* `wal_acceptor`: add HTTP handler, /metrics endpoint only, no authentication
* Two gauges are currently reported: `flush_lsn` and `commit_lsn`
* Add `DEFAULT_PG_LISTEN_PORT` and `DEFAULT_PG_LISTEN_PORT` consts for uniformity
The caller is now responsible for lookin up the predecessor layer,
instead. This makes the code simpler, as you don't need to update the
predecessor reference when a layer is frozen or written to disk.
There was a bug in that, as Konstantin noted on discord:
Assume that freeze doesn't create new inmem layer
(maybe_new_open=None). Then we temporary place in historics frozen
layer. Assume that now new put_wal_record request arrives. There is
no open in-mem layer, so it has to create new one. It is looking for
previous layer for read and set it as new in-mem layer
predecessor. But as far as I understand, prev layer should be our
temporary frozen layer. Which will be then removed from
historics.
That leaves the predecessor field of the new in-memory layer pointing
at the frozen in-memory layer that has been removed from the layer map,
preventing it from being removed from memory.
This makes two subtle changes:
1. When the first new layer is created on a branch for a segment that
existed on the ancestor branch, the start_lsn of the new layer is now
the branch point + 1. We were previously slightly confused on what
the branch point LSN meant. It means that all the WAL up to and
*including* the LSN on the old branch is visible to the new branch.
If we mark the start LSN of the new layer as equal to the branch point,
that's wrong, because if there is a WAL record with that LSN on the
predecessor layer, the new layer would hide it. This bug was hidden
when the layer on the new branch contained a direct reference to the
layer in the old branch, as get_page_reconstruct_data() followed that
reference directly when it didn't find the page version in the new
layer. But now that the caller performs the lookup, it will look up
the new layer that doesn't contain the record, and you get an error.
2. InMemoryLayer now always stores the segment size at the beginning
of the layer's LSN range. Previously, get_seg_size() might have
recursed into the predecessor layer to get the size, but now we
avoid that by always copying over the last size from the previous
layer, when a new layer is created.
The dockerignore and dockerfile have also been excluded from being moved into
docker images, saving docker layer cache busts if only those are changed.
Commit ca9af37478 removed the import_timeline_wal() call from here.
After that, the info!() message is bogus, as we no longer load the WAL
from local disk. Also, the logical size assertion is pointless now.
All the changes are in the vendor/postgres side. However, because we now
generate fewer Full Page Writes, the 'branch_behind' test needs to be
modified so that it still generates enough WAL to consume a few WAL
segments.
The metadata file is now always 512 bytes. The last 4 bytes are a
crc32c checksum of the previous 508 bytes. Padding zeroes are added
between the serde serialization and the start of the checksum.
A single write call is used, and the file is fsyncd after.
On file creation, the parent directory is fsyncd as well.
It previously took &SafeKeeperState similar to persist(), but only for its
`server` member.
Now it takes &ServerInfo only, so there it's clear the state is not persisted.
Also added a comment about sync.
* Send ProposerGreeting manually in tests
* Move test_sync_safekeepers to test_wal_acceptor.py
* Capture test_sync_safekeepers output
* Add comment for handle_json_ctrl
* Save captured output in CI
