streaming checkpoints

internal/memstore/checkpoints.go

@@ -250,7 +250,7 @@ func encodeUint32(buf []byte, i uint32) []byte {
 		byte((i>>24)&0xff))
 }
 
-func decodeBytes(buf []byte, r *bufio.Reader) ([]byte, error) {
+func decodeBytes(buf []byte, r io.Reader) ([]byte, error) {
 	len, err := decodeUint32(buf, r)
 	if err != nil {
 		return nil, err
@@ -267,7 +267,7 @@ func decodeBytes(buf []byte, r *bufio.Reader) ([]byte, error) {
 	return bytes, nil
 }
 
-func decodeString(buf []byte, r *bufio.Reader) (string, error) {
+func decodeString(buf []byte, r io.Reader) (string, error) {
 	len, err := decodeUint32(buf, r)
 	if err != nil {
 		return "", err
@@ -286,7 +286,7 @@ func decodeString(buf []byte, r *bufio.Reader) (string, error) {
 	return string(bytes), nil
 }
 
-func decodeUint64(buf []byte, r *bufio.Reader) (uint64, error) {
+func decodeUint64(buf []byte, r io.Reader) (uint64, error) {
 	buf = buf[0:8]
 	_, err := io.ReadFull(r, buf)
 	if err != nil {
@@ -303,7 +303,7 @@ func decodeUint64(buf []byte, r *bufio.Reader) (uint64, error) {
 		(uint64(buf[7]) << 56), nil
 }
 
-func decodeUint32(buf []byte, r *bufio.Reader) (uint32, error) {
+func decodeUint32(buf []byte, r io.Reader) (uint32, error) {
 	buf = buf[0:4]
 	_, err := io.ReadFull(r, buf)
 	if err != nil {

internal/memstore/chunks.go

@@ -16,15 +16,14 @@ type chunk struct {
 }
 
 func newChunk(ts, freq int64) *chunk {
-	b := &chunk{}
+	return &chunk{
-	b.frequency = freq
+		frequency:    freq,
-	b.start = ts - (freq / 2)
+		start:        ts - (freq / 2),
-	b.prev = nil
+		prev:         nil,
-	b.next = nil
+		next:         nil,
-	b.checkpointed = false
+		checkpointed: false,
-	b.data = RequestFloatSlice(bufferSizeInFloats)
+		data:         RequestFloatSlice(bufferSizeInFloats)[:0],
-	b.data = b.data[:0]
+	}
-	return b
 }
 
 func freeChunk(c *chunk) {

internal/memstore/memstore.go

@@ -91,6 +91,8 @@ func (l *level) free(t int64) (delme bool, n int) {
 type MemoryStore struct {
 	root level // root of the tree structure
 	// TODO...
+
+	metrics map[string]int // TODO...
 }
 
 func (ms *MemoryStore) GetOffset(metric string) int {
@@ -100,3 +102,7 @@ func (ms *MemoryStore) GetOffset(metric string) int {
 func (ms *MemoryStore) GetMetricForOffset(offset int) string {
 	return "" // TODO!
 }
+
+func (ms *MemoryStore) MinFrequency() int64 {
+	return 10 // TODO
+}

internal/memstore/streaming-checkpoint.go

@@ -1,6 +1,7 @@
 package memstore
 
 import (
+	"fmt"
 	"io"
 	"reflect"
 	"unsafe"
@@ -8,7 +9,29 @@ import (
 	"github.com/ClusterCockpit/cc-metric-store/internal/types"
 )
 
-func (l *level) streamingCheckpoint(ms *MemoryStore, from, to int64, w io.Writer, buf []byte, metricsbuf []types.Float) ([]byte, error) {
+// Can be done in parallel with other operations, but is single threaded itself.
+func (ms *MemoryStore) SaveCheckpoint(from, to int64, w io.Writer) error {
+	// Header:
+	buf := make([]byte, 0, writeBufferSize*2)
+	buf = append(buf, magicValue...)
+	buf = encodeBytes(buf, nil)
+	buf = encodeUint64(buf, uint64(from))
+	buf = encodeUint64(buf, uint64(to))
+
+	metricsbuf := make([]types.Float, 0, (to-from)/ms.MinFrequency()+1)
+	var err error
+	if buf, err = ms.root.saveCheckpoint(ms, from, to, w, buf, metricsbuf); err != nil {
+		return err
+	}
+
+	if _, err := w.Write(buf); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+func (l *level) saveCheckpoint(ms *MemoryStore, from, to int64, w io.Writer, buf []byte, metricsbuf []types.Float) ([]byte, error) {
 	var err error
 	l.lock.RLock()
 	defer l.lock.RUnlock()
@@ -52,7 +75,7 @@ func (l *level) streamingCheckpoint(ms *MemoryStore, from, to int64, w io.Writer
 	buf = encodeUint32(buf, uint32(len(l.sublevels)))
 	for key, sublevel := range l.sublevels {
 		buf = encodeString(buf, key)
-		buf, err = sublevel.streamingCheckpoint(ms, from, to, w, buf, metricsbuf)
+		buf, err = sublevel.saveCheckpoint(ms, from, to, w, buf, metricsbuf)
 		if err != nil {
 			return nil, err
 		}
@@ -60,3 +83,136 @@ func (l *level) streamingCheckpoint(ms *MemoryStore, from, to int64, w io.Writer
 
