master
$ cd master
$ cat >> .hg/hgrc <<EOF
> [remotefilelog]
> server=True
> EOF
$ echo x > x
$ hg commit -qAm x
$ echo y >> x
$ hg commit -qAm y
$ echo z >> x
$ hg commit -qAm z
$ echo a > a
$ hg commit -qAm a
$ cd ..
$ hgcloneshallow ssh://user@dummy/master shallow -q
2 files fetched over 1 fetches - (2 misses, 0.00% hit ratio) over *s (glob)
$ cd shallow
Test blame
$ hg blame x
0: x
1: y
2: z
2 files fetched over 1 fetches - (2 misses, 0.00% hit ratio) over *s (glob)
Test grepping the working directory.
$ hg grep --all-files x
x:x
$ echo foo >> x
$ hg grep --all-files x
x:x