Snowflake ID란? Kotlin으로 직접 구현하기

val id1 = SnowflakeIdGenerator.nextId() // "3qkpc7gh8n4m2" Thread.sleep(100) val id2 = SnowflakeIdGenerator.nextId() // "3qkpc7gh8n4m5" Thread.sleep(100) val id3 = SnowflakeIdGenerator.nextId() // "3qkpc7gh8n4m8" println(id1 < id2) // true println(id2 < id3) // true val ids = mutableListOf(id3, id1, id2) ids.sort() // 결과: [id1, id2, id3] - 생성 시간 순서대로 정렬됨!

-- 최신 글부터 조회 SELECT * FROM posts ORDER BY id DESC; -- 특정 시간 이후의 데이터 조회 SELECT * FROM posts WHERE id > '3qkpc7gh8n4m2';

import java.net.NetworkInterface import java.security.SecureRandom import java.nio.ByteBuffer object SnowflakeIdGenerator { // 기준 시간 (2010년 11월 4일 01:42:54.657 UTC) - Twitter Snowflake epoch private const val EPOCH = 1288834974657L // 비트 할당 private const val TIMESTAMP_BITS = 41 private const val MACHINE_ID_BITS = 10 private const val SEQUENCE_BITS = 12 // 최대값 private const val MAX_MACHINE_ID = (1L shl MACHINE_ID_BITS) - 1 private const val MAX_SEQUENCE = (1L shl SEQUENCE_BITS) - 1 // 비트 시프트 private const val TIMESTAMP_SHIFT = MACHINE_ID_BITS + SEQUENCE_BITS private const val MACHINE_ID_SHIFT = SEQUENCE_BITS // Crockford Base32 알파벳 (혼동하기 쉬운 문자 제외) private const val CROCKFORD_ALPHABET = "0123456789abcdefghjkmnpqrstvwxyz" private val machineId: Long = generateMachineId() private var sequence: Long = SecureRandom().nextInt(MAX_SEQUENCE.toInt()).toLong() private var lastTimestamp: Long = -1 private fun generateMachineId(): Long { return try { val networkInterface = NetworkInterface.getNetworkInterfaces() .asSequence() .filter { !it.isLoopback && it.hardwareAddress != null } .firstOrNull() if (networkInterface != null) { val mac = networkInterface.hardwareAddress val macValue = mac.take(3).fold(0L) { acc, byte -> (acc shl 8) or (byte.toInt() and 0xFF).toLong() } (macValue xor ProcessHandle.current().pid()) and MAX_MACHINE_ID } else { SecureRandom().nextInt(MAX_MACHINE_ID.toInt()).toLong() } } catch (e: Exception) { SecureRandom().nextInt(MAX_MACHINE_ID.toInt()).toLong() } } @Synchronized fun nextId(): String { var timestamp = System.currentTimeMillis() if (timestamp < lastTimestamp) { throw RuntimeException("Clock moved backwards. Refusing to generate id") } if (timestamp == lastTimestamp) { sequence = (sequence + 1) and MAX_SEQUENCE if (sequence == 0L) { timestamp = waitNextMillis(lastTimestamp) } } else { // MongoDB 스타일: 시퀀스 계속 증가 sequence = (sequence + 1) and MAX_SEQUENCE } lastTimestamp = timestamp val id = ((timestamp - EPOCH) shl TIMESTAMP_SHIFT) or (machineId shl MACHINE_ID_SHIFT) or sequence return encodeCrockfordBase32(id) } private fun encodeCrockfordBase32(value: Long): String { // Big-endian으로 저장하여 시간순 정렬 보장 val bytes = ByteBuffer.allocate(8).putLong(value).array() val result = StringBuilder() var buffer = 0 var bitsInBuffer = 0 for (byte in bytes) { buffer = (buffer shl 8) or (byte.toInt() and 0xFF) bitsInBuffer += 8 while (bitsInBuffer >= 5) { val index = (buffer ushr (bitsInBuffer - 5)) and 0x1F result.append(CROCKFORD_ALPHABET[index]) bitsInBuffer -= 5 } } if (bitsInBuffer > 0) { val index = (buffer shl (5 - bitsInBuffer)) and 0x1F result.append(CROCKFORD_ALPHABET[index]) } return result.toString() } private fun decodeCrockfordBase32(encoded: String): Long { var buffer = 0L var bitsInBuffer = 0 val bytes = ByteArray(8) var byteIndex = 0 for (char in encoded.lowercase()) { // 혼동하기 쉬운 문자 자동 변환 val index = when (char) { 'o' -> CROCKFORD_ALPHABET.indexOf('0') 'i', 'l' -> CROCKFORD_ALPHABET.indexOf('1') else -> CROCKFORD_ALPHABET.indexOf(char) } if (index == -1) { throw IllegalArgumentException("Invalid character: $char") } buffer = (buffer shl 5) or index.toLong() bitsInBuffer += 5 while (bitsInBuffer >= 8 && byteIndex < 8) { bytes[byteIndex++] = ((buffer ushr (bitsInBuffer - 8)) and 0xFF).toByte() bitsInBuffer -= 8 } } return ByteBuffer.wrap(bytes).getLong() } private fun waitNextMillis(lastTimestamp: Long): Long { var timestamp = System.currentTimeMillis() while (timestamp <= lastTimestamp) { timestamp = System.currentTimeMillis() } return timestamp } fun parseId(base32Id: String): SnowflakeIdInfo { val id = decodeCrockfordBase32(base32Id) val timestamp = (id shr TIMESTAMP_SHIFT) + EPOCH val machineId = (id shr MACHINE_ID_SHIFT) and MAX_MACHINE_ID val sequence = id and MAX_SEQUENCE return SnowflakeIdInfo(id, base32Id, timestamp, machineId, sequence) } fun getMachineId(): Long = machineId data class SnowflakeIdInfo( val id: Long, val base32Id: String, val timestamp: Long, val machineId: Long, val sequence: Long, ) }

// ID 생성 (초기화 불필요) val id = SnowflakeIdGenerator.nextId() // 결과: "3qkpc7gh8n4m2" // ID 정보 파싱 val info = SnowflakeIdGenerator.parseId(id) println(info.timestamp) // 생성 시간 println(info.machineId) // 머신 ID println(info.sequence) // 시퀀스 번호