Out Of Memory Error

[IndianaSloan]

I am receiving a crash on Crashlytics with the following exception:

Fatal Exception: io.realm.exceptions.RealmError: Unrecoverable error. mmap() failed: Out of memory size: 2147483648 offset: 0 in /Users/cm/Realm/realm-java-release/realm/realm-library/src/main/cpp/io_realm_internal_OsSharedRealm.cpp line 101

I understand this issue has been raised before a few times, however I have researched through all of the possible suggestions and cannot find a solution to this crash. This is an app in production for several years and this crash has only started to happen recently. It happens to less than 1% of my users but ironically it is only happening on one specific device - Samsung Galaxy Tab A SM-T510.

The crash seems to be happening on launch of the app, when trying to get an instance of Realm, rather than when trying to execute a transaction, or perform any other operation. The database size varies in different crashes, they are one of the following:

• 2147483648
• 2013265920
• 1476395008
• 1342177280
• 1207959552

Steps I have taken to try and solve:

• I have ensured all open instances of realm are closed as soon as I am finished with them
• I have checked that all transactions are not inside long loops
• I have attempted to migrate Realm to a new version, and delete all of the database

Actual Results

Fatal Exception: io.realm.exceptions.RealmError: Unrecoverable error. mmap() failed: Out of memory size: 2147483648 offset: 0 in /Users/cm/Realm/realm-java-release/realm/realm-library/src/main/cpp/io_realm_internal_OsSharedRealm.cpp line 101 at io.realm.internal.OsSharedRealm.nativeGetSharedRealm(OsSharedRealm.java) at io.realm.internal.OsSharedRealm.<init>(OsSharedRealm.java:171) at io.realm.internal.OsSharedRealm.getInstance(OsSharedRealm.java:241) at io.realm.internal.OsSharedRealm.getInstance(OsSharedRealm.java:231) at io.realm.RealmCache.doCreateRealmOrGetFromCache(RealmCache.java:318) at io.realm.RealmCache.createRealmOrGetFromCache(RealmCache.java:284) at io.realm.Realm.getDefaultInstance(Realm.java:407) at com.myapp.android.app.MyApp.initializeIntercom(MyApp.java:215) at com.myapp.android.app.MyApp.onCreate(MyApp.java:117) at android.app.Instrumentation.callApplicationOnCreate(Instrumentation.java:1158) at android.app.ActivityThread.handleBindApplication(ActivityThread.java:6272) at android.app.ActivityThread.access$1200(ActivityThread.java:240) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1796) at android.os.Handler.dispatchMessage(Handler.java:106) at android.os.Looper.loop(Looper.java:214) at android.app.ActivityThread.main(ActivityThread.java:7100) at java.lang.reflect.Method.invoke(Method.java) at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:494) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:964)

Steps & Code to Reproduce

I have been unable to reproduce this crash. I have also inflated Realm on my own device to 2.45GB by inserting dummy data, and have yet been unable to reproduce. I have detailed below the function in my Application class where the crash happens.

private void initializeIntercom() {
        String intercomIdCheck = getString(R.string.intercom_api_id);
        String intercomKeyCheck = getString(R.string.intercom_api_key);
        if (intercomIdCheck.isEmpty() || intercomKeyCheck.isEmpty()) {
            return;
        }

        Realm realm = null;

        try {
            realm = Realm.getDefaultInstance(); <------ LINE 215 where crash happens

            User user = realm.where(User.class)
                    .equalTo("userId", datastore.getUserId())
                    .findFirst();
            if (user != null &&
                    user.settings != null &&
                    user.settings.intercom_enabled == 1) {
                Intercom.initialize(
                        this,
                        getString(R.string.intercom_api_key),
                        getString(R.string.intercom_api_id)
                );
            }
        } catch (Exception ex) {
            MyApp.logThrowable(ex);
        } finally {
            if (realm != null) {
                realm.close();
            }
        }
    }

Version of Realm and tooling

Realm version(s): 5.12.0

Realm Sync feature enabled: No

Android Studio version: 3.5.3

Android Build Tools version: 28

Gradle version: 5.4.1

Which Android version and device(s): Android 9 - Samsung Tab A SM-T510

[sdex]

It's something wrong with this device. I've got a lot of OOM crash reports from this particular device too. The realm file is huge.

Fatal Exception: io.realm.exceptions.RealmError: Unrecoverable error. mmap() failed: Out of memory size: 503316480 offset: 0 in /Users/cm/Realm/realm-java-release/realm/realm-library/src/main/cpp/io_realm_internal_OsSharedRealm.cpp line 101
       at io.realm.internal.OsSharedRealm.nativeGetSharedRealm(OsSharedRealm.java)
       at io.realm.internal.OsSharedRealm.<init>(OsSharedRealm.java:171)
       at io.realm.internal.OsSharedRealm.getInstance(OsSharedRealm.java:241)
       at io.realm.internal.OsSharedRealm.getInstance(OsSharedRealm.java:231)
       at io.realm.RealmCache.doCreateRealmOrGetFromCache(RealmCache.java:318)
       at io.realm.RealmCache.createRealmOrGetFromCache(RealmCache.java:284)
       at io.realm.Realm.getDefaultInstance(Realm.java:407)

