fix(conflict): Charge the signature cache by target capacity

Author: manjari25

submitqueue/extension/conflict/tango/cache.go

@@ -20,7 +20,8 @@ import (
 )
 
 // The budget counts memory: a SignatureTarget is 16 bytes (uint64 plus int32,
-// padded), and the fixed overhead covers the entry, key and map bookkeeping.
+// padded) and the backing array is charged by capacity, and the fixed overhead
+// covers the entry, key and map bookkeeping.
 const (
 	signatureTargetBytes   = 16
 	signatureEntryOverhead = 256
@@ -59,7 +60,7 @@ func newSignatureCache(maxBytes int64) *signatureCache {
 func signatureCacheBytes(signature TargetSignature) int64 {
 	return signatureEntryOverhead +
 		int64(len(signature.Queue)+len(signature.BatchID)+len(signature.BaseRevision)) +
-		int64(len(signature.Targets))*signatureTargetBytes
+		int64(cap(signature.Targets))*signatureTargetBytes
 }
 
 // get returns the cached signature and marks it most recently used.

submitqueue/extension/conflict/tango/cache_test.go

@@ -102,15 +102,15 @@ func TestSignatureCache_Eviction(t *testing.T) {
 					cache.put(a)
 				}
 			},
-			wantFound: map[string]bool{"a": true, "b": true, "c": false},
+			wantFound: map[string]bool{"a": true, "b": true},
 		},
 		{
 			name: "a signature larger than the budget is not cached",
 			run: func(cache *signatureCache) {
 				cache.put(a)
 				cache.put(cacheTestSignature("q", "c", 1000))
 			},
-			wantFound: map[string]bool{"a": true, "b": false, "c": false},
+			wantFound: map[string]bool{"a": true, "c": false},
 		},
 	}
 	for _, tt := range tests {
@@ -127,6 +127,18 @@ func TestSignatureCache_Eviction(t *testing.T) {
 	}
 }
 
+func TestSignatureCache_ChargesSpareCapacity(t *testing.T) {
+	tight := cacheTestSignature("q", "tight", 10)
+	roomy := cacheTestSignature("q", "roomy", 10)
+	roomy.Targets = append(make([]SignatureTarget, 0, 1000), roomy.Targets...)
+	cache := newSignatureCache(signatureCacheBytes(tight) * 2)
+
+	cache.put(roomy)
+
+	_, found := cache.get("q", "roomy")
+	assert.False(t, found)
+}
+
 func TestSignatureCache_ZeroBudgetCachesNothing(t *testing.T) {
 	cache := newSignatureCache(0)