leveldb.go

// Copyright 2019 Finobo
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package ldbstore

import (
	"github.com/syndtr/goleveldb/leveldb"
	ldberr "github.com/syndtr/goleveldb/leveldb/errors"
	"github.com/syndtr/goleveldb/leveldb/filter"
	"github.com/syndtr/goleveldb/leveldb/opt"
)

const (
	// minCache is the minimum amount of memory in megabytes to allocate to leveldb
	// read and write caching, split half and half.
	minCache = 16

	// minHandles is the minimum number of files handles to allocate to the open
	// database files.
	minHandles = 16
)

// New returns a wrapped LevelDB object.
func New(file string, cache, handles int) (*Database, error) {
	// Ensure we have some minimal caching and file guarantees
	if cache < minCache {
		cache = minCache
	}
	if handles < minHandles {
		handles = minHandles
	}

	// Open the db and recover any potential corruptions
	db, err := leveldb.OpenFile(file, &opt.Options{
		OpenFilesCacheCapacity: handles,
		BlockCacheCapacity:     cache / 2 * opt.MiB,
		WriteBuffer:            cache / 4 * opt.MiB, // Two of these are used internally
		Filter:                 filter.NewBloomFilter(10),
	})
	if ldberr.IsCorrupted(err) {
		db, err = leveldb.RecoverFile(file, nil)
	}
	if err != nil {
		return nil, err
	}
	// Assemble the wrapper with all the registered metrics
	ldb := &Database{
		fn: file,
		db: db,
	}

	return ldb, nil
}

// Close stops the metrics collection, flushes any pending data to disk and closes
// all io accesses to the underlying key-value store.
func (db *Database) Close() error {
	return db.db.Close()
}

// Database is a persistent key-value store. Apart from basic data storage
// functionality it also supports batch writes and iterating over the keyspace in
// binary-alphabetical order.
type Database struct {
	fn string      // filename for reporting
	db *leveldb.DB // LevelDB instance
}