The Android SDK includes a tool called zipalign 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 app.
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:
AndroidManifest.xml editor.build.properties. The name of the properties are key.store and 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.zipalign is 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.apkzipalign -c -v 4 application.apkWe encourage you manually run zipalign 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!