Clarify OWNERS use with both directory and matchers
Add a note to the owners plugin documentation clarifying
the use-case where two subdirectories need two different
OWNERS files following one the direcotry-based ownership
and the owner relying on matchers.
Bug: Issue 13406
Change-Id: I36285824b366069789c2043c3c1c1b0d82aecc1c
diff --git a/config.md b/config.md
index b294ae8..6cba6eb 100644
--- a/config.md
+++ b/config.md
@@ -200,7 +200,7 @@
## Example 4 - Owners based on matchers
Often the ownership comes from the developer's skills and competencies and
-cannot be purely defined by the project's directory structure.
+cannot be defined solely by the project's directory structure.
For instance, all the files ending with .sql should be owned and signed-off by
the DBA while all the ones ending with .css by approved by the UX Team.
@@ -235,6 +235,19 @@
(Mister Dba) and the .css files (either John Creative or Matt Designer) have
provided their Code-Review +2 feedback.
+The `add_match_owner_approval` predicate would also honour the OWNERS file
+without matchers, giving, therefore, the possibility of having different ownership
+criteria for different subdirectories. Example: /foo-dir/OWNERS can define a
+directory-based ownership while /bar-dir/OWNERS can rely on matching rules.
+
+__PERFORMANCE NOTE: The predicate `add_match_owner_approval` looks,
+at first sight, more powerful and versatile. However, it may generate a significant
+number of reductions and therefore, impact the Gerrit server performance.
+When used with changes with a high number of files involved, it may even crash
+the Gerrit default `rules.reductionLimit`.
+When not using any matcher in the OWNERS file, prefer the `add_owner_approval`,
+which generates a minimal number of reductions.__
+
## Example 5 - Owners details on a per-file basis
When using the owners with a series of matchers associated to different set of