Galaxy Tab A (gt510wifi) - Android 7.1
Galaxy Tab A (2017) (gta2slte) - Android 9

[nhachicha]

@IndianaSloan the reported size is > 2G, are you expecting such volume of data? is this a normal usage? you can try to compact the Realm to see if this helps on this device

[IndianaSloan]

Thanks for the suggestions @nhachicha , the size could potentially get this size over time, as I'm not ever clearing data. I have tried contracting realm, and also migrating realm to a new version and wiping realm. Yet still experiencing this crash

[rubnov]

I'm experiencing the exact same issue and have gone through the same steps to ensure that no realm instances are left open on background threads. The number of global instances is 1, occasionally rising to 2 and back to 1 as background threads close their Realm instances.

The issue occurs when the app is launched to the background and on the first call to Realm.getDefaultInstance():

98% if the crashes occurred when the app launched to the background. However, it happens to only a a handful our users (<10) and only on a few devices, namely:

• Samsung Galaxy A10 (Android 10)
• Samsung J4+ (Android 8.1.0)

I am not sure, however, that this suggests a device-specific issue. It could well be that the crash has so far occurred on these devices / to these users only because the Realm DB for their account has bloated to a very large size.

Here is the code where the crash occurs:

public class PSApplicationClass extends Application implements BeaconConsumer, RequestQueue.RequestFinishedListener {
...
    @Override
    public void onCreate() {
        super.onCreate();
        singleton = this;
        try {

            mRequestQueue = Volley.newRequestQueue(PSApplicationClass.this);
            mRequestQueue.addRequestFinishedListener(PSApplicationClass.this);
            pref = new PassengerPreferencesManager(this);

            Realm.init(PSApplicationClass.this);
            Config = new RealmConfiguration.Builder()
                    .name("myrealm.realm")
                    .schemaVersion(5)
                    .migration(new Migration())
                    .compactOnLaunch(new CompactOnLaunchCallback() {
                        @Override
                        public boolean shouldCompact(long totalBytes, long usedBytes) {
                            // Compact if the file is over 500KB in size and less than 20% 'used'
                            boolean should = (totalBytes > LARGE_REALM_FILE) && (usedBytes / (double) totalBytes) < 0.2;
                            String msg = "Realm totalSize " + totalBytes + " usedBytes " + usedBytes;
                            Utils.appendLog(msg, "I", Constants.REALM);
                            FirebaseCrashlytics.getInstance().log(msg);
                            return should;
                        }
                    })
                    .build();

            Realm.setDefaultConfiguration(Config);

            Realm realm = Realm.getDefaultInsance();  // <-- crashes here!

The specific error info in the crash report is:

Fatal Exception: io.realm.exceptions.RealmError
Unrecoverable error. mmap() failed: Out of memory size: 1879048192 offset: 0 in /Users/cm/Realm/realm-java-release/realm/realm-library/src/main/cpp/io_realm_internal_OsSharedRealm.cpp line 101

Sizes in the above message vary from 1GB (e.g. 1073741824) to 2GB.

As seen in my code sample above, I am compacting the DB on launch. However, I am unsure as to whether this is done synchronously or asynchronously, or if there is a way to ensure that compactOnLaunch() has finished before attempting to call Realm.getDefaultInstance(). I am also unsure of how compactOnLaunch() reports success/failure.

[rubnov]

Can anyone help resolve this issue?

As mentioned, this mmap() RealmError occurs on app launch. There are no open Realm instances or Realm objects retained in memory at this point, and the first call to Realm.getDefaultInstance() produces this crash.

Worthy to note: I have simplified the code sample above with regards to obtaining a Realm instance. The actual getDefaultInstance() call is done via a wrapper/manager like this:

public class RealmManager {
    private volatile static LongSparseArray<Realm> THREAD_INSTANCES = new LongSparseArray<>();

    /**
     * Gets instance.
     *
     * @return the instance
     */
    public static Realm getInstance() {
        final long threadId = Thread.currentThread().getId();
        String logMsg = null;
        Realm instance = null;
        if (THREAD_INSTANCES.indexOfKey(threadId) >= 0) {
            instance = THREAD_INSTANCES.get(threadId);
            if (instance == null || instance.isClosed()) {
                checkDefaultConfiguration();
                THREAD_INSTANCES.remove(threadId);
                instance = Realm.getDefaultInstance();

                THREAD_INSTANCES.put(threadId, instance);
                logMsg = "RealmManager getInstance (recycled) thread " + threadId + " " + Utils.getCallingMethodName() + ". Number of Realm instances: " + THREAD_INSTANCES.size() + "(" + Realm.getGlobalInstanceCount(instance.getConfiguration()) + ")";
            }
        } else {
            instance = Realm.getDefaultInstance();   // <-- crashes here
            THREAD_INSTANCES.put(threadId, instance);
            logMsg = "RealmManager getInstance (new) thread " + threadId + " " + Utils.getCallingMethodName() + ". Number of Realm instances: " + THREAD_INSTANCES.size() + "(" + Realm.getGlobalInstanceCount(instance.getConfiguration()) + ")";
        }

        if (logMsg != null) {
//            Utils.appendLog(logMsg, "D", Constants.REALM);
            FirebaseCrashlytics.getInstance().log(logMsg);
        }
        return instance;

