Pre-allocate batchwise via mmap

internal/memstore/allocator.go

@@ -1,6 +1,8 @@
 package memstore
 
 import (
+	"errors"
+	"log"
 	"os"
 	"reflect"
 	"sync"
@@ -16,20 +18,26 @@ const bufferSizeInBytes int = bufferSizeInFloats * 8
 // The allocator rarely used, so a single big lock should be fine!
 var allocatorLock sync.Mutex
 var allocatorPool [][]byte
+var allocatorBatch []byte
 
 func RequestBytes(size int) []byte {
 	requested := size
 	size = (size + bufferSizeInBytes - 1) / bufferSizeInBytes * bufferSizeInBytes
-	if size == bufferSizeInBytes {
-		allocatorLock.Lock()
-		if len(allocatorPool) > 0 {
-			bytes := allocatorPool[len(allocatorPool)-1]
-			allocatorPool = allocatorPool[:len(allocatorPool)-1]
-			allocatorLock.Unlock()
-			return bytes
-		}
+
+	// Check allocation caches:
+	allocatorLock.Lock()
+	if len(allocatorPool) > 0 && size == bufferSizeInBytes {
+		bytes := allocatorPool[len(allocatorPool)-1]
+		allocatorPool = allocatorPool[:len(allocatorPool)-1]
 		allocatorLock.Unlock()
+		return bytes[:requested]
+	} else if cap(allocatorBatch) > size {
+		bytes := allocatorBatch[:0:size]
+		allocatorBatch = allocatorBatch[size:]
+		allocatorLock.Unlock()
+		return bytes[:requested]
 	}
+	allocatorLock.Unlock()
 
 	pagesize := os.Getpagesize()
 	if size < pagesize || size%pagesize != 0 {
@@ -48,6 +56,35 @@ func RequestBytes(size int) []byte {
 	return bytes[:requested]
 }
 
+func FillAllocatorCache(estimate int) error {
+	size := (estimate + bufferSizeInBytes - 1) / bufferSizeInBytes * bufferSizeInBytes
+	pagesize := os.Getpagesize()
+	if size < pagesize || size%pagesize != 0 {
+		return errors.New("estimate to small of buffer size not page size compatible")
+	}
+
+	allocatorLock.Lock()
+	defer allocatorLock.Unlock()
+
+	if len(allocatorBatch) > 0 {
+		n := len(allocatorBatch) / bufferSizeInBytes
+		for i := 0; i < n; i++ {
+			chunk := allocatorBatch[i*bufferSizeInBytes : i*bufferSizeInBytes+bufferSizeInBytes]
+			allocatorPool = append(allocatorPool, chunk[0:0:bufferSizeInBytes])
+		}
+		allocatorBatch = nil
+	}
+
+	bytes, err := unix.Mmap(-1, 0, size, unix.PROT_READ|unix.PROT_WRITE, unix.MAP_ANONYMOUS|unix.MAP_SHARED)
+	if err != nil {
+		panic("unix.Mmap failed: " + err.Error())
+	}
+
+	log.Printf("batch-allocated %d bytes", cap(bytes))
+	allocatorBatch = bytes
+	return nil
+}
+
 func ReleaseBytes(bytes []byte) {
 	if cap(bytes)%bufferSizeInBytes != 0 {
 		panic("bytes released that do not match the buffer size constraints")

internal/memstore/checkpoints.go

@@ -42,6 +42,7 @@ func (c *Checkpoint) Serialize(w io.Writer) error {
 	buf = encodeBytes(buf, c.Reserved)
 	buf = encodeUint64(buf, c.From)
 	buf = encodeUint64(buf, c.To)
+	buf = encodeUint64(buf, 0) // Estimate zero for non-streaming checkpoints
 
 	// The rest:
 	var err error
@@ -129,6 +130,9 @@ func (c *Checkpoint) Deserialize(r *bufio.Reader) error {
 	if c.To, err = decodeUint64(buf, r); err != nil {
 		return err
 	}
+	if _, err = decodeUint64(buf, r); err != nil { // Estimate ignored here
+		return err
+	}
 
 	c.Root = &CheckpointLevel{}
 	return c.Root.deserialize(buf, r)

internal/memstore/memstore.go

@@ -110,6 +110,35 @@ func (l *Level) free(t int64) (delme bool, n int) {
 	return len(l.metrics) == 0 && len(l.sublevels) == 0, n
 }
 
+// Return an estimate of how many values are stored for all metrics and sublevels between from and to.
+func (l *Level) countValues(from int64, to int64) int {
+	vals := 0
+	l.lock.RLock()
+	defer l.lock.RUnlock()
+
+	for _, c := range l.metrics {
+		for c != nil {
+			if to < c.start || c.end() < from {
+				continue
+			} else if c.start < from {
+				vals += int((from - c.start) / c.frequency)
+			} else if from < c.start {
+				vals += int((c.start - from) / c.frequency)
+			} else {
+				vals += len(c.data)
+			}
+
+			c = c.prev
+		}
+	}
+
+	for _, sublevel := range l.sublevels {
+		vals += sublevel.countValues(from, to)
+	}
+
+	return vals
+}
+
 type MemoryStore struct {
 	root Level // root of the tree structure
 	// TODO...

internal/memstore/streaming-checkpoint.go

@@ -17,6 +17,7 @@ func (ms *MemoryStore) SaveCheckpoint(from, to int64, w io.Writer) error {
 	buf = encodeBytes(buf, nil)
 	buf = encodeUint64(buf, uint64(from))
 	buf = encodeUint64(buf, uint64(to))
+	buf = encodeUint64(buf, uint64(ms.root.countValues(from, to)))
 
 	metricsbuf := make([]types.Float, 0, (to-from)/ms.MinFrequency()+1)
 	var err error
@@ -122,6 +123,13 @@ func (ms *MemoryStore) LoadCheckpoint(r io.Reader) error {
 	if _, err := decodeUint64(buf, r); err != nil { // To
 		return err
 	}
+	if valueEstimate, err := decodeUint64(buf, r); err != nil {
+		return err
+	} else {
+		if err := FillAllocatorCache(int(valueEstimate) * 8); err != nil {
+			return nil
+		}
+	}
 
 	if err := ms.root.loadCheckpoint(ms, r, buf); err != nil {
 		return err