e9eda7e7c8
* cache: add sharded cache implementation Add Cache impl and a few tests. This cache is 256-way sharded, mainly so each shard has it's own lock. The main cache structure is a readonly jump plane into the right shard. This should remove the single lock contention on the main lock and provide more concurrent throughput - Obviously this hasn't been tested or measured. The key into the cache was made a uint32 (hash.fnv) and the hashing op is not using strings.ToLower anymore remove any GC in that code path. * here too * Minimum shard size * typos * blurp * small cleanups no defer * typo * Add freq based on Johns idea * cherry-pick conflict resolv * typo * update from early code review from john * add prefetch to the cache * mw/cache: add prefetch * remove println * remove comment * Fix tests * Test prefetch in setup * Add start of cache * try add diff cache options * Add hacky testcase * not needed * allow the use of a percentage for prefetch If the TTL falls below xx% do a prefetch, if the record was popular. Some other fixes and correctly prefetch only popular records. |
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|---|---|---|
| .. | ||
| freq | ||
| cache.go | ||
| cache_test.go | ||
| handler.go | ||
| item.go | ||
| prefech_test.go | ||
| README.md | ||
| setup.go | ||
| setup_test.go | ||
cache
cache enables a frontend cache. It will cache all records except zone transfers and metadata records.
Syntax
cache [TTL] [ZONES...]
- TTL max TTL in seconds. If not specified, the maximum TTL will be used which is 3600 for noerror responses and 1800 for denial of existence ones. Setting a TTL of 300 cache 300 would cache the record up to 300 seconds.
- ZONES zones it should cache for. If empty, the zones from the configuration block are used.
Each element in the cache is cached according to its TTL (with TTL as the max). For the negative cache, the SOA's MinTTL value is used. A cache can contain up to 10,000 items by default. A TTL of zero is not allowed.
If you want more control:
cache [TTL] [ZONES...] {
success CAPACITY [TTL]
denial CAPACITY [TTL]
prefetch AMOUNT [[DURATION] [PERCENTAGE%]]
}
- TTL and ZONES as above.
success, override the settings for caching successful responses, CAPACITY indicates the maximum number of packets we cache before we start evicting (randomly). TTL overrides the cache maximum TTL.denial, override the settings for caching denial of existence responses, CAPACITY indicates the maximum number of packets we cache before we start evicting (LRU). TTL overrides the cache maximum TTL. There is a third category (error) but those responses are never cached.prefetch, will prefetch popular items when they are about to be expunged from the cache. Popular means AMOUNT queries have been seen no gaps of DURATION or more between them. DURATION defaults to 1m. Prefetching will happen when the TTL drops below PERCENTAGE, which defaults to10%. Values should be in the range[10%, 90%]. Note the percent sign is mandatory. PERCENTAGE is treated as anint.
The minimum TTL allowed on resource records is 5 seconds.
Metrics
If monitoring is enabled (via the prometheus directive) then the following metrics are exported:
- coredns_cache_size{type} - Total elements in the cache by cache type.
- coredns_cache_capacity{type} - Total capacity of the cache by cache type.
- coredns_cache_hits_total{type} - Counter of cache hits by cache type.
- coredns_cache_misses_total - Counter of cache misses.
Cache types are either "denial" or "success".
Examples
Enable caching for all zones, but cap everything to a TTL of 10 seconds:
cache 10
Proxy to Google Public DNS and only cache responses for example.org (or below).
proxy . 8.8.8.8:53
cache example.org