    }

    /**
     * Close instance.
     */
    public static void closeInstance() {
        long threadId = Thread.currentThread().getId();

        if (THREAD_INSTANCES.indexOfKey(threadId) >= 0) {
            Realm instance = THREAD_INSTANCES.get(threadId);

            if (instance == null || instance.isClosed()) {
                THREAD_INSTANCES.remove(threadId);
                String logMsg = "RealmManager closeInstance (removed) thread " + threadId + " " + Utils.getCallingMethodName() + ". Number of Realm instances: " + THREAD_INSTANCES.size();
            } else {
                instance.close();
                THREAD_INSTANCES.remove(threadId);
                String logMsg = "RealmManager closeInstance (closed) thread " + threadId + " " + Utils.getCallingMethodName() + ". Number of Realm instances: " + THREAD_INSTANCES.size();
//                Utils.appendLog(logMsg, "D", Constants.REALM);
                FirebaseCrashlytics.getInstance().log(logMsg);
            }
        }
    }

So in fact the first call to RealmManager.getInstance(), made from ApplicationClass.onCreate() when the app launches, crashes the app on the line Realm.getDefaultInstance().

This only occurs on a handful of devices, as mentioned above, and is not the general case. Here is the error info:

Fatal Exception: io.realm.exceptions.RealmError
Unrecoverable error. mmap() failed: Out of memory size: 2013265920 offset: 0 in /Users/cm/Realm/realm-java-release/realm/realm-library/src/main/cpp/io_realm_internal_OsSharedRealm.cpp line 101

[rorbech]

@rubnov Can you share some details on the version of Realm and whether you have sync enabled? We are currently investigating another crash that could be related to apps starting in background and compacting in #6889

[rubnov]

    dependencies {
        classpath "io.realm:realm-gradle-plugin:5.15.1"
        ...
    }

We are not using Realm Sync. We have a local Realm db within the app.

[cmelchior]

@rubnov Are you still using 5.15.1? Is it possible for you to upgrade to 7.0.2? We added some improvements to how we memory map files there which might help solve issues like this.

Before 7.0, we had to map the entire Realm file in one continuous region. This was a problem for large files. Especially if the virtual address space was fragmented. With 7.0 we can now do this in 64 MB blocks.

[rubnov]

Updated Realm plugin to 7.0.2 but still getting this error.

Device info: Samsung Galaxy A10
RAM free: 410.47 MB
Disk free: 1.11 GB
Android 10

Error getting Realm instance: Unrecoverable error. mmap() failed: Out of memory size: 1879048192 offset: 0 in /Users/cm/Realm/realm-java/realm/realm-library/src/main/cpp/io_realm_internal_OsSharedRealm.cpp line 107

Again, this happens immediately on launch, in ApplicationClass.onCreate() when calling Realm.getDefaultInstance() for the first time and from the main thread.

[cmelchior]

So the Realm you are trying to open 1.8GB. I don't know if your Realm contains that much data, but usually when they get this big it normally points to problems controlling the Realm life cycle which can inflate the file size.

You can read more here:
https://realm.io/docs/java/latest/#faq-large-realm-file-size
https://realm.io/docs/java/latest/#realm-instance-lifecycle
https://realm.io/docs/java/latest/#closing-realms

[rubnov]

Our app runs for extended periods in the background, and keeps a single realm instance (that of the main thread) alive all the time. Is this the cause of the bloating up of the database? If so - it is a serious design flaw in Realm library.

Why is keeping a Realm instance in memory causing the Realm database file to grow indefinitely and disproportionally? Is this caused by the "versioning" of Realm objects? Is there a way to configure Realm NOT to keep multiple versions of objects?

In order to work around this Realm by-design limitation, I would have to refactor the entire app code base to close Realm instances on a function, Fragment or Activity boundaries. This would cost me weeks of work. Very frustrating!

[cmelchior]

It should be fine to keep Realms open on threads with Loopers, like the main thread. Those are automatically kept up to date. You can read more about that here: https://academy.realm.io/posts/threading-deep-dive/

So if you are experiencing bloat it must happen for some other reason, but without seeing the code, it is hard to speculate why

Note, there are number of methods that can be used to debug things like this.

https://realm.io/docs/java/10.0.0/api/io/realm/RealmConfiguration.Builder.html#maxNumberOfActiveVersions-long-
https://realm.io/docs/java/10.0.0/api/io/realm/Realm.html#getGlobalInstanceCount-io.realm.RealmConfiguration-
https://realm.io/docs/java/10.0.0/api/io/realm/Realm.html#getLocalInstanceCount-io.realm.RealmConfiguration-

[rubnov]

OMG, I've just found out that Realm still does not support cascading deletes. This means that when a RealmObject is deleted, all the objects related to it (e.g. within RealmList propereties) are NOT deleted ?!?!?