From 24c1f21e4e281739ebc84831d4fb554e62ecd7b4 Mon Sep 17 00:00:00 2001
From: "j. Emrys Landivar (docmerlin)" <landivar@gmail.com>
Date: Fri, 2 Aug 2019 11:29:27 -0500
Subject: [PATCH] WIP

---
 query/stdlib/influxdata/influxdb/to.go |  8 +++-
 storage/points_writer.go               | 60 ++++++++++++++++++++++++++
 2 files changed, 67 insertions(+), 1 deletion(-)

diff --git a/query/stdlib/influxdata/influxdb/to.go b/query/stdlib/influxdata/influxdb/to.go
index 5e5f37eb48..0fbc3f270d 100644
--- a/query/stdlib/influxdata/influxdb/to.go
+++ b/query/stdlib/influxdata/influxdb/to.go
@@ -30,6 +30,7 @@ const ToKind = influxdb.ToKind
 // TODO(jlapacik) remove this once we have execute.DefaultFieldColLabel
 const defaultFieldColLabel = "_field"
 const DefaultMeasurementColLabel = "_measurement"
+const DefaultBufferSize = 1 << 14
 
 // ToOpSpec is the flux.OperationSpec for the `to` flux function.
 type ToOpSpec struct {
@@ -274,6 +275,7 @@ type ToTransformation struct {
 	spec               *ToProcedureSpec
 	implicitTagColumns bool
 	deps               ToDependencies
+	buf                *storage.BufferedPointsWriter
 }
 
 // RetractTable retracts the table for the transformation for the `to` flux function.
@@ -300,6 +302,7 @@ func NewToTransformation(ctx context.Context, d execute.Dataset, cache execute.T
 		spec:               spec,
 		implicitTagColumns: spec.Spec.TagColumns == nil,
 		deps:               deps,
+		buf:                storage.NewBufferedPointsWriter(DefaultBufferSize, deps.PointsWriter),
 	}, nil
 }
 
@@ -403,6 +406,9 @@ func (t *ToTransformation) UpdateProcessingTime(id execute.DatasetID, pt execute
 
 // Finish is called after the `to` flux function's transformation is done processing.
 func (t *ToTransformation) Finish(id execute.DatasetID, err error) {
+	if err == nil {
+		err = t.buf.Flush(t.ctx)
+	}
 	t.d.Finish(err)
 }
 
@@ -654,7 +660,7 @@ func writeTable(ctx context.Context, t *ToTransformation, tbl flux.Table) error
 				return err
 			}
 		}
-		return d.PointsWriter.WritePoints(ctx, points)
+		return t.buf.WritePoints(ctx, points)
 	})
 }
 
diff --git a/storage/points_writer.go b/storage/points_writer.go
index da98ddbcb0..e214ef9a1f 100644
--- a/storage/points_writer.go
+++ b/storage/points_writer.go
@@ -2,6 +2,7 @@ package storage
 
 import (
 	"context"
+	"sync"
 
 	"github.com/influxdata/influxdb/models"
 )
@@ -10,3 +11,62 @@ import (
 type PointsWriter interface {
 	WritePoints(context.Context, []models.Point) error
 }
+
+type BufferedPointsWriter struct {
+	sync.Mutex
+	buf []models.Point
+	n   int
+	wr  PointsWriter
+	err error
+}
+
+func NewBufferedPointsWriter(size int, pointswriter PointsWriter) *BufferedPointsWriter {
+	return &BufferedPointsWriter{
+		buf: make([]models.Point, size),
+		wr:  pointswriter,
+	}
+}
+
+// WritePoints writes the points to the underlying PointsWriter.
+func (b *BufferedPointsWriter) WritePoints(ctx context.Context, p []models.Point) error {
+	for len(p) > b.Available() && b.err == nil {
+		var n int
+		if b.Buffered() == 0 {
+			// Large write, empty buffer.
+			// Write directly from p to avoid copy.
+			b.err = b.wr.WritePoints(ctx, p)
+		} else {
+			b.n += copy(b.buf[b.n:], p)
+			b.err = b.Flush(ctx)
+		}
+		p = p[n:]
+	}
+	if b.err != nil {
+		return b.err
+	}
+	b.n += copy(b.buf[b.n:], p)
+	return nil
+}
+
+// Available returns how many models.Points are unused in the buffer.
+func (b *BufferedPointsWriter) Available() int { return len(b.buf) - b.n }
+
+// Buffered returns the number of models.Points that have been written into the current buffer.
+func (b *BufferedPointsWriter) Buffered() int { return len(b.buf) }
+
+// Flush writes any buffered data to the underlying PointsWriter.
+func (b *BufferedPointsWriter) Flush(ctx context.Context) error {
+	if b.err != nil {
+		return b.err
+	}
+	if b.n == 0 {
+		return nil
+	}
+
+	b.err = b.wr.WritePoints(ctx, b.buf[:b.n])
+	if b.err != nil {
+		return b.err
+	}
+	b.n = 0
+	return nil
+}