Linear Trees in InnoDB
Tags: innodb, mysql
Published: 2024-01-27 05:15:47

In InnoDB, a linear tree is a type of data structure used for indexing and searching data. Linear trees are also known as B+ trees. The key characteristic of a linear tree is that all the data is stored in a sorted order, with a pointer to the next leaf node. This allows for efficient searching and insertion of data.

InnoDB  uses a modified version of linear tree called a "compressed" B+ tree. Each node of the tree contains multiple keys, and the keys are stored in a sorted order. The keys are used to determine the path that a query should take when searching for data. When a node is full, it is split into two nodes, with the middle key moving up to the parent node. This helps to keep the tree balanced and ensures that the search time is always logarithmic.

InnoDB uses linear trees to store the primary key and secondary indexes of a table. Each leaf node of the tree contains the actual data rows of the table. When a query is executed, the optimizer uses the keys stored in the tree to determine the most efficient path to the data. This allows InnoDB to quickly locate and retrieve the requested data.

Linear trees are commonly used in relational databases and other systems that need to store and retrieve large amounts of data efficiently. The use of linear tree in InnoDB provides many benefits, such as fast search and insertion, support for concurrent operations, and the ability to handle large amounts of data.


**Python code to monitor unused and redundant indexes in InnoDB**




In MySQL, you can use the MySQL Performance Schema to monitor the usage of indexes and detect unused or redundant indexes. The Performance Schema provides several tables that allow you to track the usage of indexes, including the table performance_schema.table_io_waits_summary_by_index_usage

Here is an example of how you can use the Performance Schema to monitor the usage of indexes in InnoDB using the mysql-connector-python library:

```
import mysql.connector

# Connect to the MySQL server
cnx = mysql.connector.connect(user='<username>',
                              password='<password>',
                              host='<hostname>',
                              database='<database>')

# Create a cursor object
cursor = cnx.cursor()

# Execute a query to retrieve information about index usage
cursor.execute("""
    SELECT object_schema, object_name, index_name, SUM(count_fetch) as fetch_count, SUM(count_scan) as scan_count
    FROM performance_schema.table_io_waits_summary_by_index_usage
    WHERE object_schema NOT IN ('performance_schema', 'sys')
    GROUP BY object_schema, object_name, index_name
    ORDER BY fetch_count, scan_count;
""")

# Fetch the results
results = cursor.fetchall()

# Print the index usage information
for row in results:
    print("Schema: ", row[0])
    print("Table: ", row[1])
    print("Index: ", row[2])
    print("Fetch Count: ", row[3])
    print("Scan Count: ", row[4])
    print("\n")

# Close the cursor and the connection
cursor.close()
cnx.close()
```

This code creates a connection to the MySQL server using the mysql-connector-python library, creates a cursor object, and then executes a query to retrieve information about index usage from the performance_schema.table_io_waits_summary_by_index_usage table. The query groups the results by the schema, table, and index name and calculates the total number of fetches and scans for each index. The results are then fetched and printed.

You can use the results of this query to determine which indexes are not being used and may be redundant. For example, if an index has a low fetch count and a low scan count, it may not be needed and can be removed.

It's worth noting that this is an example of how you can monitor index usage, and you should adjust the query to match your specific requirements. Also, it's important to test any changes to indexes in a development environment before applying them to a production environment.

Read more InnoDB blogs here:

- [Enhancing Write Performance: Key Strategies for Optimizing the InnoDB Buffer Pool in MySQL](https://minervadb.xyz/enhancing-write-performance-key-strategies-for-optimizing-the-innodb-buffer-pool-in-mysql/)

- [Optimizing InnoDB for Peak Performance: A Deep Dive into Seek/Scan Costs and Statistics Management](https://minervadb.xyz/optimizing-innodb-for-peak-performance-a-deep-dive-into-seek-scan-costs-and-statistics-management/)

- [Troubleshooting InnoDB Buffer Pool Eviction Issues](https://minervadb.xyz/troubleshooting-innodb-buffer-pool-eviction-issues/)
- [Advanced InnoDB Performance Monitoring: Using Statistics and Forecasts for Optimization](https://minervadb.xyz/advanced-innodb-performance-monitoring-using-statistics-and-forecasts-for-optimization/)

- [InnoDB Performance Optimization: Key System Variables and Recommended Settings](https://minervadb.xyz/innodb-performance-optimization-key-system-variables-and-recommended-settings/)