view docs/evolve-good-practice.rst @ 1363:2eaa2943f9f3

directaccess: use cached filteredrevs

Before this patch we were calling directly repoview.computehidden(repo) to
compute the revisions visible with direct access, without going through the
caching mechanism for the filtered revisions.

There was two issues with that:
(1) Performance: We were not leverating the cached values of the 'visible' revs
(2) Stability: If there were to be a cache inconsistency with the computation of
'visible' we would crash in the branchmap consistency check partial.validfor.
Consider the scenario of rebase with bookmarks:
- when we delete a bookmark on an obsolete changeset (like what rebase
  does when moving the bookmark after rebasing the changesets)
- then this changes the value returned by repoview.computehidden(repo) as
  bookmarks are used as dynamic blockers in repoview.computehidden(repo)
- as of now, we don't invalidate the cache in the case of bookmark change
- if we have a cached value from before the bookmark change,
  repoview.filterrevs(repo, 'visible') considers the cached value correct and
  returns something different than repoview.computehidden(repo)
- in turn, if we use repoview.computehidden(repo) in directaccess, the subset
  relationship is broken and the cache consistency assertion (parial.validfor)
  fails if branchmap.updatecache is called in this time window

This patch leverages the caching infrastructure in place to speed up the
computation of the filteredrevs for visible-directaccess-nowarn and
visible-directaccess-warn. Incidentally it prevents the bug discussed in (2)
from crashing when running a rebase with a bookmark. Note that there still
needs to be a fix in core for the case discussed in (2).

The test for this side of the fix (not core's fix for (2) is very hard to
implement without introducing a lot of dependencies and does not belong
here. It is much easier to have the test of the fix for the scenario (2) in
core along with the fix.

.. Copyright 2011 Pierre-Yves David <[e-mail]>
..                Logilab SA        <[e-mail]>

-----------------------------------------
Good practice for (early) users of evolve
-----------------------------------------

Avoid unstability
-----------------

The less unstability you have the less you need to resolve.

Evolve is not yet able to detect and solve every situation. And your mind is
not ready neither.

Branch as much as possible
--------------------------

This is not MQ; you are not constrained to linear history.

Making a branch per independent branch will help you avoid unstability
and conflict.

Rewrite your changes only
-------------------------

There is no descent conflict detection and handling right now.
Rewriting other people's changesets guarantees that you will get
conflicts. Communicate with your fellow developers before trying to
touch other people's work (which is a good pratice in any case).

Using multiple branches will help you to achieve this goal.

Prefer pushing unstability to touching other people changesets
--------------------------------------------------------------


If you have children changesets from other people that you don't really care
about, prefer not altering them to risking a conflict by stabilizing them.


Do not get too confident
------------------------

This is an experimental extension and a complex concept. This is beautiful,
powerful and robust on paper, but the tool and your mind may not be prepared for
all situations yet.