If gem install fails on this gem (e.g. missing sasl2 devel libraries), correcting the original problem and reinstalling the gem will always fail because the patches against memcached don't apply cleanly and extconf.rb barfs. You have to delete the entire partially-build gem directory and reinstall for things to work. It would be better if extconf.rb either didn't try to apply the patches again, or detected the already-applied case and didn't abort.
If gem install fails on this gem (e.g. missing sasl2 devel libraries), correcting the original problem and reinstalling the gem will always fail because the patches against memcached don't apply cleanly and extconf.rb barfs. You have to delete the entire partially-build gem directory and reinstall for things to work. It would be better if extconf.rb either didn't try to apply the patches again, or detected the already-applied case and didn't abort.