only downsize underlying arrays if they're much too large

database/common.go

@@ -0,0 +1,14 @@
+package database
+
+const (
+	// MaxExcessCapacityFactor ...
+	// If, when a batch is reset, the cap(batch)/len(batch) > MaxExcessCapacityFactor,
+	// the underlying array's capacity will be reduced by a factor of capacityReductionFactor.
+	// Higher value for MaxExcessCapacityFactor --> less aggressive array downsizing --> less memory allocations
+	// but more unnecessary data in the underlying array that can't be garbage collected.
+	// Higher value for CapacityReductionFactor --> more aggressive array downsizing --> more memory allocations
+	// but less unnecessary data in the underlying array that can't be garbage collected.
+	MaxExcessCapacityFactor = 4
+	// CapacityReductionFactor ...
+	CapacityReductionFactor = 2
+)

database/encdb/db.go

@@ -17,10 +17,6 @@ import (
 	"github.com/ava-labs/gecko/utils/hashing"
 )
 
-const (
-	minBatchSize = 32
-)
-
 // Database encrypts all values that are provided
 type Database struct {
 	lock   sync.RWMutex
@@ -205,7 +201,11 @@ func (b *batch) Write() error {
 
 // Reset resets the batch for reuse.
 func (b *batch) Reset() {
-	b.writes = make([]keyValue, 0, minBatchSize)
+	if cap(b.writes) > len(b.writes)*database.MaxExcessCapacityFactor {
+		b.writes = make([]keyValue, 0, cap(b.writes)/database.CapacityReductionFactor)
+	} else {
+		b.writes = b.writes[:0]
+	}
 	b.Batch.Reset()
 }
 

database/memdb/db.go

@@ -15,8 +15,7 @@ import (
 
 const (
 	// DefaultSize is the default initial size of the memory database
-	DefaultSize  = 1 << 10
-	minBatchSize = 32
+	DefaultSize = 1 << 10
 )
 
 // Database is an ephemeral key-value store that implements the Database
@@ -194,7 +193,11 @@ func (b *batch) Write() error {
 
 // Reset implements the Batch interface
 func (b *batch) Reset() {
-	b.writes = make([]keyValue, 0, minBatchSize)
+	if cap(b.writes) > len(b.writes)*database.MaxExcessCapacityFactor {
+		b.writes = make([]keyValue, 0, cap(b.writes)/database.CapacityReductionFactor)
+	} else {
+		b.writes = b.writes[:0]
+	}
 	b.size = 0
 }
 

database/prefixdb/db.go

@@ -12,10 +12,6 @@ import (
 	"github.com/ava-labs/gecko/utils/hashing"
 )
 
-const (
-	minBatchSize = 32
-)
-
 // Database partitions a database into a sub-database by prefixing all keys with
 // a unique value.
 type Database struct {
@@ -203,7 +199,11 @@ func (b *batch) Write() error {
 
 // Reset resets the batch for reuse.
 func (b *batch) Reset() {
-	b.writes = make([]keyValue, 0, minBatchSize)
+	if cap(b.writes) > len(b.writes)*database.MaxExcessCapacityFactor {
+		b.writes = make([]keyValue, 0, cap(b.writes)/database.CapacityReductionFactor)
+	} else {
+		b.writes = b.writes[:0]
+	}
 	b.Batch.Reset()
 }
 

database/rpcdb/db_client.go

@@ -14,10 +14,6 @@ import (
 	"github.com/ava-labs/gecko/utils"
 )
 
