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package zip
import (
"time"
"github.com/karlseguin/ccache/v2"
"gitlab.com/gitlab-org/gitlab-pages/metrics"
)
// lruCacheGetPerPromote is a value that makes the item to be promoted
// it is taken arbitrally as a sane value indicating that the item
// was frequently picked
// promotion moves the item to the front of the LRU list
const lruCacheGetsPerPromote = 64
// lruCacheItemsToPruneDiv is a value that indicates how much items
// needs to be pruned on OOM, this prunes 1/16 of items
const lruCacheItemsToPruneDiv = 16
type lruCache struct {
op string
duration time.Duration
cache *ccache.Cache
}
func newLruCache(op string, maxEntries int64, duration time.Duration) *lruCache {
configuration := ccache.Configure()
configuration.MaxSize(maxEntries)
configuration.ItemsToPrune(uint32(maxEntries) / lruCacheItemsToPruneDiv)
configuration.GetsPerPromote(lruCacheGetsPerPromote) // if item gets requested frequently promote it
configuration.OnDelete(func(*ccache.Item) {
metrics.ZipCachedEntries.WithLabelValues(op).Dec()
})
return &lruCache{
op: op,
cache: ccache.New(configuration),
duration: duration,
}
}
func (c *lruCache) findOrFetch(cacheNamespace, key string, fetchFn func() (interface{}, error)) (interface{}, error) {
item := c.cache.Get(cacheNamespace + key)
if item != nil && !item.Expired() {
metrics.ZipCacheRequests.WithLabelValues(c.op, "hit").Inc()
return item.Value(), nil
}
value, err := fetchFn()
if err != nil {
metrics.ZipCacheRequests.WithLabelValues(c.op, "error").Inc()
return nil, err
}
metrics.ZipCacheRequests.WithLabelValues(c.op, "miss").Inc()
metrics.ZipCachedEntries.WithLabelValues(c.op).Inc()
c.cache.Set(cacheNamespace+key, value, c.duration)
return value, nil
}
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