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Could you add a test case with that example that you already posted?

I will have to examinate if I am doing anything special on my side. The following test works:

  fit('regression test for #8772 (increment should be atomic))', async () => {
    Parse.Object.disableSingleInstance();

    Parse.Cloud.beforeSave('Parent', (req) => {});
    Parse.Cloud.beforeSave('Child', async (req) => {
      await req.object.get("parent").increment("num_child").save(null, {useMasterKey:true})
    });

    let parent = await new Parse.Object('Parent').save(null, {useMasterKey:true});
    
    const child = () => new Parse.Object('Child').set("parent",parent).save();

    // add synchronously
    await child()
    await child()
    parent = await parent.fetch();
    expect(parent.get('num_child')).toBe(2);

    // add asynchronously
    await Promise.all(Array.from({length: 40}, () => child()))
    parent = await parent.fetch();

    expect(parent.get('num_child')).toBe(42);

I's be surprised if no atomic test already exists. If there really is none we can add your test in any case. Could you open a PR?

Actually I can't find any. I'll open a PR

Yea even for me the updates are not atomic

Yea even for me the updates are not atomic

Could you elaborate on this? The test passes. Can you provide an example?

Yea even for me the updates are not atomic

Could you elaborate on this? The test passes. Can you provide an example?

Yea i tried as well the test you added is passing.
I am using multiple instances of parse server and there are cases where I am updating the object from all the servers at sa,e time using increment op.
But it seems the increment isn't atomic when using multiple instances.

@RahulLanjewar93 Why could it be working in parse-server tests but not in our own code?

Did you run the test on your own infrastructure?

The increment operation should be sent directly to mongo so therefore it should always be atomic independent of how many instances you are using? I am only using one instance

Yea, increment ops in mongo are atomic.
I had tested it before in my own infrastructure where i was using multiple instances. Currently I am occupied with something else, i'll have a test again and update on the same.

But it seems the increment isn't atomic when using multiple instances.

Although I haven't looked, I doubt that there is anything instance specific in the request that is sent to the DB. Maybe it's a DB issue? Or maybe it's an infrastructure issue where requests are lost, time out, or similar?

Or maybe it is a more complex Parse JS SDK issue where multiple increments / decrements, and object re-fetches in between cause issues with caching? You could add a more complex test to the #8789 where you randomly increment / decrement / re-fetch an object in a loop and check whether the end result is still correct.