From 1fee39f343954ca7501a6b8f25abd9f86eaf618b Mon Sep 17 00:00:00 2001
From: Benoit Sigoure <tsunanet@gmail.com>
Date: Mon, 10 Jun 2024 13:31:08 +0200
Subject: [PATCH] region: add a metric to track bytes written to the wire per
 RPC call

---
 region/client.go     |  1 +
 region/compressor.go |  6 +++---
 region/prometheus.go | 12 ++++++++++++
 3 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/region/client.go b/region/client.go
index 7336b66d..00297e1a 100644
--- a/region/client.go
+++ b/region/client.go
@@ -658,6 +658,7 @@ func (c *client) send(rpc hrpc.Call) (uint32, error) {
 		return id, err
 	}
 
+	rpcSize.WithLabelValues(c.Addr()).Observe(float64(uint32(len(b)) + cellblocksLen))
 	if cellblocks != nil {
 		bfs := append(net.Buffers{b}, cellblocks...)
 		_, err = bfs.WriteTo(c.conn)
diff --git a/region/compressor.go b/region/compressor.go
index 7a27d449..6e6cb10b 100644
--- a/region/compressor.go
+++ b/region/compressor.go
@@ -38,9 +38,9 @@ func resizeBufferCap(b []byte, capacity int) []byte {
 		return b
 	}
 
-	l := len(b)
-	b = append(b, make([]byte, capacity-l)...)
-	return b[:l]
+	b2 := make([]byte, capacity)
+	copy(b2, b)
+	return b2[:len(b)]
 }
 
 func (c *compressor) compressCellblocks(cbs net.Buffers, uncompressedLen uint32) []byte {
diff --git a/region/prometheus.go b/region/prometheus.go
index 4d0cbf81..56025df1 100644
--- a/region/prometheus.go
+++ b/region/prometheus.go
@@ -29,4 +29,16 @@ var (
 		},
 		[]string{"regionserver"},
 	)
+
+	rpcSize = promauto.NewHistogramVec(
+		prometheus.HistogramOpts{
+			Namespace: "gohbase",
+			Name:      "rpc_size_bytes",
+			Help:      "Number of bytes sent per RPC call to HBase",
+			// >>> [1024*(4**i) for i in range(8)]
+			// [1024, 4096, 16384, 65536, 262144, 1048576, 4194304, 16777216]
+			Buckets: prometheus.ExponentialBuckets(1024, 4, 8),
+		},
+		[]string{"regionserver"},
+	)
 )