transitory/dist/esm/cache/metrics/MetricsCache.js

In-memory cache with high hit rates via LFU eviction. Supports time-based expiration, automatic loading and metrics.

import { WrappedCache } from '../WrappedCache';
const METRICS = Symbol('metrics');
/**
 * Extension to a cache that tracks metrics about the size and hit rate of
 * a cache.
 */
export class MetricsCache extends WrappedCache {
    constructor(options) {
        super(options.parent, options.removalListener || null);
        this[METRICS] = {
            hits: 0,
            misses: 0,
            get hitRate() {
                const total = this.hits + this.misses;
                if (total === 0)
                    return 1.0;
                return this.hits / total;
            }
        };
    }
    /**
     * Get metrics for this cache. Returns an object with the keys `hits`,
     * `misses` and `hitRate`. For caches that do not have metrics enabled
     * trying to access metrics will throw an error.
     *
     * @returns
     *   metrics of cache
     */
    get metrics() {
        return this[METRICS];
    }
    /**
     * Get the cached value for the specified key if it exists. Will return
     * the value or `null` if no cached value exist. Updates the usage of the
     * key.
     *
     * @param key -
     *   key to get
     * @returns
     *   current value or `null`
     */
    getIfPresent(key) {
        const result = super.getIfPresent(key);
        if (result === null) {
            this[METRICS].misses++;
        }
        else {
            this[METRICS].hits++;
        }
        return result;
    }
}
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