Understand TiDB caching technology

TiDB is a distributed NewSQL database that can meet the high availability and high performance requirements of enterprise-level applications. Caching technology is an important part of TiDB and can effectively improve TiDB query performance. This article will discuss TiDB’s caching technology.

1. Introduction to TiDB cache
   TiDB cache mainly consists of two parts, one is the TiKV cache and the other is the TiDB Server cache. The main function of TiKV cache is to accelerate the query of a single TiKV instance, while the TiDB Server cache is used to accelerate the query of multiple TiKV instances. The combination of these two caches can greatly improve the performance of TiDB.
2. TiKV cache
   TiKV cache mainly uses RocksDB for data storage. When a TiDB query request arrives, TiDB Server first queries TiKV to see if there is a data cache. If it exists, the result will be returned directly; if it does not exist, TiKV's disk storage will be queried. If the query is successful, TiKV stores the results in the cache for the next query.

In addition, TiKV also provides an anti-shake mechanism. When a large number of writes occur to TiKV disk storage, the anti-shake mechanism will pause cache updates and wait for the writes to complete before continuing to update the cache. This mechanism can reduce the impact of hot writes on the cache and improve the stability and reliability of the cache.

3. TiDB Server cache
   TiDB Server cache is mainly implemented using the LRU strategy. When the query request reaches TiDB Server, if the query statement exists in the cache, the result will be returned directly; if it does not exist, TiKV needs to be queried to obtain the data. Query results can be cached in TiDB Server for the next use of the same query.

The size of the TiDB Server cache can be adjusted through the configuration file, and the default is 100MB. If there is insufficient cache space, data that has not been used recently will be gradually cleared. This LRU cache strategy can make the TiDB Server cache adapt to data changes and improve query efficiency.

4. Application scenarios of TiDB cache
   Cache technology can greatly improve the query efficiency of TiDB, especially for some scenarios with high frequency read requests and low data changes, TiDB cache can play a greater role role.

For example, the product information page of an e-commerce website is usually visited many times, but the information on the product page does not change frequently, so it is very suitable to use TiDB caching technology. This can shorten the query time to the millisecond level and improve the user experience.

5. Summary
   TiDB caching technology is an important part of TiDB and can optimize TiDB’s query performance to a certain extent. TiKV cache and TiDB Server cache can effectively improve query efficiency, especially in scenarios with high frequency read requests and low data changes. In actual applications, it needs to be configured and adjusted according to specific conditions to achieve the best query effect.

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