Go zero micro Service Practice Series (VII. How to optimize such a high demand)

In the first two articles, we introduced various best practices for cache usage , First, we introduce the basic postures used by cache , How to use go-zero How to write the cache code in the automatically generated cache and logic code , Then I explained the penetration in the face of cache 、 breakdown 、 Solutions to common problems such as avalanches , Finally, it focuses on how to ensure cache consistency . Because caching is very important for high concurrency services , So we will continue to learn about caching in this article .

Local cache

When we encounter extreme hot data queries , At this time, local cache should be considered . The hotspot local cache is mainly deployed in the code of the application server , Used to block hotspot queries for Redis Equally distributed cache or database pressure .

In our mall , home page Banner There will be some advertising products or recommended products in the , The information of these commodities is entered and changed by the operation in the management background . The demand for these goods is very large , Even if it's Redis It's hard to carry , So here we can use local cache to optimize .

stay product Create a commodity operation table in the warehouse product_operation, For simplicity, keep only the necessary fields ,product_id To promote the goods of the operation id,status Is the status of the operating commodity ,status by 1 It will be on the home page Banner Show the product in .

CREATE TABLE `product_operation` (
  `id` bigint unsigned NOT NULL AUTO_INCREMENT,
  `product_id` bigint unsigned NOT NULL DEFAULT 0 COMMENT ' goods id',
  `status` int NOT NULL DEFAULT '1' COMMENT ' Operation commodity status  0- Offline  1- go online ',
  `create_time` datetime NOT NULL DEFAULT CURRENT_TIMESTAMP COMMENT ' Creation time ',
  `update_time` datetime NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP COMMENT ' Update time ',
  PRIMARY KEY (`id`),
  KEY `ix_update_time` (`update_time`)
) ENGINE=InnoDB  DEFAULT CHARSET=utf8mb4 COMMENT=' Commodity operation table ';

The implementation of local caching is relatively simple , We can use map To do it on your own , stay go-zero Of collection Provided in Cache To realize the function of local cache , Let's just use it , It is never a wise choice to build the wheel repeatedly ,localCacheExpire Expiration time for local cache ,Cache Provides Get and Set Method , Very simple to use

localCache, err := collection.NewCache(localCacheExpire)

First look up from the local cache , If it hits the cache, it returns . If the cache is not hit, you need to query the operating bit commodity from the database first id, Then aggregate the product information , Finally, it is pushed back into the local cache . The detailed code logic is as follows ：

func (l *OperationProductsLogic) OperationProducts(in *product.OperationProductsRequest) (*product.OperationProductsResponse, error) {
  opProducts, ok := l.svcCtx.LocalCache.Get(operationProductsKey)
  if ok {
    return &product.OperationProductsResponse{Products: opProducts.([]*product.ProductItem)}, nil
  }

  pos, err := l.svcCtx.OperationModel.OperationProducts(l.ctx, validStatus)
  if err != nil {
    return nil, err
  }
  var pids []int64
  for _, p := range pos {
    pids = append(pids, p.ProductId)
  }
  products, err := l.productListLogic.productsByIds(l.ctx, pids)
  if err != nil {
    return nil, err
  }
  var pItems []*product.ProductItem
  for _, p := range products {
    pItems = append(pItems, &product.ProductItem{
      ProductId: p.Id,
      Name:      p.Name,
    })
  }
  l.svcCtx.LocalCache.Set(operationProductsKey, pItems)
  return &product.OperationProductsResponse{Products: pItems}, nil
}

Use grpurl Debug tool request interface , First request cache miss after , Subsequent requests will hit the local cache , When the local cache expires, it will go back to the source again db Load data into local cache

~ grpcurl -plaintext -d '{}' 127.0.0.1:8081 product.Product.OperationProducts
{
  "products": [
    {
      "productId": "32",
      "name": " Electric fan 6"
    },
    {
      "productId": "31",
      "name": " Electric fan 5"
    },
    {
      "productId": "33",
      "name": " Electric fan 7"
    }
  ]
}

Be careful , Not all information is suitable for local caching , The characteristic of local cache is that the request volume is very high , At the same time, certain inconsistencies can be allowed in business , Because the local cache generally does not take the initiative to update , You need to wait until it expires and go back to the source db Update later . Therefore, in the business, it depends on the situation to see whether the local cache is required .

