db: improve metrics formatting

This change improves the formatting of the Pebble metrics:
 - we no longer try to artificially fit non-tabular information in a
   single table
 - all byte figures end in B/KB/MB/etc
 - counts and corresponding sizes are grouped together
 - flushable ingests information moved under ingestions

These metrics are periodically logged and can be obtained through the
db console as well.

Release note: Pebble metrics formatting improvements; tools that parse
these logs might need updating.

Fixes cockroachdb#1473.

internal/humanize/humanize.go

@@ -41,6 +41,12 @@ var IEC = config{1024, []string{" B", " K", " M", " G", " T", " P", " E"}}
 // SI produces human readable representations of integer values in SI units.
 var SI = config{1000, []string{"", " K", " M", " G", " T", " P", " E"}}
 
+// Bytes produces human readable representations of byte values in IEC units.
+var Bytes = config{1024, []string{"B", "KB", "MB", "GB", "TB", "PB", "EB"}}
+
+// Count produces human readable representations of unitless values in SI units.
+var Count = config{1000, []string{"", "K", "M", "G", "T", "P", "E"}}
+
 // Int64 produces a human readable representation of the value.
 func (c *config) Int64(s int64) FormattedString {
 	if s < 0 {

internal/humanize/humanize_test.go

@@ -0,0 +1,38 @@
+// Copyright 2023 The LevelDB-Go and Pebble Authors. All rights reserved. Use
+// of this source code is governed by a BSD-style license that can be found in
+// the LICENSE file.
+
+package humanize
+
+import (
+	"bytes"
+	"fmt"
+	"strconv"
+	"strings"
+	"testing"
+
+	"github.com/cockroachdb/datadriven"
+)
+
+func TestHumanize(t *testing.T) {
+	datadriven.RunTest(t, "testdata/humanize", func(t *testing.T, td *datadriven.TestData) string {
+		var c config
+		switch td.Cmd {
+		case "bytes":
+			c = Bytes
+		case "count":
+			c = Count
+		default:
+			td.Fatalf(t, "invalid command %q", td.Cmd)
+		}
+		var buf bytes.Buffer
+		for _, row := range strings.Split(td.Input, "\n") {
+			val, err := strconv.ParseInt(row, 10, 64)
+			if err != nil {
+				td.Fatalf(t, "error parsing %q: %v", row, err)
+			}
+			fmt.Fprintf(&buf, "%s\n", c.Int64(val))
+		}
+		return buf.String()
+	})
+}

internal/humanize/testdata/humanize

@@ -0,0 +1,49 @@
+bytes
+0
+1
+9
+99
+123
+123456
+12345678
+1234567890
+1234567890123
+123456789012345
+123456789012345678
+----
+0B
+1B
+9B
+99B
+123B
+121KB
+12MB
+1.1GB
+1.1TB
+112TB
+110PB
+
+count
+0
+1
+9
+99
+123
+123456
+12345678
+1234567890
+1234567890123
+123456789012345
+123456789012345678
+----
+0
+1
+9
+99
+123
+124K
+12M
+1.2G
+1.2T
+124T
+124P