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Change MetricFamily dictionary key from 32 to 64 bits hash to reduce collisions #342

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Merged
merged 1 commit into from
Mar 19, 2025
Merged

Change MetricFamily dictionary key from 32 to 64 bits hash to reduce collisions #342

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12 changes: 6 additions & 6 deletions src/Prometheus.Client/LabelsHelper.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -61,19 +61,19 @@ int GetTupleSize(Type tupleType)
#endif
}

public static int GetHashCode<TTuple>(TTuple values)
public static int GetHashCode<TTuple>(TTuple values, int seed = 0)
#if NET6_0_OR_GREATER
where TTuple : struct, ITuple, IEquatable<TTuple>
#else
where TTuple : struct, IEquatable<TTuple>
#endif
{
return TupleHelper<TTuple>.GetTupleHashCode(values);
return TupleHelper<TTuple>.GetTupleHashCode(values, seed);
}

public static int GetHashCode(IReadOnlyList<string> values)
public static int GetHashCode(IReadOnlyList<string> values, int seed = 0)
{
var result = 0;
var result = seed;

// ReSharper disable once ForCanBeConvertedToForeach
// do not use for-each here, it allocates which is easy to avoid by for loop
Expand Down Expand Up @@ -260,9 +260,9 @@ public static string[] ToArray(TTuple values)
});
}

public static int GetTupleHashCode(TTuple values)
public static int GetTupleHashCode(TTuple values, int seed)
{
return _hashCodeReducer(values, 0, (item, _, aggregated) =>
return _hashCodeReducer(values, seed, (item, _, aggregated) =>
{
if (item == null)
throw new ArgumentException("Label value cannot be empty");
Expand Down
40 changes: 34 additions & 6 deletions src/Prometheus.Client/MetricFamily.cs
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Expand Up @@ -24,7 +24,7 @@ public sealed class MetricFamily<TMetric, TImplementation, TLabels, TConfig> : I
private readonly IReadOnlyList<string> _metricNames;
private readonly Func<TConfig, IReadOnlyList<string>, TImplementation> _instanceFactory;
private readonly Lazy<TImplementation> _unlabelled;
private readonly ConcurrentDictionary<int, TImplementation> _labelledMetrics;
private readonly ConcurrentDictionary<MetricKey, TImplementation> _labelledMetrics;

public MetricFamily(TConfig configuration, MetricType metricType, Func<TConfig, IReadOnlyList<string>, TImplementation> instanceFactory)
{
Expand All @@ -35,7 +35,7 @@ public MetricFamily(TConfig configuration, MetricType metricType, Func<TConfig,
_unlabelled = new Lazy<TImplementation>(() => _instanceFactory(_configuration, default));
LabelNames = LabelsHelper.FromArray<TLabels>(configuration.LabelNames);
if (configuration.LabelNames.Count > 0)
_labelledMetrics = new ConcurrentDictionary<int, TImplementation>();
_labelledMetrics = new ConcurrentDictionary<MetricKey, TImplementation>();
}

public string Name => _configuration.Name;
Expand Down Expand Up @@ -64,7 +64,7 @@ TMetric IMetricFamily<TMetric>.WithLabels(params string[] labels)
if (labels.Length != _configuration.LabelNames.Count)
throw new ArgumentException("Wrong number of labels");

var key = LabelsHelper.GetHashCode(labels);
var key = new MetricKey(labels);

if (_labelledMetrics.TryGetValue(key, out var metric))
{
Expand All @@ -83,7 +83,7 @@ TMetric IMetricFamily<TMetric>.RemoveLabelled(params string[] labels)
if (labels.Length != _configuration.LabelNames.Count)
throw new ArgumentException("Wrong number of labels");

var key = LabelsHelper.GetHashCode(labels);
var key = new MetricKey(labels);
_labelledMetrics.TryRemove(key, out var removed);

return removed;
Expand All @@ -94,7 +94,7 @@ public TMetric WithLabels(TLabels labels)
if (_labelledMetrics == null)
throw new InvalidOperationException("Metric family does not have any labels");

var key = LabelsHelper.GetHashCode(labels);
var key = new MetricKey(labels);

if (_labelledMetrics.TryGetValue(key, out var metric))
{
Expand All @@ -110,7 +110,7 @@ public TMetric RemoveLabelled(TLabels labels)
if (_labelledMetrics == null)
throw new InvalidOperationException("Metric family does not have any labels");

var key = LabelsHelper.GetHashCode(labels);
var key = new MetricKey(labels);
_labelledMetrics.TryRemove(key, out var removed);

return removed;
Expand Down Expand Up @@ -148,4 +148,32 @@ private IEnumerable<KeyValuePair<IReadOnlyList<string>, TMetric>> EnumerateLabel
foreach (var labelled in _labelledMetrics)
yield return new KeyValuePair<IReadOnlyList<string>, TMetric>(labelled.Value.LabelValues, labelled.Value);
}

private readonly struct MetricKey : IEquatable<MetricKey>
{
private readonly int _hash1;
private readonly int _hash2;

public MetricKey(TLabels labels)
{
_hash1 = LabelsHelper.GetHashCode(labels, 0);
_hash2 = LabelsHelper.GetHashCode(labels, 42);
}

public MetricKey(params string[] labels)
{
_hash1 = LabelsHelper.GetHashCode(labels, 0);
_hash2 = LabelsHelper.GetHashCode(labels, 42);
}

public override int GetHashCode()
{
return _hash1;
}

public bool Equals(MetricKey other)
{
return _hash1 == other._hash1 && _hash2 == other._hash2;
}
}
}