 	return buf, nil
 }
+
+func (ms *MemoryStore) LoadCheckpoint(r io.Reader) error {
+	buf := make([]byte, len(magicValue), 64)
+	if _, err := io.ReadFull(r, buf); err != nil {
+		return err
+	}
+
+	if string(buf) != magicValue {
+		return fmt.Errorf("file corrupted: expected the file to start with %#v (got %#v)", magicValue, string(buf))
+	}
+
+	if _, err := decodeBytes(buf, r); err != nil { // Reserved
+		return err
+	}
+	if _, err := decodeUint64(buf, r); err != nil { // From
+		return err
+	}
+	if _, err := decodeUint64(buf, r); err != nil { // To
+		return err
+	}
+
+	if err := ms.root.loadCheckpoint(ms, r, buf); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+// Blocks all other accesses for this level and all its sublevels!
+func (l *level) loadCheckpoint(ms *MemoryStore, r io.Reader, buf []byte) error {
+	l.lock.Lock()
+	defer l.lock.Unlock()
+
+	var n uint32
+	var err error
+	var key string
+	if _, err = decodeBytes(buf, r); err != nil { // Reserved...
+		return err
+	}
+
+	// Metrics:
+	if n, err = decodeUint32(buf, r); err != nil {
+		return err
+	}
+	for i := 0; i < int(n); i++ {
+		if key, err = decodeString(buf, r); err != nil {
+			return err
+		}
+		if l.metrics == nil {
+			l.metrics = make([]*chunk, len(ms.metrics))
+		}
+
+		// Metric:
+		if _, err = decodeBytes(buf, r); err != nil { // Reserved...
+			return err
+		}
+		var freq, from uint64
+		if freq, err = decodeUint64(buf, r); err != nil {
+			return err
+		}
+		if from, err = decodeUint64(buf, r); err != nil {
+			return err
+		}
+		numelements, err := decodeUint32(buf, r)
+		if err != nil {
+			return err
+		}
+
+		var x types.Float
+		elmsize := unsafe.Sizeof(x)
+		bytes := RequestBytes(int(elmsize) * int(numelements))
+		if _, err = io.ReadFull(r, bytes); err != nil {
+			return fmt.Errorf("loading metric %#v: %w", key, err)
+		}
+
+		offset := ms.GetOffset(key)
+		if offset == -1 {
+			// Skip unkown metrics
+			ReleaseBytes(bytes)
+			continue
+		}
+
+		sh := (*reflect.SliceHeader)(unsafe.Pointer(&bytes))
+		chunk := &chunk{
+			frequency:    int64(freq),
+			start:        int64(from),
+			prev:         nil,
+			next:         nil,
+			data:         unsafe.Slice((*types.Float)(unsafe.Pointer(sh.Data)), numelements),
+			checkpointed: true,
+		}
+
+		if prevchunk := l.metrics[offset]; prevchunk != nil {
+			if prevchunk.end() > chunk.start {
+				return fmt.Errorf(
+					"loading metric %#v: loaded checkpoint overlaps with other chunks or is not loaded in correct order (%d - %d)",
+					key, prevchunk.start, chunk.start)
+			}
+			prevchunk.next = chunk
+			chunk.prev = prevchunk
+			l.metrics[offset] = chunk
+		} else {
+			l.metrics[offset] = chunk
+		}
+	}
+
+	// Sublevels:
+	if n, err = decodeUint32(buf, r); err != nil {
+		return err
+	}
+	for i := 0; i < int(n); i++ {
+		if key, err = decodeString(buf, r); err != nil {
+			return err
+		}
+		if l.sublevels == nil {
+			l.sublevels = make(map[string]*level, n)
+		}
+		sublevel, ok := l.sublevels[key]
+		if !ok {
+			sublevel = &level{}
+		}
+
+		if err = sublevel.loadCheckpoint(ms, r, buf); err != nil {
+			return fmt.Errorf("loading sublevel %#v: %w", key, err)
+		}
+
+		if !ok {
+			l.sublevels[key] = sublevel
+		}
+	}
+
+	return nil
+}

internal/types/types.go

@@ -0,0 +1,8 @@
+package types
+
+type Stats struct {
+	Samples int   `json:"samples"`
+	Min     Float `json:"min"`
+	Avg     Float `json:"avg"`
+	Max     Float `json:"max"`
+}