mysql: use numeric comparison for binlog filename (go-mysql-org#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)
+}
+}