What is the purpose of fetchsize in MyBatis?

In MyBatis, the fetchSize refers to the number of records retrieved from the database at once. Its purpose is to control the number of rows the JDBC driver retrieves from the database. By setting an appropriate fetchSize value, it can reduce the number of database queries and improve data retrieval efficiency.

By default, the JDBC driver loads all query results into memory at once and then returns them to the application. This is fine for small data sets, but for large data sets, it can consume a lot of memory and potentially lead to a memory overflow.

By setting the fetchSize, you can instruct the JDBC driver on how many records to fetch from the database each time. This allows for loading records into memory in batches when dealing with large query results, reducing memory consumption. Additionally, setting an appropriate fetchSize value can improve data retrieval efficiency, reduce database query frequency, and ultimately enhance system performance.

It is important to note that the fetchSize setting is not about setting it as large as possible, but about determining the appropriate value based on specific business requirements and system environment. A fetchSize value that is too small will result in frequent network transfers, increasing query time overhead; whereas a fetchSize value that is too large may consume too much memory. Therefore, adjustments and optimizations should be made according to the actual circumstances.