Change pooling options for index array pool to prevent (almost) unbou…

…nded growth over time (#1254)

src/m3ninx/index/segment/mem/options.go

@@ -32,6 +32,11 @@ import (
 const (
 	defaultInitialCapacity        = 1024
 	defaultBytesArrayPoolCapacity = 1024
+	// This pool is used in a single-threaded manner.
+	defaultBytesArrayPoolSize = 1
+	// 2^24 * 16 bytes (byte slice pointer) * 2 (Golang G.C) ~=
+	// 0.5 GiB max memory usage.
+	defaultBytesArrayPoolMaxArrayCapacity = 2 ^ 24
 )
 
 // Options is a collection of knobs for an in-memory segment.
@@ -78,8 +83,12 @@ type opts struct {
 // NewOptions returns new options.
 func NewOptions() Options {
 	arrPool := bytes.NewSliceArrayPool(bytes.SliceArrayPoolOpts{
-		Capacity: defaultBytesArrayPoolCapacity,
-		Options:  pool.NewObjectPoolOptions(),
+		Capacity:    defaultBytesArrayPoolCapacity,
+		MaxCapacity: defaultBytesArrayPoolMaxArrayCapacity,
+		Options: pool.NewObjectPoolOptions().
+			SetSize(defaultBytesArrayPoolSize).
+			SetRefillLowWatermark(0).
+			SetRefillHighWatermark(0),
 	})
 	arrPool.Init()
 	return &opts{