# Optimize notmuch's performance
+[[!toc levels=2]]
+
## Xapian 1.2.x database format: chert vs. flint
Xapian 1.2 (in contrast to 1.0.x) uses a new database format called
* [Pieter Praet](http://notmuchmail.org/pipermail/notmuch/2011/004175.html)
+
+## Tagging: use filters!
+
+Instead of just:
+
+ $ notmuch tag +foo
+
+use:
+
+ $ notmuch tag +foo -- not tag:foo
+
+See the ongoing discussion:
+
+* [Optimization for notmuch tag by implicit filters](http://notmuchmail.org/pipermail/notmuch/2011/004197.html)