You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: batch.go
    path of file: ./repos/rosedb
    
    the code of the file until where you have to start completion: package rosedb

import (
	"bytes"
	"fmt"
	"sync"
	"time"

	"github.com/bwmarrin/snowflake"
	"github.com/valyala/bytebufferpool"
)

// Batch is a batch operations of the database.
// If readonly is true, you can only get data from the batch by Get method.

    
func (b *Batch) Commit() error {
	defer b.unlock()
	if b.db.closed {
		return ErrDBClosed
	}

	if b.options.ReadOnly || len(b.pendingWrites) == 0 {
		return nil
	}

	b.mu.Lock()
	defer b.mu.Unlock()

	// check if committed or rollbacked
	if b.committed {
		return ErrBatchCommitted
	}
	if b.rollbacked {
		return ErrBatchRollbacked
	}

	batchId := b.batchId.Generate()
	now := time.Now().UnixNano()
	// write to wal buffer
	for _, record := range b.pendingWrites {
		buf := bytebufferpool.Get()
		b.buffers = append(b.buffers, buf)
		record.BatchId = uint64(batchId)
		encRecord := encodeLogRecord(record, b.db.encodeHeader, buf)
		b.db.dataFiles.PendingWrites(encRecord)
	}

	// write a record to indicate the end of the batch
	buf := bytebufferpool.Get()
	b.buffers = append(b.buffers, buf)
	endRecord := encodeLogRecord(&LogRecord{
		Key:  batchId.Bytes(),
		Type: LogRecordBatchFinished,
	}, b.db.encodeHeader, buf)
	b.db.dataFiles.PendingWrites(endRecord)

	// write to wal file
	chunkPositions, err := b.db.dataFiles.WriteAll()
	if err != nil {
		b.db.dataFiles.ClearPendingWrites()
		return err
	}
	if len(chunkPositions) != len(b.pendingWrites)+1 {
		panic("chunk positions length is not equal to pending writes length")
	}

	// flush wal if necessary
	if b.options.Sync && !b.db.options.Sync {
		if err := b.db.dataFiles.Sync(); err != nil {
			return err
		}
	}

	// write to index
	for i, record := range b.pendingWrites {
		if record.Type == LogRecordDeleted || record.IsExpired(now) {
			b.db.index.Delete(record.Key)
		} else {
			b.db.index.Put(record.Key, chunkPositions[i])
		}

		if b.db.options.WatchQueueSize > 0 {
			e := &Event{Key: record.Key, Value: record.Value, BatchId: record.BatchId}
			if record.Type == LogRecordDeleted {
				e.Action = WatchActionDelete
			} else {
				e.Action = WatchActionPut
			}
			b.db.watcher.putEvent(e)
		}
		// put the record back to the pool
		b.db.recordPool.Put(record)
	}

	b.committed = true
	return nil
}