The Android SDK includes a tool called
that optimizes the way an application is packaged. Running zipalign against your
application enables Android to interact it more efficiently at run time and thus
has the potential to make it and the overall system run faster. We strongly
encourage you to use
zipalign on both new and already published
applications and to make the optimized version available — even if your
application targets a previous version of Android. This article describes how
zipalign helps performance and how to use it to optimize your
In Android, data files stored in each application's apk are accessed by multiple processes: the installer reads the manifest to handle the permissions associated with that application; the Home application reads resources to get the application's name and icon; the system server reads resources for a variety of reasons (e.g. to display that application's notifications); and last but not least, the resource files are obviously used by the application itself.
The resource-handling code in Android can efficiently access resources when
they're aligned on 4-byte boundaries by memory-mapping them. But for resources
that are not aligned (that is, when
zipalign hasn't been run on an
apk), it has to fall back to explicitly reading them — which is slower and
consumes additional memory.
For an application developer, this fallback mechanism is very convenient. It provides a lot of flexibility by allowing for several different development methods, including those that don't include aligning resources as part of their normal flow.
Unfortunately, for users the situation is reversed — reading resources from unaligned apks is slow and takes a lot of memory. In the best case, the only visible result is that both the Home application and the unaligned application launch slower than they otherwise should. In the worst case, installing several applications with unaligned resources increases memory pressure, thus causing the system to thrash around by having to constantly start and kill processes. The user ends up with a slow device with a poor battery life.
Luckily, it's very easy for you to align the resources in your application:
build.properties. The name of the properties are
key.aliasrespectively. If those properties are present, the signing tool will prompt to enter the store/key passwords during the build, and the script will sign and then align the apk file. If the properties are missing, the release package will not be signed, and therefore will not get aligned either.
zipalignis in the
tools/folder of Android 1.6 and later SDKs. You can use it to align application packages targeting any version of Android. You should run it only after signing the apk file, using the following command:
zipalign -v 4 source.apk destination.apk
zipalign -c -v 4 application.apk
We encourage you manually run
on your currently published applications and to make the newly aligned
versions available to users. Also, don't forget to align any new
applications going forward!