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Everything was working fine for a long time. But suddenly the device is getting slower than usual (e.g. apps react slowly when starting an action -- like the RSS reader takes "ages" to open an article). Also, several apps start crashing: force-closes as well as unexpected restarts. Sometimes this even involves some automatic reboot of the device.

Is there anything I can do, besides doing a factory-reset? Preferably it should work on un-rooted devices.

Remark: not all described problems may occur together, so on one device e.g. there might be no automatic reboot involved. Question remains the same, nonetheless.

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Are there any hints when you look at the output of adb logcat? –  ott-- Dec 14 '12 at 12:54
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That's better explained by a developer. I assume there is, but I doubt I could fully interprete the Java stacks from the crash. –  Izzy Dec 14 '12 at 13:55
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See also: What should I do before I try advanced troubleshooting –  Sid Dec 30 '12 at 16:21

4 Answers 4

up vote 21 down vote accepted

A behavour as described above in most cases indicates something's messed up in the system. The most likely candidates here are:

  • Application Cache
  • Dalvik Cache

As you might have guessed already, different solutions are available for rooted devices -- but only few for non-rooted devices, which cannot directly access the Dalvik Cache. So read on below examples until you hit something working for you, or continue to the very end for all options.

rooted and non-rooted devices: remove obsolete apps

Cause of a slow-down might be some app, hogging all resources. Those apps usually can be identified via the "battery consumption" page in Settings. But even if you cannot find it there, it cannot hurt to remove apps you once installed but no longer need (see e.g. Alix' answer).

You can also disable some system apps you don't need (keyword: ). To do so, go to Settings → Applications, select the "All" tab, and walk the list to find those apps. Tap their entry, and you should find a "disable" button. It might be grayed out: if so, you first have to "force stop" the app, and maybe to "uninstall updates", before the "disable" button becomes accessible. Note however, that this possibility will not exist for all system apps. For rooted devices, there are several tools available allowing you to "freeze" or even remove system apps (be very careful with the latter); one famous example is Titanium Backup.

rooted and non-rooted devices: Clear the Application Cache

If you're lucky, it's simply that: the Application Cache got filled/messed up. This can be easily resolved, even on non-rooted devices:

  • With methods available by default on each Android system:
    • From your homescreen, go to Settings → Apps → Manage Apps. Make sure to view All Apps, not Downloaded only
    • Walk the list, open each app, and hit the Clear Cache button
  • Easier method using helper apps: There are several apps available on the Playstore which allow to clean all application's caches at once, so you don't have to walk a long list and do it manually. One example for such an app is 1Tap Cleaner, which also can clean up several other histories like e.g. the browser history

rooted devices: Clear Application Cache and Dalvik Cache

Even more likely for the described case is a messed-up Dalvik Cache -- especially if you tested a lot of apps, permanently installing/uninstalling different ones. So a cleanup of the Dalvik Cache most certainly will solve the situation. As a side effect, it will certainly speed-up things. No negative side-effects are to be expected.

  • Via Custom Recovery
    This is the most effective way and sure to really do the job. This example is based on the ClockworkMod Recovery, which is most widely spread. It should be equivalent with AmonRa Recovery.
    • Boot into recovery mode (how to do this often depends on the device/ROM used. For CyanogenMod users it's most easy: Long-Press the power button, select "Reboot", select "Recovery")
    • Using the Volume controls, select Wipe Cache and approve it using the power button. On the next screen, approve the action the same way. This way you easily clear the Application Cache as described above, all at once, without the need of an extra app.
    • Go to the Advanced menu, select to Clear Dalvik Cache the same way with the Volume and Power keys and approve it.
    • Go back to the main menu, and select Reboot. The next reboot will take longer as usual, so don't worry: Android needs to rebuild the Dalvik Cache, that's completely normal behaviour.
  • Helper apps:
    Several apps offer options to cleanup the Dalvik Cache (e.g. SystemCleanup and Titanium Backup PRO Key ★ root). You can try those; but I'm not sure if one of them really "wipes" the Dalvik Cache. At least for Titanium Backup I know it only removes remains from uninstalled apps (i.e. obsolete Dalvik files).

