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[ENH] Write to disk on eviction instead of insertion #5974

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[ENH] Write to disk on eviction instead of insertion #5974

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2 changes: 1 addition & 1 deletion rust/cache/src/foyer.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -349,7 +349,7 @@ where
.with_name(config.name.clone())
.with_metrics_registry(otel_0_27_metrics)
.with_tracing_options(tracing_options.clone())
.with_policy(foyer::HybridCachePolicy::WriteOnInsertion)
.with_policy(foyer::HybridCachePolicy::WriteOnEviction)
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[Documentation] This change from WriteOnInsertion to WriteOnEviction is a good optimization for insert latency, as it defers disk writes until an item is evicted from the in-memory tier.

This introduces a trade-off: improved performance at the cost of durability. In the case of an unclean shutdown (e.g., a process crash), any data in the memory cache that hasn't been evicted will be lost. The previous WriteOnInsertion policy provided stronger durability against crashes.

This is a reasonable trade-off for a cache, but it's an important change in behavior. To ensure this is clear for future maintainers, could you add a brief note about this durability trade-off to the PR description?

Context for Agents 
This change from `WriteOnInsertion` to `WriteOnEviction` is a good optimization for insert latency, as it defers disk writes until an item is evicted from the in-memory tier.

This introduces a trade-off: improved performance at the cost of durability. In the case of an unclean shutdown (e.g., a process crash), any data in the memory cache that hasn't been evicted will be lost. The previous `WriteOnInsertion` policy provided stronger durability against crashes.

This is a reasonable trade-off for a cache, but it's an important change in behavior. To ensure this is clear for future maintainers, could you add a brief note about this durability trade-off to the PR description?

File: rust/cache/src/foyer.rs
Line: 352

.memory(config.mem)
.with_shards(config.shards);

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