Does `SELECT *` Impact Database Performance?

*`SELECT ` Impact on database performance**

In database operations, it is a common question whether using SELECT * to get all columns versus specifying only the required columns in the query SELECT column affects performance. This article explores the potential impact of both approaches on I/O and memory usage.

Network overhead

Regarding network overhead, using SELECT * does result in additional data transfer if the query retrieves more columns than actually needed. This is because the database server needs to send all data in a given table to the network, even if some columns are not used.

I/O Performance

On the other hand, it is not always clear whether the database engine will fetch the entire tuple (row) from disk even if only a specific column is requested using SELECT column. In some cases, the engine may optimize a query by selectively reading only the necessary data. However, in many database systems, obtaining the entire tuple is the typical approach. Therefore, the I/O overhead is generally similar in both cases.

Memory consumption

When the database engine fetches the entire tuple, it needs to allocate memory to temporarily store it. By selecting only the required columns instead of *, the query reduces the memory consumption of storing unnecessary data. This is especially beneficial in complex queries involving large amounts of data.

Conclusion

While the I/O overhead of the two methods may be comparable, using SELECT column instead of SELECT * can significantly reduce network overhead and memory consumption. By specifying only necessary columns, developers can optimize database performance and avoid unnecessary resource utilization. Therefore, it is recommended to avoid using SELECT * in production code whenever possible to improve query efficiency.

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