mysql: use numeric comparison for binlog filename (#547)

mysql: use numeric comparison for binlog filename

Author: lance6716

mysql/position.go

@@ -2,6 +2,8 @@ package mysql
 
 import (
 	"fmt"
+	"strconv"
+	"strings"
 )
 
 // For binlog filename + position based replication
@@ -12,22 +14,67 @@ type Position struct {
 
 func (p Position) Compare(o Position) int {
 	// First compare binlog name
-	if p.Name > o.Name {
+	nameCmp := CompareBinlogFileName(p.Name, o.Name)
+	if nameCmp != 0 {
+		return nameCmp
+	}
+	// Same binlog file, compare position
+	if p.Pos > o.Pos {
 		return 1
-	} else if p.Name < o.Name {
+	} else if p.Pos < o.Pos {
 		return -1
 	} else {
-		// Same binlog file, compare position
-		if p.Pos > o.Pos {
-			return 1
-		} else if p.Pos < o.Pos {
-			return -1
-		} else {
-			return 0
-		}
+		return 0
 	}
 }
 
 func (p Position) String() string {
 	return fmt.Sprintf("(%s, %d)", p.Name, p.Pos)
 }
+
+func CompareBinlogFileName(a, b string) int {
+	// sometimes it's convenient to construct a `Position` literal with no `Name`
+	if a == "" && b == "" {
+		return 0
+	} else if a == "" {
+		return -1
+	} else if b == "" {
+		return 1
+	}
+
+	splitBinlogName := func(n string) (string, int) {
+		// mysqld appends a numeric extension to the binary log base name to generate binary log file names
+		// ...
+		// If you supply an extension in the log name (for example, --log-bin=base_name.extension),
+		// the extension is silently removed and ignored.
+		// ref: https://dev.mysql.com/doc/refman/8.0/en/binary-log.html
+		i := strings.LastIndexByte(n, '.')
+		if i == -1 {
+			// try keeping backward compatibility
+			return n, 0
+		}
+
+		seq, err := strconv.Atoi(n[i+1:])
+		if err != nil {
+			panic(fmt.Sprintf("binlog file %s doesn't contain numeric extension", err))
+		}
+		return n[:i], seq
+	}
+
+	aBase, aSeq := splitBinlogName(a)
+	bBase, bSeq := splitBinlogName(b)
+
+	if aBase > bBase {
+		return 1
+	} else if aBase < bBase {
+		return -1
+	}
+
+	if aSeq > bSeq {
+		return 1
+	} else if aSeq < bSeq {
+		return -1
+	} else {
+		return 0
+	}
+}

mysql/position_test.go

@@ -0,0 +1,51 @@
+package mysql
+
+import (
+	"github.com/pingcap/check"
+)
+
+type positionCompareSuite struct {
+}
+
+var _ = check.Suite(&positionCompareSuite{})
+
+func (t *positionCompareSuite) TestPosCompare(c *check.C) {
+	ascendingPositions := []Position{
+		{
+			"",
+			4,
+		},
+		{
+			"",
+			100,
+		},
+		{
+			"mysql-bin.000001",
+			4,
+		},
+		{
+			"mysql-bin.000001",
+			100,
+		},
+		{
+			"mysql-bin.000002",
+			4,
+		},
+		{
+			"mysql-bin.999999",
+			4,
+		},
+		{
+			"mysql-bin.1000000",
+			4,
+		},
+	}
+
+	for i := 1; i < len(ascendingPositions); i++ {
+		c.Assert(ascendingPositions[i-1].Compare(ascendingPositions[i]), check.Equals, -1)
+	}
+
+	for _, p := range ascendingPositions {
+		c.Assert(p.Compare(p), check.Equals, 0)
+	}
+}