PDO::fetchAll() vs. PDO::fetch() in a Loop: Which is Better for Large Result Sets?

PDO::fetchAll() vs. PDO::fetch() in a Loop for Large Result Sets

Introduction

When dealing with large result sets in PHP using PDO, developers often face the question: Should they use PDO::fetchAll() or PDO::fetch() in a loop? This article explores the performance difference between these two approaches.

Performance Comparison

As a general rule, PDO::fetchAll() tends to be faster than using PDO::fetch() in a loop for large result sets. This is because PDO::fetchAll() fetches all rows of the result set in one operation, while PDO::fetch() performs multiple database queries, one for each row.

Memory Consumption

However, it's important to consider that fetching the entire result set into an array (as done by fetchAll()) requires more memory. This can be a significant factor for very large result sets. In such cases, using PDO::fetch() in a loop may be more appropriate if memory usage is a concern.

Benchmark Results

To provide a more concrete comparison, the following benchmark was performed:

fetchAll : 0.35965991020203s, 100249408b
fetch : 0.39197015762329s, 440b

As observed, fetchAll() was slightly faster but consumed significantly more memory.

Conclusion

Whether to use PDO::fetchAll() or PDO::fetch() in a loop depends on the size of the result set and the available memory resources. For large result sets, fetchAll() is typically faster but requires more memory. For result sets that are smaller or where memory usage is a concern, PDO::fetch() in a loop may be a better choice.

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