Diskcache: querier-local SSD backed chunk cache #685
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- Caches don't know about chunk anymore, its all just []byte. - Deal with empty memcached host by returning a noopCache, not special casing nil client. - Make background writes a cache 'middleware'. - s/memcache/memcached/. - Refactor tests.
- mmap a large file, treat it as a series of 2KB buckets. - Use FNV hash to place key and chunk in buckets. - Use existing memcached tests
tomwilkie
changed the title
|
We've had this running for about a week without problems. Performance impact is hard to measure, we see the diskcache taking about 0.5ms vs 33ms memcache (99th percentile fetch), but a relatively low hit rate of 70% vs memcache which is always at 100%. Given that this is disabled by default, I think the PR is worth it just for the refactoring. |
bboreham
approved these changes
Feb 20, 2018
pkg/chunk/chunk_store.go
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| // ProcessCacheResponse decodes the chunks coming back from the cache, separating | ||
| // hits and misses. | ||
| func ProcessCacheResponse(chunks []Chunk, keys []string, bufs [][]byte) (found []Chunk, missing []Chunk, err error) { | ||
| ctx := NewDecodeContext() |
There was a problem hiding this comment.
ctx jars - I would expect that to be a context.Context
pkg/chunk/chunk_store.go
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| cacheCorrupt = prometheus.NewCounter(prometheus.CounterOpts{ | ||
| Namespace: "cortex", | ||
| Name: "cache_corrupt_chunks_total", | ||
| Help: "Total count of corrupt chunks found in memcache.", |
pkg/chunk/cache/instrumented.go
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| fetchedKeys = prometheus.NewCounterVec(prometheus.CounterOpts{ | ||
| Namespace: "cortex", | ||
| Name: "cache_fetched_keys", | ||
| Help: "Total count of chunks requested from memcache.", |
pkg/chunk/cache/instrumented.go
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| hits = prometheus.NewCounterVec(prometheus.CounterOpts{ | ||
| Namespace: "cortex", | ||
| Name: "cache_hits", | ||
| Help: "Total count of chunks found in memcache.", |
|
Thanks @bboreham |
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An on-disk cache, for caching chunks on local SSD in queriers. Uses a large mmap'd file, treated as a series of 2KB buckets, uses FNV hash to place key and chunk in buckets.
Also a bunch of refactoring of the memcache module, see commits.
Still a work in progress, will update with results.