I am developing a chat app that uses firebase database to store data. The usual approach while developing a chat app is to keep the database nodes synced so that you access the messages offline. So the problem rises when I implement the firebase offline capabilities to keep the data nodes synced. Firebase suggests two required steps for accessing data offline:
Enabling disk persistance
this is enabled according to the documentation by using this line of code (in my case I add it in application class):
FirebaseDatabase.getInstance().setPersistanceEnabled(true);
and
Keeping a node synced
this is enabled by simply adding keepsynced(true) to any databasereference that you wish to keep synced, like this:
ChatNode.keepSynced(true);
What is the difference between the two?
According to the firebase team answers on this site, I deduced that:
1) (Disk persistance) stores the data on the device disk to use them when needed, and data is stored wether you write data or read data.
a) If you write data offline: data is stored on disk and is sent to database when you go online again.
b) If you read data offline: the listener that was read online and was kept in disk and stored, you will be able to read it offline from disk.
2) (keep synced true) will keep a database reference synced in 2 ways:
a) If you are also using (disk persistence) with (keep synced) you will be able to keep data synced on disk ... which seems to be the default behavior of (disk persistence).
b) If you are using (keep synced) alone then you only store to what is known as the app memory.
The problem
I did set both of the methods, but my app is now very laggy and slow and sometimes stops on its own.
The question
If all the things that I said above are true, then would this method of offline capability be a heavy load on my app?
If I kept many listeners synced and set persistence enabled, then would the disk become full of data? Should I clean the data? Is the data on disk cleaned by itself in both methods? Is data cleaned by itself from memory?
I want to avoid the lagging and slow response in my app, thanks for your help.
You are right about your assumptions. If you are using FirebaseDatabase.getInstance().setPersistenceEnabled(true); means that Firebase will create a local copy of your database which also means that every change that is made while you are offline, will be added to a queue. So, as this queue grows, local operations and application startup will slow down. So the speed depends on the dimension of that queue. But rememeber, Firebase is designed as an online database that can work for short to intermediate periods of being disconnected and not as an offline database.
Second, if are using many listeners, don't forget to remove the listener accordingly to the life-cycle of your activity like this:
databaseReference.removeEventListener(valueEventListener);
Related
I wanted to store the specific path in Firebase database (JSON) in local phone storage, not all data at the realtime-Firebase database. Say I have a news-feed path for each user in my Firebase-database and I want to save only the news-feed which is specified for the user instead of loading whole useless data on the local storage of user's mobile.
I read this paragraph from the official Firabase site which mentioned that
The Firebase Real-time Database synchronizes and stores a local copy of the data for active listeners. In addition, you can keep specific locations in sync.
DatabaseReference scoresRef = FirebaseDatabase.getInstance().getReference("scores");
scoresRef.keepSynced(true);
If this is the solution to my question, then I can use this line directly without writing that line
FirebaseDatabase.getInstance().setPersistenceEnabled(true);
Those two bits of code are not really related. They don't do the same thing.
keepSynced(true) effectively keeps a listener active on the given reference, from the moment it's called, for as long as the app is running, so that the local version of the data is always in sync with the remote version on the server.
setPersistenceEnabled(true) just activates local caching of the data read by the SDK. When persistence is enabled, the app can still query data previously read. It takes effect for all data read by the SDK. While persistence is enabled, you can't control which data is cached - all read data is cached up to 10MB max. When the max is reached the oldest data will be evicted from the cache.
According to me the best way will be to parse the Firebase JSON data and map it into an object and then save only data that you need in a local storage (News-feed in your case), and then access it later whenever you need it.
For this, you can use Paper DB as a local storage to store specific data and use it whenever you need to. It stores data as a key value pair so you can access your data with the same key you inserted it with in the database. (Just like shared preferences work).
It stores data as cache in your local storage and uses Kryo serialization framework which is pretty fast for I/O operations.
Or you can also use Room (a google library) with SQLite to achieve this task.
Haven't tried Room but i think it will suite your purpose.
Here's the official documentation for Room
Is it possible that an application's listview updates the data from Firebase without even opening the application?
I am working on a restaurant application which has to work offline, so the user must NOT open the application to get the new menu, rather it must be updated automatically (whenever the user is connected to internet) even if the application isn't opened. Is it possible to be achieved?
I think you're confusing updating the DATA with updating the MENU. A menu is a rendered object - if you're driving it with a listview, naturally it won't be updated when the app isn't running because there's no reason to draw a listview update if the listview isn't being shown.
But you can absolutely update the data, and we do this in News Rush to give the user access to new data while offline, if they were online earlier. Just make sure persistence is enabled and run the same query that drives your listview. Make sure the path/params are identical. Persistence will remember that data and if the user is offline the new menu will still show correctly the next time the app is started.
You should update it outstide the app, but, you can enable offline capabilities,
Enabling Offline Capabilities on Android
FirebaseDatabase.getInstance().setPersistenceEnabled(true);
Firebase apps work great offline and we have several features to make
the experience even better. Enabling disk persistence allows your app
to keep all of its state even after an app restart. We provide several
tools for monitoring presence and connectivity state.
To keep data fresh:
Keeping Data Fresh
The Firebase Realtime Database synchronizes and stores a local copy of
the data for active listeners. In addition, you can keep specific
locations in sync.
