fixes https://github.com/zrepl/zrepl/issues/742
Before this PR, when chaining replication from
A => B => C, if B had placeholders and the `filesystems`
included these placeholders, we'd incorrectly
fail the planning phase with error
`sender does not have any versions`.
The non-placeholder child filesystems of these placeholders
would then fail to replicate because of the
initial-replication-dependency-tracking that we do, i.e.,
their parent failed to initially replication, hence
they fail to replicate as well
(`parent(s) failed during initial replication`).
We can do better than that because we have the information
whether a sender-side filesystem is a placeholder.
This PR makes the planner act on that information.
The outcome is that placeholders are replicated as
placeholders (albeit the receiver remains in control
of how these placeholders are created, i.e., `recv.placeholders`)
The mechanism to do it is:
1. Don't plan any replication steps for filesystems that
are placeholders on the sender.
2. Ensure that, if a receiving-side filesystem exists, it
is indeed a placeholder.
Check (2) may seem overly restrictive, but, the goal here
is not just to mirror all non-placeholder filesystems, but
also to mirror the hierarchy.
Testing performed:
- [x] confirm with issue reporter that this PR fixes their issue
- [x] add a regression test that fails without the changes in this PR
Go 1.18 deprecated net.Error.Temporary().
This commit cleans up places where we use it incorrectly.
Also, the rpc layer defines some errors that implement
interface { Temporary() bool }
I added comments to all of the implementations to indicate
whether they will be required if net.Error.Temporary is ever
ever removed in the future.
For HandshakeError, the Temporary() return value is actually
important. I moved & rewrote a (previously misplaced) comment
there.
The ReadStreamError changes were
1. necessary to pacify newer staticcheck and
2. technically, an error can implement Temporary()
without being net.Err. This applies to some syscall
errors in the standard library.
Reading list for those interested:
- https://github.com/golang/go/issues/45729
- https://groups.google.com/g/golang-nuts/c/-JcZzOkyqYI
- https://man7.org/linux/man-pages/man2/accept.2.html
Note: This change was prompted by staticheck:
> SA1019: neterr.Temporary has been deprecated since Go 1.18 because it
> shouldn't be used: Temporary errors are not well-defined. Most
> "temporary" errors are timeouts, and the few exceptions are surprising.
> Do not use this method. (staticcheck)
Before this change, the step correlation code returned early in several cases:
- did not set f.planning.done in the cases where it was a no-op
- did not set f.planning.err in the cases where correlation did not
succeed
Reported-by: InsanePrawn <insane.prawny@gmail.com>
package trace:
- introduce the concept of tasks and spans, tracked as linked list within ctx
- see package-level docs for an overview of the concepts
- **main feature 1**: unique stack of task and span IDs
- makes it easy to follow a series of log entries in concurrent code
- **main feature 2**: ability to produce a chrome://tracing-compatible trace file
- either via an env variable or a `zrepl pprof` subcommand
- this is not a CPU profile, we already have go pprof for that
- but it is very useful to visually inspect where the
replication / snapshotter / pruner spends its time
( fixes#307 )
usage in package daemon/logging:
- goal: every log entry should have a trace field with the ID stack from package trace
- make `logging.GetLogger(ctx, Subsys)` the authoritative `logger.Logger` factory function
- the context carries a linked list of injected fields which
`logging.GetLogger` adds to the logger it returns
- `logging.GetLogger` also uses package `trace` to get the
task-and-span-stack and injects it into the returned logger's fields
Christian Schwarz