Streaming versus blocking operators in MySQL

In MySQL, operators in a query execution plan can be classified as streaming or blocking based on how they process and propagate rows during query execution. Let’s explore the differences between streaming and blocking operators in MySQL:

  1. Streaming Operators:
    • Streaming operators process and propagate rows in a continuous, stream-like manner as they are produced.
    • They operate on one row at a time, consuming and producing rows as they go.
    • Examples of streaming operators in MySQL include filters (WHERE clause), projections (SELECT clause), and simple joins.
  2. Blocking Operators:
    • Blocking operators need to consume and buffer all rows from their input before they can produce any output.
    • They require materializing or buffering all rows in memory or temporary storage before processing them.
    • Blocking operators introduce a synchronization point in the query execution plan, which can impact performance and memory usage.
    • Examples of blocking operators in MySQL include sorting (ORDER BY), grouping (GROUP BY), and certain types of joins (e.g., hash joins).

Key Considerations:

  • Streaming operators generally provide better performance and memory efficiency because they process rows in a continuous manner without the need for buffering.
  • Blocking operators, on the other hand, introduce additional memory requirements and can impact query performance, especially when dealing with large datasets or complex queries.
  • The presence of blocking operators may indicate areas for potential optimization or performance tuning in a query execution plan.

Optimizing Queries:

  • It’s often beneficial to minimize the use of blocking operators or rearrange the query structure to reduce the impact of blocking operations.
  • Techniques such as using appropriate indexes, optimizing join conditions, and rewriting queries can help to avoid or mitigate the need for blocking operators.
  • Proper indexing and query design can enable more efficient streaming operations and reduce the need for costly blocking operations.

Query Execution Plan:

  • Analyzing the query execution plan (using EXPLAIN or EXPLAIN ANALYZE) can provide insights into the presence and impact of blocking and streaming operators.
  • Understanding the operators involved and their order of execution can help identify potential bottlenecks or areas for optimization.

Overall, optimizing the use of streaming and blocking operators is crucial for query performance in MySQL. By minimizing the use of blocking operators, optimizing queries, and understanding the implications of the operators in the execution plan, you can improve query performance and resource utilization in your MySQL database.

About Shiv Iyer 455 Articles
Open Source Database Systems Engineer with a deep understanding of Optimizer Internals, Performance Engineering, Scalability and Data SRE. Shiv currently is the Founder, Investor, Board Member and CEO of multiple Database Systems Infrastructure Operations companies in the Transaction Processing Computing and ColumnStores ecosystem. He is also a frequent speaker in open source software conferences globally.