GH-41159: [Go][Parquet] Improvement Parquet BitWriter WriteVlqInt Per…

…formance (#41160)

[GH-41159](#41159)
### Rationale for this change

This change improves Parquet FileWriter performance while writing parquets from arrow Records.
We saw a speed improvement from writing 320k rows/sec -> 650 rows/sec after making this change.

### What changes are included in this PR?
This PR reuses the `buf` variable being used by the bitWriter when writing parquet files.

### Are these changes tested?
Yes

### Are there any user-facing changes?
No

Authored-by: @ hhoughgg 

* GitHub Issue: #41159

Lead-authored-by: Andy Fan <[email protected]>
Co-authored-by: andyfan <[email protected]>
Signed-off-by: Matt Topol <[email protected]>

go/parquet/internal/utils/bit_reader_test.go

@@ -59,6 +59,23 @@ func TestBitWriter(t *testing.T) {
 
 	assert.Equal(t, byte(0xAA), buf[0])
 	assert.Equal(t, byte(0xCC), buf[1])
+
+	for i := 0; i < 3; i++ {
+		assert.True(t, bw.WriteVlqInt(uint64(i)))
+	}
+	assert.Equal(t, byte(0xAA), buf[0])
+	assert.Equal(t, byte(0xCC), buf[1])
+	assert.Equal(t, byte(0), buf[2])
+	assert.Equal(t, byte(1), buf[3])
+	assert.Equal(t, byte(2), buf[4])
+}
+
+func BenchmarkBitWriter(b *testing.B) {
+	buf := make([]byte, b.N)
+	bw := utils.NewBitWriter(utils.NewWriterAtBuffer(buf))
+	for i := 0; i < b.N; i++ {
+		assert.True(b, bw.WriteVlqInt(uint64(1)))
+	}
 }
 
 func TestBitReader(t *testing.T) {

go/parquet/internal/utils/bit_writer.go

@@ -75,6 +75,7 @@ type BitWriter struct {
 	byteoffset int
 	bitoffset  uint
 	raw        [8]byte
+	buf        [binary.MaxVarintLen64]byte
 }
 
 // NewBitWriter initializes a new bit writer to write to the passed in interface
@@ -163,9 +164,8 @@ func (b *BitWriter) WriteAligned(val uint64, nbytes int) bool {
 // without buffering.
 func (b *BitWriter) WriteVlqInt(v uint64) bool {
 	b.Flush(true)
-	var buf [binary.MaxVarintLen64]byte
-	nbytes := binary.PutUvarint(buf[:], v)
-	if _, err := b.wr.WriteAt(buf[:nbytes], int64(b.byteoffset)); err != nil {
+	nbytes := binary.PutUvarint(b.buf[:], v)
+	if _, err := b.wr.WriteAt(b.buf[:nbytes], int64(b.byteoffset)); err != nil {
 		log.Println(err)
 		return false
 	}