apache/dubbo · error · IllegalArgumentException

Illegal eviction factor value:${evictionFactor}

Error message

Illegal eviction factor value:${evictionFactor}

What it means

LFUCache constructor validates that evictionFactor is in the exclusive-open range (0, 1] and not NaN. Out-of-range or NaN factors are rejected because they determine how many entries are evicted when capacity is exceeded.

Source

Thrown at dubbo-common/src/main/java/org/apache/dubbo/common/utils/LFUCache.java:56

        this(DEFAULT_INITIAL_CAPACITY, DEFAULT_EVICTION_FACTOR);
    }

    /**
     * Constructs and initializes cache with specified capacity and eviction
     * factor. Unacceptable parameter values followed with
     * {@link IllegalArgumentException}.
     *
     * @param maxCapacity    cache max capacity
     * @param evictionFactor cache proceedEviction factor
     */
    @SuppressWarnings("unchecked")
    public LFUCache(final int maxCapacity, final float evictionFactor) {
        if (maxCapacity <= 0) {
            throw new IllegalArgumentException("Illegal initial capacity: " + maxCapacity);
        }
        boolean factorInRange = evictionFactor <= 1 && evictionFactor > 0;
        if (!factorInRange || Float.isNaN(evictionFactor)) {
            throw new IllegalArgumentException("Illegal eviction factor value:" + evictionFactor);
        }
        this.capacity = maxCapacity;
        this.evictionCount = (int) (capacity * evictionFactor);
        this.map = new HashMap<>();
        this.freqTable = new CacheDeque[capacity + 1];
        for (int i = 0; i <= capacity; i++) {
            freqTable[i] = new CacheDeque<>();
        }
        for (int i = 0; i < capacity; i++) {
            freqTable[i].nextDeque = freqTable[i + 1];
        }
        freqTable[capacity].nextDeque = freqTable[capacity];
    }

    public int getCapacity() {
        return capacity;
    }

View on GitHub (pinned to 3a3043227f)

Solutions

1. Express the eviction factor as a fraction strictly greater than 0 and <= 1
2. Validate/clamp the config value at load time before constructing the cache
3. Default to a safe value like 0.8 when the property is missing

Example fix

// before
new LFUCache<>(100, 80f);   // 80 > 1, rejected
// after
new LFUCache<>(100, 0.8f);

float f = configuredFactor;
if (!(f > 0 && f <= 1) || Float.isNaN(f)) throw new IllegalArgumentException("bad factor: " + f);
new LFUCache<>(100, f);

static boolean validFactor(float f) { return !Float.isNaN(f) && f > 0 && f <= 1; }

try { new LFUCache<>(cap, factor); }
catch (IllegalArgumentException e) { /* factor out of (0,1]; default to 0.8f */ }

When it happens

Trigger: Instantiating new LFUCache(capacity, factor) where factor is <= 0, > 1, or Float.NaN; e.g. reading the factor from config without bounds checking.

Common situations: Eviction-factor config property mis-typed (e.g. 20 instead of 0.20); division producing 0 or NaN; copy-paste from a percentage (80) instead of a fraction (0.8).

Related errors

• Illegal initial capacity: ${maxCapacity}
• Invalid configurator rule, please specify at least one param
• service field in configuration is null.
• Illegal affinity rule!
• Illegal route rule!

AI-assisted analysis of apache/dubbo@3a3043227f (2026-08-14). Data as JSON: /api/errors/29760aeb0307879e. Report an issue: GitHub.