Automatically identify hotspot data

home page Banner Scenarios are configured by operators , That is, we can know the hot data that may be generated in advance , But in some cases, we can not predict in advance that data will become a hot spot . So we need to be able to identify these hot data adaptively and automatically , Then promote the data to the local cache .

We maintain a sliding window , For example, the sliding window is set to 10s, It's about statistics 10s What's inside key Accessed by high frequency , One sliding window corresponds to multiple Bucket, Every Bucket Corresponding to one in map,map Of key For commodities id,value The number of requests corresponding to the product . Then we can do it regularly ( such as 10s) To count all the current Buckets Medium key The data of , Then import the data into the big top heap , It's easy to get from the big top pile topK Of key, We can set a threshold , For example, a certain time in a sliding window key Visit frequency exceeds 500 Time , Just think the key As a hot spot key, So that the key Upgrade to local cache .

Cache usage tips

Here are some tips for caching

• key Try to make the naming easy to read , That is to say, you can see the name and know the meaning , The length should be as small as possible on the premise that it is easy to read , To reduce the occupation of resources , about value You can use int Try not to use string, For less than N Of value,redis Internal shared_object cache .
• stay redis Use hash In the case of key The split , The same hash key Will fall into the same redis node ,hash Too large will lead to uneven distribution of memory and requests , Consider right hash Split into small hash, Make the node memory uniform to avoid single node request hotspots .
• To avoid nonexistent data requests , Cause each request to be cached miss Directly into the database , Set the empty cache .
• When objects need to be stored in the cache , Serialization try to use protobuf, Minimize data size .
• When adding new data, ensure that the cache must exist before adding , Use Expire To determine whether the cache exists .
• The need to store daily login scenarios , have access to BITSET, To avoid a single BITSET Too big or hot , Can be done sharding.
• In the use of sorted set When , Avoid using zrange perhaps zrevrange Returns a collection that is too large , High complexity .
• Try to use when caching PIPELINE, But also pay attention to avoid too large a collection .
• Avoid oversized value.
• Try to set the expiration time for the cache .
• Use the full operation command with caution , such as Hash Type of HGETALL、Set Type of SMEMBERS etc. , These operations will affect Hash and Set Full scan of the underlying data structure , If there is a large amount of data , It will block Redis The main thread .
• To get the full data of a collection type, you can use SSCAN、HSCAN Wait for the command to return the data in the set in batches , Reduce blocking of main threads .
• Use with caution MONITOR command ,MONITOR The command will continuously write the monitored content to the output buffer , If there are many online commands , The output buffer will overflow soon , Would be right Redis Performance impact .
• The production environment is disabled KEYS、FLUSHALL、FLUSHDB Wait for the order .

Conclusion

This article introduces how to use local hotspot cache to deal with ultra-high requests , Hotspot cache is divided into known hotspot cache and unknown hotspot cache . Known hotspot caches are simple , Load from the database into memory in advance , Unknown hotspot cache we need to adaptively identify the hotspot data , Then upgrade the data of these hotspots to local cache . Finally, some tips for caching in actual production are introduced , Be flexible in the production environment and try to avoid problems .

I hope this article can help you , thank you .

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Share the principles and best practices of microservices , Explain the underlying principles of service governance , Take you to read it carefully go-zero Source code .go-zero It's an integrated engineering practice web and rpc frame , Designed to shorten the distance from demand to online . The official account is wrong in the know number. ： Wan Junfeng Kevin

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