rooted and non-rooted devices last resort: Factory Reset

If none of the above does solve your problem, there's always the Factory Reset. Basically, this does all the above (wiping Application Cache and Dalvik Cache) -- but it also wipes the /data partition. This means: All your settings and data (except those stored on your sd card) as well as all apps you installed yourself are gone. So be sure to have a good backup before doing this (see e.g. Full Backup of non-rooted devices for how to achieve this).


rooted devices: fstrim

Another reason for slowing things down lies in the storage. A little background for understanding:

On the flash memory used in our devices, each cell can only be written so many times. To prevent capacity loss and wear-out, the flash controller applies an algorithm called "wear leveling" to evenly spread writes across the medium. Of course, to prevent data loss you want to write to "empty places" only (except when explicitly overwriting a file). And here comes the culprit: To speed things up, the file system in most cases only marks files deleted, but doesn't tell the controller about the "freed blocks" -- so it becomes inefficient with time.

Android 4.3 addresses this issue with appropriate fstrim calls, telling the controller once a day which blocks to consider freed. Some ROMs integrated a comparable feature also in earlier versions of Android, mounting file systems with the discard option (so the controller is informed at once on deletes), but this slows down deletes a little. For devices not having addressed this in either of the two ways, it might be worth to take a look at the Lagfix App, which calls fstrim in a user-friendly way for selected partitions. Running that once on a long-used device may speed up writes by a factor of up to 30, and even reads get a little faster.

References:

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Wiping the dalvik cache should be unnecessary unless you're on a new kernel/ROM. Clearing it will just remove ALL those files, which will be recreated (except for uninstalled programs, which Titanium is warning you about). –  NoBugs Apr 8 '13 at 0:31
    
Partly correct. If you often install/uninstall/update apps, the Dalvik cache can get cluttered (as you mention TB, that's why it finds things to cleanup there). There are also reports where some app's Dalvik cache was "broken". Wiping the Dalvik cache forces a clean rebuild, which also "defragments" it. So this can speed up things as well as "fix" some issues. –  Izzy Aug 1 '13 at 9:20
    
I usually reboot my device regularly and uses Greenify app –  sameer Mar 11 at 16:46
    
@user3275057 That's like saying "I regularly ventilate my rooms and use power-safe options on my home devices, but still the floor gets dirty and stuff is standing in the way". While both options are helpful, they miss some essential parts – as explained above: Sometimes you've got to mop the floor and tidy the room :) –  Izzy Mar 11 at 17:04

My HTC One V was getting so slow that I was getting ready to smash it. After trying everything with nothing working, I went through my apps and deleted a few. Apparently the one causing all the trouble was You Don't Know Jack. The second it was off my phone my speed dramatically increased and started functioning normally again. Not sure if this will help anyone else, but on the off-chance it does, I just wanted to let you know.

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Good point. Missed that topic in my answer (updated). –  Izzy Aug 29 '13 at 15:38

I have had very similar problems with my phone. The response I got to my query on the whirlpool forums seemed to have fixed it. (I had apps closing, the keyboard not appearing or closing, etc).

Go to settings > power Untick fastboot.

Power off then on your phone.

This saves a hard reset if it works, which it did with me.

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I've noticed on mine that when I run the Gallery app, things get very very slow for a long while, then eventually start working fine again. I suspect that's because I have a huge number of pictures, and almost never use the Gallery app. I think it may be re-scanning and cataloging in the background or other maintenance-type functions.

I found a similar issue when I was cleaning my call log. Every now and then, I'll scroll back several months and delete log entries from telemarketers or other undesireables. When I do this and go back several months, things can get very slow as well. In this case, I suspect it's because I'm essentially fragmenting a very long log file, and it's trying to clean things up in the background, but while it's doing that, I'm continuing to poke additional holes in it. Again though, if I just wait it out, it seems to resolve itself.

Today I did both, and things got extremely slow for about an hour after I finished. But I just left it alone, and now everything smooth as glass once again.

Sometimes we just need to let the machinery do it's job without fiddling with it, thereby making things worse. :)

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In both of your examples, it's not some file you work on but a database. For the Gallery, the MediaScanner should take care for that once it's triggered (scanning for new media files and updating the database; events triggering this include boot_completed and sdcard_mounted). For your call logs, it's again a database which might be automatically "vacuumized" (i.e. de-fragmented), but that should take seconds at max. Not sure what's slowing things down here that much -- but if it resolves itself, all the better :) –  Izzy Jun 10 '13 at 21:49

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