DatabaseReference scoresRef =
FirebaseDatabase.getInstance().getReference("scores");
scoresRef.keepSynced(true);
The client will automatically download the
data at these locations and keep it in sync even if the reference has
no active listeners. You can turn synchronization back off with the
following line of code.
scoresRef.keepSynced(false); By default, 10MB of previously synced
data will be cached. This should be enough for most applications. If
the cache outgrows its configured size, the Firebase Realtime Database
will purge data that has been used least recently. Data that is kept
in sync, will not be purged from the cache.
Read more:
Enabling Offline Capabilities on Android
We use Firebase as our database on our Android app. We have 2 types of data:
Static data, which changes rarely (less than once a week).
Dynamic/Live data, which keeps on changing on a second-by-second basis.
We have enabled persistence so users can access the static data even when they are offline. However, doing this causes Firebase to cache the dynamic data as well; which means that, whenever any part of dynamic data is queried, and it has been queried before, the user first receives previously cached, stale data and then gets accurate, live data.
We only want persistence for the data under static references, and not for the data under live references. Is it possible to either:
Have persistence enabled only on a particular reference within the database, so that the live data is never cached?
Maintain 2 completely different database instances of Firebase on android, and have persistence enabled on only one of them?
You can use SYNC feature of Firebase. Just turn it off by adding keepSynced(false) and will do the job.
Brief Description:
Firebase synchronizes and stores a local copy of the data for active listeners. In addition, you can keep specific locations in sync.
Copy
Firebase scoresRef = new Firebase("https://dinosaur-facts.firebaseio.com/scores");
scoresRef.keepSynced(true);
The client will automatically download the data at these locations and keep it in sync even if the reference has no active listeners. You can turn synchronization back off with the following line of code.
Copy
scoresRef.keepSynced(false);
By default, 10MB of previously synced data will be cached. This should be enough for most applications. If the cache outgrows its configured size, Firebase will purge data that has been used least recently. Data that is kept in sync, will not be purged from the cache.
Link
I'm trying to find out how far the offline capabilities of Firebase on Android actually go.
As far as I understand, it should be possible to make the Database "persistent" with FirebaseDatabase.getInstance().setPersistenceEnabled(true);
The documentation reads:
The Firebase Realtime Database stores data returned from a query for use when offline. For queries constructed while offline, the Firebase Realtime Database continues to work for previously loaded data. If the requested data hasn't loaded, the Firebase Realtime Database loads data from the local cache. When we come back online our data will load and reflect the query.
Is this also true when the offline state is beeing forced by goOffline?
In this question the user got an answer from firebase support:
While you can use goOffline() to force the client offline for a long time, performance will deteriorate over time. The Firebase clients will queue intermediate state changes, instead of updating the stored state as the server does.
Does this mean the "local database" isn't actually updated like it would be when offline due to connection loss?
Because most of the time any query or value event listener doesn't come back, onDataChange is never called as is onCanceled (I checked!)
If only the connection is lost, it actually works as advertised, although sometimes with up to a minute delay, which seems to be a problem on its own.
What is then the intention of even offering the goOffline() method if this just stops the interaction with the database completely?
In my implementation the app starts offline, with an anonymous authentication. So in the beginning of course the "local database" will be completely empty. But shouldn't the value events at least fire onDataChanged with an empty datasnapshot?
I tried staying online until I received the anonymous UID and added an empty entry into firebase database, which then is queried/cached. After that if I call goOffline, no more entries can be added and no more queries will be answered.
Similar to the above mentioned question, my plan is to offer the user the option to stay offline, with of course the downside of the build up of stored write events in the local cache (but that shouldn't be that big of a problem as there isn't that much data)
So how can I make this work if even possible at all?
The only thing I can see is to have some different database solution in the beginning for actual offline capabilities which has to be translated & transferred to firebase when the user chooses to go online.
I am planning to switch to Firebase as my local and online database for my Android app. As per the docs, Firebase stores changes to the local database first and then pushed it to the online DB when network is available.
In my app, I would be putting some really sensitive data about the user in the database. So here are my questions,
How secure is the local Firebase database?
How difficult is it for a well-intentioned hacker with the right tools to hack it?
Is it just a simple JSON file like the online database, which anyone with root access can open?
Thanks.
In a general sense, Firebase Realtime Database can be used while offline. However, the expectation is that the app is supposed to be connected most of the time, and changes to the database that happen while offline will be synchronized when it has connectivity. 100% offline use is not really a supported use case, because the canonical data store is on the server.
The local copy of the database is limited to (10MB, at least on Android this is the case). If you intend to write to the database beyond this limit while offline, it will evict part of your cached data to make room for whatever you’re adding. Then, you will no longer be able to read those evicted values until the app goes back online. Worse, managing a growing list of writes to apply when back online is taxing on the app, so you don’t want to plan a lot of writes while offline.
Also, if you have permissions or validations defined for your database, these can only be checked on the server. So, if you’re doing offline writing to your local cache and you no longer have an active listener, you may never know if those writes fail.
Because of these caveats, it’s better not to think of Firebase Realtime Database as an “offline” database. It’s better to think of it as a “synchronized” database that actively syncs to the server while connectivity is present.