const.go

// Copyright 2021 hardcore-os Project Authors
//
// 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 utils

import (
	"hash/crc32"
	"math"
	"os"
)

const (
	// MaxLevelNum _
	MaxLevelNum = 7
	// DefaultValueThreshold _
	DefaultValueThreshold = 1024
)

// file
const (
	ManifestFilename                  = "MANIFEST"
	ManifestRewriteFilename           = "REWRITEMANIFEST"
	ManifestDeletionsRewriteThreshold = 10000
	ManifestDeletionsRatio            = 10
	DefaultFileFlag                   = os.O_RDWR | os.O_CREATE | os.O_APPEND
	DefaultFileMode                   = 0666
	MaxValueLogSize                   = 10 << 20
	// This is O_DSYNC (datasync) on platforms that support it -- see file_unix.go
	datasyncFileFlag = 0x0
	// 基于可变长编码,其最可能的编码
	MaxHeaderSize          = 21
	VlogHeaderSize         = 0
	MaxVlogFileSize uint32 = math.MaxUint32
	Mi              int64  = 1 << 20
	KVWriteChCapacity = 1000
)

// meta
const (
	BitDelete       byte = 1 << 0 // Set if the key has been deleted.
	BitValuePointer byte = 1 << 1 // Set if the value is NOT stored directly next to key.
)

// codec
var (
	MagicText    = [4]byte{'H', 'A', 'R', 'D'}
	MagicVersion = uint32(1)
	// CastagnoliCrcTable is a CRC32 polynomial table
	CastagnoliCrcTable = crc32.MakeTable(crc32.Castagnoli)
)