Fix cache metrics

[rdettai-sk]

Description

Go through the cache metrics to make sure they are correct.

I didn't find any hit rate miss-calculation yet.

How was this PR tested?

Describe how you tested this PR.

[Copilot]

Pull request overview

This PR adjusts in-memory cache implementations to avoid treating re-inserting an already-cached key as an eviction, and adds a regression test to validate the corrected metrics behavior across cache policies.

Changes:

• Prevent put from evicting/replacing an existing entry when the key is already present (Lru, S3Fifo, TinyLfu).
• Add a test ensuring re-putting the same key does not increment eviction metrics and does not inflate the in-cache count.

Suppressed comments (2)

quickwit/quickwit-storage/src/cache/base_cache.rs:339

• contains_key short-circuits re-puts without updating the cache policy's internal access state. If duplicate puts happen due to concurrent miss races, the entry won't have its recency refreshed, which can lead to premature eviction. Using get here aligns better with the "immutable payload" pattern used in DiskSizedCache::put (which refreshes recency on already-cached keys).

        if self.cache.contains_key(&key) {
            return;
        }

quickwit/quickwit-storage/src/cache/base_cache.rs:467

• As with the other policies, short-circuiting on contains_key makes re-puts a pure no-op and does not refresh TinyLFU's internal access/frequency state. If re-puts happen due to concurrent miss races, this can undercount how "hot" the entry is and lead to earlier eviction than intended; using get would refresh policy state without changing your metrics counters.

        if self.cache.contains_key(&key) {
            return;
        }

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[Copilot]

🟡 Changes recommended

File-descriptor eviction accounting still incorrectly counts duplicate inserts and unsuccessful removals.

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Review details

• Files reviewed: 3/3 changed files
• Comments generated: 1
• Review effort level: Balanced