The layered_repository.rs file had grown to be very large. Split off
the LayeredTimeline struct and related code to a separate source file to
make it more manageable.
There are plans to move much of the code to track timelines from
tenant_mgr.rs to LayeredRepository. That will make layered_repository.rs
grow again, so now is a good time to split it.
There's a lot more cleanup to do, but this commit intentionally only
moves existing code and avoids doing anything else, for easier review.
download operations of all timelines for one tenant are now grouped
together so when attach is invoked pageserver downloads all of them
and registers them in a single apply_sync_status_update call so
branches can be used safely with attach/detach
The SyncQueue consisted of a tokio mpsc channel, and an atomic counter
to keep track of how many items there are in the channel. Updating the
atomic counter was racy, and sometimes the consumer would decrement
the counter before the producer had incremented it, leading to integer
wraparound to usize::MAX. Calling Vec::with_capacity(usize::MAX) leads
to a panic.
To fix, replace the channel with a VecDeque protected by a Mutex, and
a condition variable for signaling. Now that the queue is now
protected by standard blocking Mutex and Condvar, refactor the
functions touching it to be sync, not async.
A theoretical downside of this is that the calls to push items to the
queue and the storage sync thread that drains the queue might now need
to wait, if another thread is busy manipulating the queue. I believe
that's OK; the lock isn't held for very long, and these operations are
made in background threads, not in the hot GetPage@LSN path, so
they're not very latency-sensitive.
Fixes#1719. Also add a test case.
Try to follow Prometheus style-guide https://prometheus.io/docs/practices/naming/ for metrics names. More specifically:
- Use `pageserver_` prefix for all pagserver metrics
- Specify `_seconds` unit in time metrics
- Use unit as a suffix in other cases, such as `_hits`, `_bytes`, `_records`
- Use `_total` suffix for accumulating counters (note that Histograms append that suffix internally)
