What causes the MyBatis-Plus query results to be inconsistent?

Analysis of the problem of inconsistent query results caused by MyBatis-Plus cache

This article analyzes a problem of inconsistency in the previous and subsequent search results of MyBatis-Plus. Problem phenomenon: After last value of the database field is updated, the first query reads the new value, but the second query reads the old value, and then the latest value is read again.

The log displays key information:

1. First query (17:49:09.423): last value is 22, then updated to 23, and read immediately to last = 23 .
2. Second query (17:50:00.010): last value falls back to 22 abnormally.
3. The third query (17:50:00.012): last value correctly reads the latest value 1048.

This phenomenon is likely caused by MyBatis-Plus' caching mechanism. MyBatis-Plus uses Level 1 cache (SqlSession level) and Level 2 cache (Mapper level) by default.

If a secondary cache is used and the cache invalidation strategy is inappropriate, the second query may read the old data from the cache rather than the latest data in the database after updating the data. This explains why the second query result is last = 22 even if last value has been updated multiple times and reaches 1048. After that, the cache is invalid or cleared, and the latest data is read only after the third query.

The database transaction isolation level can also cause problems, but the log shows that the two query intervals indicate that the first transaction has been committed, so the probability of this factor is less.

Solution:

It is recommended to check the MyBatis-Plus cache configuration and consider the following scenarios:

• Turn off Level 2 cache: This is the most direct solution, which can effectively avoid data inconsistencies caused by cache.
• Adjust cache failure strategy: If you need to retain the secondary cache, you need to adjust the cache failure strategy, such as shortening the cache validity time or using a more appropriate failure strategy.
• Check concurrency issues: Troubleshoot whether there are concurrent access to the database in the code, such as multiple threads updating the same data at the same time.

If the above method still fails to solve the problem, you need to further check the database transaction isolation level settings and other potential issues in the code.

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