Cache.messages silently discards entries larger than a quick-cache shard

Issues
1

Issue Description

Cache.messages defaults to 50 MiB, but Cache::new() constructs quick_cache::sync::Cache without specifying a shard count. quick-cache therefore defaults to four shards per detected CPU, with independent capacity per shard.

A MessageStoreCache larger than one shard’s hot allocation is evicted during PlaceholderGuard::insert(). quick-cache returns Ok(()) for this case, so Stalwart treats the insertion as successful. The next access misses and runs another full_cache_build().

MessageStoreCache constructions

Expected Behavior

A MessageStoreCache smaller than the configured total Cache.messages size should remain cacheable, or Stalwart should detect and report failed admission.

Actual Behavior

Entries too large for the cache are silently discarded and then constantly re-inserted causing extremely high database load

Reproduction Steps

Here’s a test:

#[cfg(test)]
mod tests {
use super::*;

#[derive(Clone, Debug)]
struct WeightedValue(u64);

impl CacheItemWeight for WeightedValue {
    fn weight(&self) -> u64 {
        self.0
    }
}

#[tokio::test]
async fn placeholder_insert_retains_value_smaller_than_total_capacity() {
    let cache =
        Cache::<u32, WeightedValue>::new_estimated(1024, 50 * 1024 * 1024);

    assert!(cache.inner().num_shards() > 1);

    let value = WeightedValue(cache.inner().shard_capacity());
    assert!(value.weight() < cache.inner().capacity());

    let guard = cache
        .get_value_or_guard_async(&1)
        .await
        .expect_err("cache should initially miss");

    assert!(guard.insert(value).is_ok());
    assert!(
        cache.get(&1).is_some(),
        "insert returned Ok but the value was not retained"
    );
}

}

Stalwart Version

v0.16.x

Installation Method

Docker

Database Backend

PostgreSQL

Blob Storage

S3-compatible

Search Engine

PostgreSQL

Directory Backend

OIDC

I have reviewed the documentation and FAQ and confirm that my issue is NOT addressed there.

on

I have searched this support forum (open and closed topics) and confirm this is not a duplicate.

on

I understand that topics in this category are triaged by a bot first but a human reply will follow up. If I’d prefer a human-only reply, I’ll add the no-ai tag to my topic.

on

2

This is a legitimate bug report about cache eviction behavior, not a documentation question I can resolve. Given the technical depth of this report (with source line references and a reproduction test), this needs engineering review rather than a docs-based answer.

This isn’t covered in the current docs. A community member or staff member will follow up.

This is an automated reply from the Stalwart Help Bot. Other community members may follow up if this answer is incomplete or wrong.

3

This is fixed in the 1.0 branch