Limit the number of buckets in verifiedTransactionCache to 3. (#2775)

The number of buckets in verifiedTransactionCache can be arbitrarily large depending on the requested cache size, and each lookup in the cache does that many map lookups. This PR limits the number of buckets to 3. Now, the lookup takes at most 3 lookups and the size overhead is 1.5.

Author: tolikzinovyev

data/transactions/verify/verifiedTxnCache.go

@@ -26,7 +26,6 @@ import (
 	"github.com/algorand/go-algorand/protocol"
 )
 
-const entriesPerBucket = 8179 // the default bucket size; a prime number could promote a lower hash collisions in case the hash function isn't perfect.
 const maxPinnedEntries = 500000
 
 // VerifiedTxnCacheError helps to identify the errors of a cache error and diffrenciate these from a general verification errors.
@@ -72,6 +71,8 @@ type VerifiedTransactionCache interface {
 
 // verifiedTransactionCache provides an implementation of the VerifiedTransactionCache interface
 type verifiedTransactionCache struct {
+	// Number of entries in each map (bucket).
+	entriesPerBucket int
 	// bucketsLock is the lock for syncornizing the access to the cache
 	bucketsLock deadlock.Mutex
 	// buckets is the circular cache buckets buffer
@@ -84,14 +85,14 @@ type verifiedTransactionCache struct {
 
 // MakeVerifiedTransactionCache creates an instance of verifiedTransactionCache and returns it.
 func MakeVerifiedTransactionCache(cacheSize int) VerifiedTransactionCache {
-	bucketsCount := 1 + (cacheSize / entriesPerBucket)
 	impl := &verifiedTransactionCache{
-		buckets: make([]map[transactions.Txid]*GroupContext, bucketsCount),
-		pinned:  make(map[transactions.Txid]*GroupContext, cacheSize),
-		base:    0,
+		entriesPerBucket: (cacheSize + 1) / 2,
+		buckets:          make([]map[transactions.Txid]*GroupContext, 3),
+		pinned:           make(map[transactions.Txid]*GroupContext, cacheSize),
+		base:             0,
 	}
-	for i := 0; i < bucketsCount; i++ {
-		impl.buckets[i] = make(map[transactions.Txid]*GroupContext, entriesPerBucket)
+	for i := 0; i < len(impl.buckets); i++ {
+		impl.buckets[i] = make(map[transactions.Txid]*GroupContext, impl.entriesPerBucket)
 	}
 	return impl
 }
@@ -245,10 +246,10 @@ func (v *verifiedTransactionCache) Pin(txgroup []transactions.SignedTxn) (err er
 
 // add is the internal implementation of Add/AddPayset which adds a transaction group to the buffer.
 func (v *verifiedTransactionCache) add(txgroup []transactions.SignedTxn, groupCtx *GroupContext) {
-	if len(v.buckets[v.base])+len(txgroup) > entriesPerBucket {
+	if len(v.buckets[v.base])+len(txgroup) > v.entriesPerBucket {
 		// move to the next bucket while deleting the content of the next bucket.
 		v.base = (v.base + 1) % len(v.buckets)
-		v.buckets[v.base] = make(map[transactions.Txid]*GroupContext, entriesPerBucket)
+		v.buckets[v.base] = make(map[transactions.Txid]*GroupContext, v.entriesPerBucket)
 	}
 	currentBucket := v.buckets[v.base]
 	for _, txn := range txgroup {

data/transactions/verify/verifiedTxnCache_test.go

@@ -49,7 +49,8 @@ func TestBucketCycling(t *testing.T) {
 	partitiontest.PartitionTest(t)
 
 	bucketCount := 3
-	icache := MakeVerifiedTransactionCache(entriesPerBucket * bucketCount)
+	entriesPerBucket := 100
+	icache := MakeVerifiedTransactionCache(entriesPerBucket * (bucketCount - 1))
 	impl := icache.(*verifiedTransactionCache)
 	_, signedTxn, _, _ := generateTestObjects(entriesPerBucket*bucketCount*2, bucketCount, 0)
 
@@ -58,7 +59,7 @@ func TestBucketCycling(t *testing.T) {
 	require.NoError(t, err)
 
 	// fill up the cache with entries.
-	for i := 0; i < entriesPerBucket*(bucketCount+1); i++ {
+	for i := 0; i < entriesPerBucket*bucketCount; i++ {
 		impl.Add([]transactions.SignedTxn{signedTxn[i]}, groupCtx)
 		// test to see that the base is sliding when bucket get filled up.
 		require.Equal(t, i/entriesPerBucket, impl.base)
@@ -136,13 +137,13 @@ func BenchmarkGetUnverifiedTranscationGroups50(b *testing.B) {
 func TestUpdatePinned(t *testing.T) {
 	partitiontest.PartitionTest(t)
 
-	size := entriesPerBucket
+	size := 100
 	icache := MakeVerifiedTransactionCache(size * 10)
 	impl := icache.(*verifiedTransactionCache)
 	_, signedTxn, secrets, addrs := generateTestObjects(size*2, 10, 0)
 	txnGroups := generateTransactionGroups(signedTxn, secrets, addrs)
 
-	// insert half of the entries.
+	// insert some entries.
 	for i := 0; i < len(txnGroups); i++ {
 		groupCtx, _ := PrepareGroupContext(txnGroups[i], blockHeader)
 		impl.Add(txnGroups[i], groupCtx)
@@ -165,7 +166,7 @@ func TestUpdatePinned(t *testing.T) {
 func TestPinningTransactions(t *testing.T) {
 	partitiontest.PartitionTest(t)
 
-	size := entriesPerBucket
+	size := 100
 	icache := MakeVerifiedTransactionCache(size)
 	impl := icache.(*verifiedTransactionCache)
 	_, signedTxn, secrets, addrs := generateTestObjects(size*2, 10, 0)
@@ -182,5 +183,4 @@ func TestPinningTransactions(t *testing.T) {
 
 	// try to pin an entry that was not added.
 	require.Error(t, impl.Pin(txnGroups[len(txnGroups)-1]))
-
 }