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158 lines
5.5 KiB
Markdown
158 lines
5.5 KiB
Markdown
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# Snowflake
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## Algorithm Introduction
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`Snowflake` is a distributed global unique ID generation algorithm proposed by twitter. The result of the algorithm generating `ID` is a long integer with the size of `64bit` . Under the standard algorithm, its structure is shown in the figure below:
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![snowflake](imgs/snowflake.jpeg)
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-`One bit`, unused.
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- The highest bit in the binary system is the sign bit. The `ID` generated by us is generally a positive integer, so the highest bit is fixed to 0.
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- `41 bits` to record the timestamp (MS).
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- `41 bits` can represent `2^41 - 1` numbers.
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- In other words, `41 bits` can represent the value of `2^41 - 1` milliseconds, and the unit year is `(2^41 - 1) / (1000 * 60 * 60 * 24 * 365)` about `69` years。
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- `10 bits`, used to record the `ID` of the working machine.
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- It can be deployed in `2^10` nodes, including `5` bits `DatacenterId` and `5` bits `WorkerId`.
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- `12 bits`, serial number, used to record different `id` generated in the same millisecond.
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- `12 bits` can represent the maximum number of positive integers `2^12 - 1` with a total of `4095` numbers, which represent the `4095` `ID` serial numbers generated by the same machine in the same time interval (MS).
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`Snowflake` can guarantee that:
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- All generated `ID` increase with time trend.
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- No duplicate `ID` will be generated in the whole distributed system (Because there is a distinction between `DatacenterId (5 bits)` and `WorkerId (5 bits)`.
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The [hyperf/snowflake](https://github.com/hyperf/snowflake) component provides good extensibility in design, allowing you to implement other variant algorithms based on snowflake with simple extension.
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## Install
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```
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composer require hyperf/snowflake
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```
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## Use
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The framework provides `MetaGeneratorInterface` and `IdGeneratorInterface`. `MetaGeneratorInterface` generates `Meta` files of `ID`, and `IdGeneratorInterface` generates `distributed ID` based on the corresponding `Meta` files.
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The `MetaGeneratorInterface` used by the framework by default is a `millisecond level generator` based on `Redis`.
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The configuration file is located in `config/autoload/snowflake.php` If the configuration file does not exist, you can execute `php bin/hyperf.php vendor:publish hyperf/snowflake` command to create a default configuration. The contents of the configuration file are as follows:
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```php
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<?php
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declare(strict_types=1);
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use Hyperf\Snowflake\MetaGenerator\RedisMilliSecondMetaGenerator;
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use Hyperf\Snowflake\MetaGenerator\RedisSecondMetaGenerator;
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use Hyperf\Snowflake\MetaGeneratorInterface;
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return [
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'begin_second' => MetaGeneratorInterface::DEFAULT_BEGIN_SECOND,
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RedisMilliSecondMetaGenerator::class => [
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// Redis Pool
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'pool' => 'default',
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// To calculate the Key of WorkerId
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'key' => RedisMilliSecondMetaGenerator::DEFAULT_REDIS_KEY
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],
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RedisSecondMetaGenerator::class => [
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// Redis Pool
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'pool' => 'default',
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// To calculate the Key of WorkerId
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'key' => RedisMilliSecondMetaGenerator::DEFAULT_REDIS_KEY
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],
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];
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```
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Using `Snowflake` in the framework is very simple. You just need to take out the `IdGeneratorInterface` object from `DI`.
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```php
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<?php
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use Hyperf\Snowflake\IdGeneratorInterface;
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use Hyperf\Utils\ApplicationContext;
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$container = ApplicationContext::getContainer();
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$generator = $container->get(IdGeneratorInterface::class);
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$id = $generator->generate();
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```
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When you know that the `ID` needs to reverse the corresponding `Meta`, you just need to call `generate`.
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```php
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<?php
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use Hyperf\Snowflake\IdGeneratorInterface;
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use Hyperf\Utils\ApplicationContext;
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$container = ApplicationContext::getContainer();
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$generator = $container->get(IdGeneratorInterface::class);
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$meta = $generator->degenerate($id);
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```
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## Override 'Meta' generator
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There are many ways to implement the `distributed global unique ID`, and there are also many variants based on the `Snowflake` algorithm. Although they are all `Snowflake` algorithms, they are not the same. For example, someone may generate a `Meta` based on `UserId` rather than `WorkerId`. Next, let's implement a simple `MetaGenerator`.
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In short, the `UserId` will definitely exceed '10 bits'. Therefore, the default `DataCenterId` and `WorkerId` cannot be installed. Therefore, the `UserId` module needs to be taken.
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```php
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<?php
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declare(strict_types=1);
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use Hyperf\Snowflake\IdGenerator;
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class UserDefinedIdGenerator
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{
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/**
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* @var IdGenerator\SnowflakeIdGenerator
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*/
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protected $idGenerator;
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public function __construct(IdGenerator\SnowflakeIdGenerator $idGenerator)
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{
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$this->idGenerator = $idGenerator;
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}
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public function generate(int $userId)
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{
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$meta = $this->idGenerator->getMetaGenerator()->generate();
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return $this->idGenerator->generate($meta->setWorkerId($userId % 31));
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}
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public function degenerate(int $id)
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{
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return $this->idGenerator->degenerate($id);
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}
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}
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use Hyperf\Utils\ApplicationContext;
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$container = ApplicationContext::getContainer();
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$generator = $container->get(UserDefinedIdGenerator::class);
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$userId = 20190620;
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$id = $generator->generate($userId);
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```
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## Application in database modelon in database model
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After configuring `Snowflake`, we can make the database model directly use `Snowflake` `ID` as the primary key.
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```php
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<?php
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class User extends \Hyperf\Database\Model\Model {
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use \Hyperf\Snowflake\Concern\Snowflake;
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}
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```
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When the user model is created, the `Snowflake` algorithm will be used to generate the primary key by default.
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