# HG changeset patch
# User Boris Feld <boris.feld@octobus.net>
# Date 1542710295 0
# Node ID 300f8564220ff259693d59711e868f1c5c8a426b
# Parent  594e84a2e57455ffa2069c9945e91ca737c74ca7
tags: cache `repo.changelog` access when checking tags nodes

The tags reading process checks if the nodes referenced in tags exist. Caching
the access to `repo.changelog` provides a large speedup for repositories with
many tags.

running `hg perftags` in a large private repository
before: ! wall 0.393464 comb 0.390000 user 0.330000 sys 0.060000 (median of 25)
after:  ! wall 0.267711 comb 0.270000 user 0.210000 sys 0.060000 (median of 38)

diff -r 594e84a2e574 -r 300f8564220f mercurial/localrepo.py
--- a/mercurial/localrepo.py	Tue Nov 20 10:46:20 2018 +0000
+++ b/mercurial/localrepo.py	Tue Nov 20 10:38:15 2018 +0000
@@ -1417,10 +1417,11 @@
             tags, tt = self._findtags()
         else:
             tags = self._tagscache.tags
+        rev = self.changelog.rev
         for k, v in tags.iteritems():
             try:
                 # ignore tags to unknown nodes
-                self.changelog.rev(v)
+                rev(v)
                 t[k] = v
             except (error.LookupError, ValueError):
                 pass