IssueTracker

I am able to also reproduce issue #1 now; I've committed a change to the sample project that sets enableMultiInstanceInvalidation() on the DB and adjusts the timing a bit more. After running it for 15 minutes or so I am seeing multiple skipped updates.

My production app uses enableMultiInstanceInvalidation() as well, so this may be a significant factor.

Any thoughts on this one? I mean, it makes JournalMode.TRUNCATE largely useless, unless one has a penchant for random app misbehaviors. I'd like to keep using TRUNCATE, as it avoids certain headaches from WRITE_AHEAD_LOGGING.

To be clear, "batching" does not take care of the missed invalidation notifications. Updates for a table may be spaced hours apart, and in my production app about 5% of notifications are lost, meaning that the user does not see the update until the next one comes in, which may be hours later. It's a chatroom feature, where reliable, timely updates are important.

Also, not setting enableMultiInstanceInvalidation() does not fix the issue, it only changes the timing; notifications go missing regardless of whether I include one process or multiple.

Hi - Sorry, we haven't had the chance to investigate this. I know this might be a lot to ask and thanks for giving us a sample app, but have you try adding a transaction in the invalidation tracker? You can check out Room's source code here: https://cs.android.com/androidx/platform/frameworks/support. There are instructions for cloning the repo, building local artifacts and trying them in your app.

Also what headaches are you trying to avoid from WAL mode?

Thanks for the pointer. I've built Room from source now as you suggested and do see that the problem goes away once I use the transactionality block in InvalidationTracker.mRefreshRunnable for all JournalModes. Don't know why that wasn't done in the first place, it certainly is a misconception to assume that TRUNCATE does not need it.

Regarding headaches from WAL mode:

1. Android's SqliteDatabase runs TRUNCATE transactions effectively serializable due to grabbing exclusive locks right at the start of a transaction, so I can worry less about transactions failing, at the cost of reduced concurrency. My app isn't that heavy on DB ops, so favoring reliability over concurrency makes lots of sense. I'd actually assume that this is true for most Android apps, and that TRUNCATE would make a better default, not fancy WAL.
2. WAL has certain other disadvantages, as pointed out here: https://sqlite.org/wal.html In particular the risk of extended failure from SQLITE_BUSY is high for my app as it has DB connections from two processes (https://sqlite.org/wal.html#busy); of particular concern is the recovery case after a crash, where one process may hold an exclusive lock for an extended period of time at startup, essentially causing the other process to error out without much recourse.

Hope this can be fixed soon in an official build; seems a trivial change.

Yes please! It would be ideal if you can write a test for this though, in the test app specifically: https://cs.android.com/androidx/platform/frameworks/support/+/androidx-master-dev:room/integration-tests/testapp/src/androidTest/java/androidx/room/integration/testapp/test/

Similar to your sample app, open a DB in TRUNCATE mode, have a thread that inserts a lot and another one reading notifications and at the end make sure the amount of notifications received match the amount of items inserted.

just to clarify on #8, we cannot count the number of invalidation events as database might combine them. Instead, we need to make sure latest value is always eventually dispatched.

Seems like it was added here: https://android.googlesource.com/platform/frameworks/support/+/2eb8c31eb44ee4bc4138136b8866847b6e49e5b2 (sorry blame is a mess for us due to the androidx renaming so you need to trace the parents to find the issue).

For testing, I agree it is not great as it only shows as a flake but we have a couple tests stress similar to that and we usually use 10secs (to account for cloud devices). Under normal circumstances (device is not slowed down and db is not locked), it shouldn't take more than ~100ms to get the update after the right (usually much faster). But with virtual device testing, we cannot rely on timing hence we pick large enough numbers (if a virtual device idles for 10 seconds, than that is an infra problem).

It is at least better than nothing and if it flakes, that'll keep bugging us until finding a better solution.

Btw, if you can detect the exact ordering of events that will cause the problem, then we can add package private restricted APIs from the InvalidationTracker to have fine tuned control over them in tests.

oh-oh, I'm sorry to hear that, we definitely don't require you to enter any SSH key password. If anything, only the built-in Git integration in Android Studio will ask you for Github credentials if you use it to push changes to Github. Maybe you have some additional plugin that is asking for it? The Github-based setup downloads the correct Android Studio version needed for the project, but some plugins are installed separately and can persist across IDE installations.

#13 i'm curious what went wrong w/ the Github setup. I don't want to hijack this bug but if you can either file an issue at https://b.corp.google.com/issues/new?component=923725&template=1480355 or directly reach out to me (yboyar at google), I would like to figure out why the setup didn't work for you.

I don't think I will add the test; ultimately I am unfamiliar with AOSP tooling and in particular the test setup for this, so it's an open-ended time commitment, and I already spent too much time on this tiny code problem.

I can still make a PR for the code change that fixes the bug (based on my testing via repro & actual app), but it's so trivial that you might just as well change it yourselves. As I mentioned in #10, the primary concern with the code change would be regressions, which are not captured by the envisioned test anyway, so I'd consider it defensible to go without test. The alternative, no fix, leaves TRUNCATE in a poor state.