Perform the whole sync (pull + push) within a single transaction

[n1k0]

So we can abort the whole import process on error, avoiding leaving the db in an inconsistent state.

[michielbdejong]

Not sure if this is relevant here, but just wanted to mention how important batching together writes to IndexedDB is, for performance. This is also a topic in localForage, we are trying to do automatic batching of writes there. The basic principle of that is:

• you add or update one record -> it starts updating IndexedDB
• you add or update more records -> it queues them up until IndexedDB is idle
• the first transaction completes -> it creates a new batch transaction from everything that was added to the queue in the meantime

[n1k0]

After a quick discussion with @ametaireau, here's the current state of our thinking on this:

• Having transactions would provide a neat way to cancel local persistence operations;
• It would also improve performances on large batches of persistence operations;
• localStorage adapter would need a specific manually implemented solution to cover all the use cases;
• We should heavily challenge if we actually need this feature: for now, nobody has explicitly expressed a need for it;
• We should also discuss this with @leplatrem which I remember was having opinions on the matter.

Thoughts?

[n1k0]

#303 has now landed and is a huge step towards this goal.

[leplatrem]

When https://bugzilla.mozilla.org/show_bug.cgi?id=1193394 will land in Firefox, it will be possible to have IndexedDB transactions across promises in Chrome+Firefox.

[leplatrem]

That's it! It landed!

Firefox 60 supports promises within IndexedDB transactions \o/

There is a lot of things that could be simplified, quite a huge amount of work.

[michielbdejong]

Wow! :)