Possible perf regression between 10.42.3 and 10.47.0 about realm-swift HOT 6 OPEN

➤ PM Bot commented:

Jira ticket: RCOCOA-2306

from realm-swift.

Do you think you can get the Realm file that reproduces the issue and either share it with us or get a profile to help us understand where the app is spending time? As a temporary workaround you could try shipping a version that doesn't compact the Realm file at launch.

@finnschiermer this is updating from Core 13.20.1 to 13.26.0 - I tried skimming through the changelog entries and there was nothing that jumped at me as having potentially large performance impact.

from realm-swift.

As a temporary workaround you could try shipping a version that doesn't compact the Realm file at launch.

How do you do this? Will the realm never be compacted, or just not while it's being opened?

Do you think you can get the Realm file that reproduces the issue and either share it with us or get a profile to help us understand where the app is spending time?

I won't be able to get the exact realm file. We'll likely need to see whether we can create one artificially.

from realm-swift.

You can return false in the shouldCompactOnLaunch callback skipping compaction for the Realm file. You can also use a heuristic where it returns true for smaller files, but not for those large ones, which take a long time.

In terms of whether the file it'll compact, the answer is yes-ish. By that, I mean, that we now have automatic compaction enabled on every commit where we'll do certain cheap storage optimizations continuously. This is not as effective as running a compact on launch but it gets close in a lot of scenarios.

Alternatively, you could restructure your app so that it doesn't open the Realm file as part of the AppDelegate.application call and instead do it after that the app has loaded (possibly adding a loading indicator in case the file size is beyond a certain threshold).

from realm-swift.

Ok, I spoke with @finnschiermer and there's nothing obvious that would cause significant performance degradation between these versions of Core. It's possible that this was already fairly slow and a small write performance regression just pushed it over the 17 seconds limit. If you can provide a repro case, we can run a profile and try to see what's taking more time now.

That being said, compacting such a large file on app initialization would be a bad idea, regardless of the version of the SDK as it would require write speeds of >270 MB/s in the worst case scenario to fit in under 17s, and even then it would be a bad user experience to stare at a blank screen for so long. As suggested above, one approach would be disable compact on launch for files above a certain threshold or if you need to run it, you should try and open the Realm on a background thread after the app has finished initializing, then after that has succeeded, open it on the main thread.

from realm-swift.