existMySQLmiddle,SQL QueryThe execution involves multiple memory areas and processing steps to ensure that queries can be executed efficiently and return results. The following is the memory path that SQL queries usually pass when executed in MySQL:
1. Client memory
- SQL text sending : SQL query is first sent from the client to the MySQL server. Client memory is used to store and send SQL query text.
2. Network buffer
- Receive and process requests : SQL queries are transmitted to the MySQL server over the network, enter the network buffer (Network Buffer) on the server side, and wait for processing.
3. Parser and Optimizer Memory
-SQL parsing : The MySQL parser parses the SQL query into a syntax tree. This process uses parser memory to store the intermediateData structure。
- Query Optimization : The MySQL optimizer generates multiple query execution plans and selects the optimal execution path. This process uses optimizer memory to calculate and store information about the execution plan.
4. Query cache (optional)
- Query cache checking : MySQL checks whether there are already results in the query cache (if the query cache is enabled). If the query result is cached and not expired, it will be directly from the query cacheReturn result, thereby skipping subsequent processing steps.
5. Table Cache
- Table opening and management : If the table involved in the query is not opened, MySQL will check in the table cache and try to open the table file. Table cache memory is used to store metadata and file handles for open tables.
6. Memory Tables
-Memory Temporary Table : Some complex queries, such as queries with `GROUP BY`, `ORDER BY`, or `DISTINCT`, may require MySQL to create temporary tables in memory to store intermediate results. If the data volume is too large, temporary tables may be stored to disk.
Buffer Pool
-Data page cache : MySQL uses InnoDB buffer pool to cache table data and index pages. The table data involved in the query process is first searched in the buffer pool. If it is missed, the corresponding data page is loaded from the disk to the buffer pool.
- Index and Data Access : Buffer pool is used to store frequently accessed index and table data to reduce disk I/O operations and improve query speed.
8. Sort Buffer
-Sorting Operations : If the query contains a sort operation (`ORDER BY`), MySQL may use a sort buffer to store the data that needs to be sorted. This buffer size can be adjusted by configuration parameters.
9. Join Buffer
-Table Join Operation : When dealing with multi-table joins (especially nested loop joins), MySQL may use a connection buffer to store intermediate results.
10. Server memory
-Execution query plan : Finally, MySQL performs query execution based on the execution plan generated by the optimizer. During the execution process, data is read from disk into memory for processing and operated through different memory areas (such as buffer pools, sorting buffers, connection buffers, etc.).
11. Result set generation
- Generate final result : After the query is executed, generate the result set and put it into the result cache for sending it back to the client.
12. Network Buffer
-Send result set : The result set is sent back to the client through the network buffer on the server side.
13. Client memory
-Receive and display results : Finally, the client receives the query results and stores and processes this data in the client memory.
Summarize
MySQL query execution involves multiple memory areas, from parsing and optimizing queries to processing data and generating results, each step is completed in a specific memory area. This memory path design is designed to maximize query execution efficiency and minimize disk I/O to improveperformance。