-const (
-	minBatchSize = 32
-)
-
 var (
 	errClosed   = fmt.Sprintf("rpc error: code = Unknown desc = %s", database.ErrClosed)
 	errNotFound = fmt.Sprintf("rpc error: code = Unknown desc = %s", database.ErrNotFound)
@@ -184,7 +180,11 @@ func (b *batch) Write() error {
 }
 
 func (b *batch) Reset() {
-	b.writes = make([]keyValue, 0, minBatchSize)
+	if cap(b.writes) > len(b.writes)*database.MaxExcessCapacityFactor {
+		b.writes = make([]keyValue, 0, cap(b.writes)/database.CapacityReductionFactor)
+	} else {
+		b.writes = b.writes[:0]
+	}
 	b.size = 0
 }
 

database/versiondb/db.go

@@ -305,7 +305,11 @@ func (b *batch) Write() error {
 
 // Reset implements the Database interface
 func (b *batch) Reset() {
-	b.writes = make([]keyValue, 0)
+	if cap(b.writes) > len(b.writes)*database.MaxExcessCapacityFactor {
+		b.writes = make([]keyValue, 0, cap(b.writes)/database.CapacityReductionFactor)
+	} else {
+		b.writes = b.writes[:0]
+	}
 	b.size = 0
 }
 

ids/short_set.go

@@ -58,10 +58,10 @@ func (ids *ShortSet) Remove(idList ...ShortID) {
 func (ids *ShortSet) Clear() { *ids = nil }
 
 // CappedList returns a list of length at most [size].
-// Size should be >= 0. If size < 0, returns empty list.
+// Size should be >= 0. If size < 0, returns nil.
 func (ids ShortSet) CappedList(size int) []ShortID {
 	if size < 0 {
-		return make([]ShortID, 0, 0)
+		return nil
 	}
 	if l := ids.Len(); l < size {
 		size = l

snow/validators/set.go

@@ -13,6 +13,19 @@ import (
 	"github.com/ava-labs/gecko/utils/random"
 )
 
+const (
+	// maxExcessCapacityFactor ...
+	// If, when the validator set is reset, cap(set)/len(set) > MaxExcessCapacityFactor,
+	// the underlying arrays' capacities will be reduced by a factor of capacityReductionFactor.
+	// Higher value for maxExcessCapacityFactor --> less aggressive array downsizing --> less memory allocations
+	// but more unnecessary data in the underlying array that can't be garbage collected.
+	// Higher value for capacityReductionFactor --> more aggressive array downsizing --> more memory allocations
+	// but less unnecessary data in the underlying array that can't be garbage collected.
+	maxExcessCapacityFactor = 4
+	// CapacityReductionFactor ...
+	capacityReductionFactor = 2
+)
+
 // Set of validators that can be sampled
 type Set interface {
 	fmt.Stringer
@@ -72,9 +85,27 @@ func (s *set) Set(vdrs []Validator) {
 
 func (s *set) set(vdrs []Validator) {
 	lenVdrs := len(vdrs)
+	// If the underlying arrays are much larger than necessary, resize them to
+	// allow garbage collection of unused memory
+	if cap(s.vdrSlice) > len(s.vdrSlice)*maxExcessCapacityFactor {
+		newCap := cap(s.vdrSlice) / capacityReductionFactor
+		if newCap < lenVdrs {
+			newCap = lenVdrs
+		}
+		s.vdrSlice = make([]Validator, 0, newCap)
+	} else {
+		s.vdrSlice = s.vdrSlice[:0]
+	}
+	if cap(s.sampler.Weights) > len(s.sampler.Weights)*maxExcessCapacityFactor {
+		newCap := cap(s.sampler.Weights) / capacityReductionFactor
+		if newCap < lenVdrs {
+			newCap = lenVdrs
+		}
+		s.sampler.Weights = make([]uint64, 0, newCap)
+	} else {
+		s.sampler.Weights = s.sampler.Weights[:0]
+	}
 	s.vdrMap = make(map[[20]byte]int, lenVdrs)
-	s.vdrSlice = make([]Validator, 0, lenVdrs)
-	s.sampler.Weights = make([]uint64, 0, lenVdrs)
 
 	for _, vdr := range vdrs {
 		s.add(vdr)

vms/platformvm/vm.go

@@ -808,7 +808,7 @@ func (vm *VM) getValidators(validatorEvents *EventHeap) []validators.Validator {
 		validator.Wght = weight
 	}
 
-	vdrList := make([]validators.Validator, len(vdrMap), len(vdrMap))
+	vdrList := make([]validators.Validator, len(vdrMap))
 	i := 0
 	for _, validator := range vdrMap {
 		vdrList[i] = validator