It seems that the maxSize parameter will be affected by the running memory of the mobile phone. If the mobile phone is relatively low-end and I create multiple isars to store different functional data, then this error MdbxError (12): Cannot allocate memory will be reported.

I have this issue too. maxSizeMiB: 3072000, changed to default Isar.defaultMaxSizeMiB it works.

But the default size is already specified to Isar.defaultMaxSizeMiB if null, isn't it?

factory _IsarImpl.open({
    required List<IsarGeneratedSchema> schemas,
    required String name,
    required IsarEngine engine,
    required String directory,
    required int? maxSizeMiB,
    required String? encryptionKey,
    required CompactCondition? compactOnLaunch,
    String? library,
  }) {
    IsarCore._initialize(library: library);

    if (engine == IsarEngine.isar) {
      if (encryptionKey != null) {
        throw ArgumentError('Isar engine does not support encryption. Please '
            'set the engine to IsarEngine.sqlite.');
      }

      // look at this line
      maxSizeMiB ??= Isar.defaultMaxSizeMiB;
    } else {
      if (compactOnLaunch != null) {
        throw ArgumentError('SQLite engine does not support compaction.');
      }
      maxSizeMiB ??= 0;
    }

I also wanted to know the meaning of the maxSize. Our size was set to number x and after a while we couldn't write data into the database.

So it could be related to the file size AND memory size. Which is completely wrong in my opinion. Why should the developer set a hard limit for a file size (it's not a log file, which should be limited)? We don't know how many data the user will save. It should grow as much as the device has internal storage.

And the observation, that low end devices will crash, seems to show, that the complete database is also in RAM (like redis or memcache). I don't need this behavior.

It always drills down to the question: what is maxSize for?

I also wanted to know the meaning of the maxSize. Our size was set to number x and after a while we couldn't write data into the database.

So it could be related to the file size AND memory size. Which is completely wrong in my opinion. Why should the developer set a hard limit for a file size (it's not a log file, which should be limited)? We don't know how many data the user will save. It should grow as much as the device has internal storage.

And the observation, that low end devices will crash, seems to show, that the complete database is also in RAM (like redis or memcache). I don't need this behavior.

It always drills down to the question: what is maxSize for?

Agree, this should be a bug that needs to be fixed.