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logical size calculation: make .current_size() infallible (#5999)

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... by panicking on overflow;

It was made fallible initially due to in-confidence in logical size
calculation. However, the error has never happened since I am at Neon.

Let's stop worrying about this by converting the overflow check into a panic.
This commit is contained in:
Christian Schwarz
2023-11-29 15:34:46 +00:00
parent 1c88824ed0
commit 8cd28e1718
2 changed files with 7 additions and 9 deletions
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8
pageserver/src/tenant/timeline.rs
View File

@@ -859,7 +859,7 @@ impl Timeline {
self: &Arc<Self>,
ctx: &RequestContext,
) -> anyhow::Result<(u64, bool)> {
let current_size = self.current_logical_size.current_size()?;
let current_size = self.current_logical_size.current_size();
debug!("Current size: {current_size:?}");
let mut is_exact = true;
@@ -2057,16 +2057,14 @@ impl Timeline {
// one value while current_logical_size is set to the
// other.
match logical_size.current_size() {
Ok(CurrentLogicalSize::Exact(new_current_size)) => self
CurrentLogicalSize::Exact(new_current_size) => self
.metrics
.current_logical_size_gauge
.set(new_current_size),
Ok(CurrentLogicalSize::Approximate(_)) => {
CurrentLogicalSize::Approximate(_) => {
// don't update the gauge yet, this allows us not to update the gauge back and
// forth between the initial size calculation task.
}
// this is overflow
Err(e) => error!("Failed to compute current logical size for metrics update: {e:?}"),
}
}

8
pageserver/src/tenant/timeline/logical_size.rs
View File

@@ -102,23 +102,23 @@ impl LogicalSize {
}
}
pub(super) fn current_size(&self) -> anyhow::Result<CurrentLogicalSize> {
pub(super) fn current_size(&self) -> CurrentLogicalSize {
let size_increment: i64 = self.size_added_after_initial.load(AtomicOrdering::Acquire);
// ^^^ keep this type explicit so that the casts in this function break if
// we change the type.
match self.initial_logical_size.get() {
Some((initial_size, _)) => {
crate::metrics::initial_logical_size::CALLS.exact.inc();
initial_size.checked_add_signed(size_increment)
CurrentLogicalSize::Exact(initial_size.checked_add_signed(size_increment)
.with_context(|| format!("Overflow during logical size calculation, initial_size: {initial_size}, size_increment: {size_increment}"))
.map(CurrentLogicalSize::Exact)
.unwrap())
}
None => {
crate::metrics::initial_logical_size::CALLS
.approximate
.inc();
let non_negative_size_increment = u64::try_from(size_increment).unwrap_or(0);
Ok(CurrentLogicalSize::Approximate(non_negative_size_increment))
CurrentLogicalSize::Approximate(non_negative_size_increment)
}
}
}