Chrome debug mode is Extremely slow

[anativ]

When chrome debugger is attached realm is extremely slow! makes it unusable for development
Happens both on IOS Simulator / Android Emulator

[dovfrank]

+1

[CodeTitanian]

+1

[alazier]

We know android is very slow. We have seen RPC roundtrip times on the order of ~40ms per operation which would slow things down to a halt for complex apps. Things on iOS should be up to a few orders of magnitude faster though.

[CodeTitanian]

It is extremely slow on iOS.
Basically it can't be used as development is not feasible.

[appden]

@CodeTitanian Are you seeing this on device or in the iOS simulator as well? Can you report what the response times look like for the rpc requests by looking at the Network tab in the Web Inspector? I see them averaging around 1ms.

[anativ]

It seems that every get_property takes ~4ms
The problem is that it seems that I have around ~3000 requests
How can I minimize the get_property requests?

[alazier]

A get_property is made every time you access a property value on one of the objects returned from the Realm apis. For Realm objects accessing any property would trigger this call. For List or Results objects, accessing the length property or accessing objects at a given index would trigger this. I suspect you are looping through a set of objects which could results in multiple get_property calls for each element in your collection.

Probably the best you can do to minimize these calls is to cache any information that is reused. Results.length would be an obvious choice here if you are looping through a results set - storing this in a variable could prevent a call being made for each element. If you are reusing object properties you could also try storing those in a var and reusing that. Another thing you could try doing is calling slice on a Results object and then using the returned JS Array rather than accessing the Results directly. This would essentially cache the length property and batch create objects at every index with the downside that the returned Array will not be updated when objects are changed or added.

Beyond that I'm not sure what else you can do easily. There are internal changes we could make to minimize some of these calls - we may be able to cache some property values internally and possibly even cache object properties or preemptively batch fetch some data. For the cases where performance issues are caused by looping through a set of objects these optimizations could possibly speed things up 2x-5x or more at the cost of added complexity. I'm not sure if this would be enough of a speedup to resolve the issues you guys are seeing.

The other alternative would be re-architect the way we do chrome debugging to do more work in js rather than forwarding all operations over rpc to the core Realm implementation. This would be considerable more work but may be necessary if the optimizations mentioned above are not sufficient. It isn't clear if this will be worth the effort as it seems that ReactNative will be moving away from chrome debugging to other alternatives.

[appden]

It's definitely significantly slower on Android simulators than iOS. I suspect the issue on Android may either be from overhead with the virtual machine networking stack or the passing everything through the JNI.

[krzkaczor]

There should be a note about this behaviour in the documentation. I was making research about using a different mobile database for next project in my company. I almost totally ditched realm react native because I was measuring performance by performance.now (which ofc requires debugger attached) and it was really bad.