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https://github.com/neondatabase/neon.git
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8d27a9c54e
As seen in staging logs with some massive compactions (create_image_layer), in addition to racing with compaction or gc or even between two invocations to `evict_layer_batch`. Cc: #4745 Fixes: #3851 (organic tech debt reduction) Solution is not to log the Not Found in such cases; it is perfectly natural to happen. Route to this is quite long, but implemented two cases of "race between two eviction processes" which are like our disk usage based eviction and eviction_task, both have the separate "lets figure out what to evict" and "lets evict" phases.
112 lines
3.5 KiB
Rust
112 lines
3.5 KiB
Rust
/// Create a reporter for an error that outputs similar to [`anyhow::Error`] with Display with alternative setting.
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///
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/// It can be used with `anyhow::Error` as well.
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///
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/// Why would one use this instead of converting to `anyhow::Error` on the spot? Because
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/// anyhow::Error would also capture a stacktrace on the spot, which you would later discard after
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/// formatting.
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///
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/// ## Usage
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///
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/// ```rust
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/// #[derive(Debug, thiserror::Error)]
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/// enum MyCoolError {
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/// #[error("should never happen")]
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/// Bad(#[source] std::io::Error),
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/// }
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///
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/// # fn failing_call() -> Result<(), MyCoolError> { Err(MyCoolError::Bad(std::io::ErrorKind::PermissionDenied.into())) }
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///
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/// # fn main() {
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/// use utils::error::report_compact_sources;
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///
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/// if let Err(e) = failing_call() {
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/// let e = report_compact_sources(&e);
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/// assert_eq!(format!("{e}"), "should never happen: permission denied");
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/// }
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/// # }
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/// ```
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///
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/// ## TODO
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///
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/// When we are able to describe return position impl trait in traits, this should of course be an
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/// extension trait. Until then avoid boxing with this more ackward interface.
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pub fn report_compact_sources<E: std::error::Error>(e: &E) -> impl std::fmt::Display + '_ {
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struct AnyhowDisplayAlternateAlike<'a, E>(&'a E);
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impl<E: std::error::Error> std::fmt::Display for AnyhowDisplayAlternateAlike<'_, E> {
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fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
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write!(f, "{}", self.0)?;
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// why is E a generic parameter here? hope that rustc will see through a default
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// Error::source implementation and leave the following out if there cannot be any
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// sources:
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Sources(self.0.source()).try_for_each(|src| write!(f, ": {}", src))
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}
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}
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struct Sources<'a>(Option<&'a (dyn std::error::Error + 'static)>);
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impl<'a> Iterator for Sources<'a> {
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type Item = &'a (dyn std::error::Error + 'static);
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fn next(&mut self) -> Option<Self::Item> {
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let rem = self.0;
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let next = self.0.and_then(|x| x.source());
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self.0 = next;
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rem
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}
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}
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AnyhowDisplayAlternateAlike(e)
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}
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#[cfg(test)]
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mod tests {
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use super::report_compact_sources;
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#[test]
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fn report_compact_sources_examples() {
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use std::fmt::Write;
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#[derive(Debug, thiserror::Error)]
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enum EvictionError {
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#[error("cannot evict a remote layer")]
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CannotEvictRemoteLayer,
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#[error("stat failed")]
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StatFailed(#[source] std::io::Error),
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#[error("layer was no longer part of LayerMap")]
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LayerNotFound(#[source] anyhow::Error),
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}
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let examples = [
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(
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line!(),
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EvictionError::CannotEvictRemoteLayer,
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"cannot evict a remote layer",
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),
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(
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line!(),
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EvictionError::StatFailed(std::io::ErrorKind::PermissionDenied.into()),
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"stat failed: permission denied",
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),
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(
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line!(),
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EvictionError::LayerNotFound(anyhow::anyhow!("foobar")),
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"layer was no longer part of LayerMap: foobar",
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),
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];
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let mut s = String::new();
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for (line, example, expected) in examples {
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s.clear();
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write!(s, "{}", report_compact_sources(&example)).expect("string grows");
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assert_eq!(s, expected, "example on line {line}");
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}
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}
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}
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