The comment was incorrect, claiming that ZTimelineId is a 32-byte value.
It is actually 16 bytes wide. While we're at it, improve the comment,
explaining what a zenith timeline is, and why it's different from
PostgreSQL timelines.
When calling into the page cache, it was possible to wait on a blocking
mutex, which can stall the async executor.
Replace that sleep with a SeqWait::wait_for(lsn).await so that the
executor can go on with other work while we wait.
Change walreceiver_works to an AtomicBool to avoid the awkwardness of
taking the lock, then dropping it while we call wait_for and then
acquiring it again to do real work.
- remove needless return
- remove needless format!
- remove a few more needless clone()
- from_str_radix(_, 10) -> .parse()
- remove needless reference
- remove needless `mut`
Also manually replaced a match statement with map_err() because after
clippy was done with it, there was almost nothing left in the match
expression.
Replay XLOG_XACT_COMMIT and XLOG_XACT_ABORT records in walredo.
Don't wait for lsn catchup before walreceiver connected.
Use 'request_nonrel' branch of vendor/postgres
This replaces the page server's "datadir" concept. The Page Server now
always works with a "Zenith Repository". When you initialize a new
repository with "zenith init", it runs initdb and loads an initial
basebackup of the freshly-created cluster into the repository, on "main"
branch. Repository can hold multiple "timelines", which can be given
human-friendly names, making them "branches". One page server simultaneously
serves all timelines stored in the repository, and you can have multiple
Postgres compute nodes connected to the page server, as long they all
operate on a different timeline.
There is a new command "zenith branch", which can be used to fork off
new branches from existing branches.
The repository uses the directory layout desribed as Repository format
v1 in https://github.com/zenithdb/rfcs/pull/5. It it *highly* inefficient:
- we never create new snapshots. So in practice, it's really just a base
backup of the initial empty cluster, and everything else is reconstructed
by redoing all WAL
- when you create a new timeline, the base snapshot and *all* WAL is copied
from the new timeline to the new one. There is no smarts about
referencing the old snapshots/wal from the ancestor timeline.
To support all this, this commit includes a bunch of other changes:
- Implement "basebackup" funtionality in page server. When you initialize
a new compute node with "zenith pg create", it connects to the page
server, and requests a base backup of the Postgres data directory on
that timeline. (the base backup excludes user tables, so it's not
as bad as it sounds).
- Have page server's WAL receiver write the WAL into timeline dir. This
allows running a Page Server and Compute Nodes without a WAL safekeeper,
until we get around to integrate that properly into the system. (Even
after we integrate WAL safekeeper, this is perhaps how this will operate
when you want to run the system on your laptop.)
- restore_datadir.rs was renamed to restore_local_repo.rs, and heavily
modified to use the new format. It now also restores all WAL.
- Page server no longer scans and restores everything into memory at startup.
Instead, when the first request is made for a timeline, the timeline is
slurped into memory at that point.
- The responsibility for telling page server to "callmemaybe" was moved
into Postgres libpqpagestore code. Also, WAL producer connstring cannot
be specified in the pageserver's command line anymore.
- Having multiple "system identifiers" in the same page server is no
longer supported. I repurposed much of that code to support multiple
timelines, instead.
- Implemented very basic, incomplete, support for PostgreSQL's Extended
Query Protocol in page_service.rs. Turns out that rust-postgres'
copy_out() function always uses the extended query protocol to send
out the command, and I'm using that to stream the base backup from the
page server.
TODO: I haven't fixed the WAL safekeeper for this scheme, so all the
integration tests involving safekeepers are failing. My plan is to modify
the safekeeper to know about Zenith timelines, too, and modify it to work
with the same Zenith repository format. It only needs to care about the
'.zenith/timelines/<timeline>/wal' directories.
For some reason printing the Result made the error string print twice,
along with some annoying newlines. Extracting the error first gets the
expected result (just one explanation, no newlines)
Just a few more places where we can drop the .unwrap() call in favor of
`?`.
Also include a fix to the log file handling: don't open the file twice.
Writing to two fds would result in one message overwriting another.
Presumably `File.try_clone()` reduces down to `dup` on Linux.
This is a first attempt at a new error-handling strategy:
- Use anyhow::Error as the first choice for easy error handling
- Use thiserror to generate local error types for anything that
needs it (no error type is available to us) or will be inspected
or matched on by higher layers.
Resolve some basic warnings from clippy:
- useless conversion to the same type
- redundant field names in struct initialization
- redundant single-component path imports
We don't need the nightly compiler, but there's no reason it shouldn't
compile without warnings, either. I don't know why stable doesn't warn
about these, but it's cheap to suppress them.
Using the hash should allow us to change the remote repo and propagate
that change to user builds without that change becoming visible at a
random time.
It's unfortunate that we can't declare this dependency once in the
top-level Cargo.toml; that feature request is rust-lang rfc 2906.
When postgres sends us a keepalive message, send a reply so it doesn't
time out and close the connection.
The LSN values sent may need to change in the future. Currently we send:
write_lsn <= page_cache last_valid_lsn
flush_lsn <= page_cache last_valid_lsn
apply_lsn <= 0
