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: db.go
    path of file: ./repos/lotusdb
    
    the code of the file until where you have to start completion: package lotusdb

import (
	"context"
	"fmt"
	"io"
	"log"
	"os"
	"os/signal"
	"path/filepath"
	"reflect"
	"sync"
	"syscall"
	"time"

	"github.com/dgraph-io/badger/v4/y"
	"github.com/gofrs/flock"
	"github.com/rosedblabs/diskhash"
	"github.com/rosedblabs/wal"
	"golang.org/x/sync/errgroup"
)

const (
	fileLockName = "FLOCK"
)

// DB is the m
    
func (db *DB) flushMemtable(table *memtable) {
	db.flushLock.Lock()
	defer db.flushLock.Unlock()
	sklIter := table.skl.NewIterator()
	var deletedKeys [][]byte
	var logRecords []*ValueLogRecord

	// iterate all records in memtable, divide them into deleted keys and log records
	for sklIter.SeekToFirst(); sklIter.Valid(); sklIter.Next() {
		key, valueStruct := y.ParseKey(sklIter.Key()), sklIter.Value()
		if valueStruct.Meta == LogRecordDeleted {
			deletedKeys = append(deletedKeys, key)
		} else {
			logRecord := ValueLogRecord{key: key, value: valueStruct.Value}
			logRecords = append(logRecords, &logRecord)
		}
	}
	_ = sklIter.Close()

	// write to value log, get the positions of keys
	keyPos, err := db.vlog.writeBatch(logRecords)
	if err != nil {
		log.Println("vlog writeBatch failed:", err)
		return
	}

	// sync the value log
	if err := db.vlog.sync(); err != nil {
		log.Println("vlog sync failed:", err)
		return
	}

	// write all keys and positions to index
	var putMatchKeys []diskhash.MatchKeyFunc
	if db.options.IndexType == Hash && len(keyPos) > 0 {
		putMatchKeys = make([]diskhash.MatchKeyFunc, len(keyPos))
		for i := range putMatchKeys {
			putMatchKeys[i] = MatchKeyFunc(db, keyPos[i].key, nil, nil)
		}
	}
	if err := db.index.PutBatch(keyPos, putMatchKeys...); err != nil {
		log.Println("index PutBatch failed:", err)
		return
	}
	// delete the deleted keys from index
	var deleteMatchKeys []diskhash.MatchKeyFunc
	if db.options.IndexType == Hash && len(deletedKeys) > 0 {
		deleteMatchKeys = make([]diskhash.MatchKeyFunc, len(deletedKeys))
		for i := range deleteMatchKeys {
			deleteMatchKeys[i] = MatchKeyFunc(db, deletedKeys[i], nil, nil)
		}
	}
	if err := db.index.DeleteBatch(deletedKeys, deleteMatchKeys...); err != nil {
		log.Println("index DeleteBatch failed:", err)
		return
	}
	// sync the index
	if err := db.index.Sync(); err != nil {
		log.Println("index sync failed:", err)
		return
	}

	// delete the wal
	if err := table.deleteWAl(); err != nil {
		log.Println("delete wal failed:", err)
		return
	}

	// delete old memtable kept in memory
	db.mu.Lock()
	if table == db.activeMem {
		options := db.activeMem.options
		options.tableId++
		// open a new memtable for writing
		table, err := openMemtable(options)
		if err != nil {
			panic("flush activate memtable wrong")
		}
		db.activeMem = table
	} else {
		if len(db.immuMems) == 1 {
			db.immuMems = db.immuMems[:0]
		} else {
			db.immuMems = db.immuMems[1:]
		}
	}

	db.mu.Unlock()
}