[Replay] Improve Missing Segments

[JoshFerge]

From experimentation, here are some things we can do to improve our missing segments problem:

• Flush more often based on the size of the buffer. if we keep requests under 64kB, we can use sendBeacon more, and overall smaller segments will be more reliable for sending. We can add an event / listener based on buffer size.
• Don't wait to flush on initializing. Flush immediately. This should help with us missing 0 segments on replays. We can always filter out short replays query side.

[bruno-garcia]

Relates to: #6502

[jas-kas]

Note: should see a new report on numbers of segment quality, breakdown by SDK version

[billyvg]

As an update we're going to flush more often based on timing (previously we were waiting up to 15 seconds before flushing, but we plan to decrease this to 5 seconds as max wait). Aside from the initial segment, the incremental ones should remain under 64KB.

The problem that we have is when the page unloads (e.g. when refreshing). We are not able to fetch from our compression worker before the page reloads. You can test this by saving/logging the segment id after sendReplay() call inside of runFlush and comparing it to the session id in start(). Ideally these two values would be the same.

Also with compression, if you had a log statement after await this.eventBuffer.finish(), it will not get called when refreshing. Contrast this with turning compression off, it should run until after the sendReplay() call. (Although right now, the ingest backend sends 400 for some uncompressed payloads).

[Lms24]

Going to assign myself as well here, while I'm working on retrying rate-limited replay requests.

[github-actions]

This issue has gone three weeks without activity. In another week, I will close it.

But! If you comment or otherwise update it, I will reset the clock, and if you label it Status: Backlog or Status: In Progress, I will leave it alone ... forever!

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"A weed is but an unloved flower." ― Ella Wheeler Wilcox 🥀

[billyvg]

We've improved missing segments from 7% to under 1%, so going to close this out for now. Let's open a new ticket if we need to further improve this metric.

There are some other ideas to improve lost segments due to page refreshes/navigation, but they're on hold/closed for now:
#6854
#6698