When and Why Should I Use Composite Indexes for Database Optimization?

When and Why to Use Composite Indexes

Composite indexes, which combine multiple columns into a single index, offer performance optimizations for specific querying scenarios. Here are the key considerations:

When to Use Composite Indexes:

• Use composite indexes when your queries frequently filter or sort by multiple columns in a specific order.
• Composite indexes benefit left-most subsets of columns, i.e., queries that use the first columns listed in the index.

Why Use Composite Indexes:

• Improved performance: Composite indexes optimize queries by allowing the database engine to quickly retrieve data without scanning the entire table.
• Reduced I/O operations: By using a composite index, the database can directly access the relevant data blocks, minimizing disk read operations.

Performance Ramifications:

• Increased Storage Overhead: Composite indexes require more storage space than single-column indexes, as they hold data for multiple columns.
• Reduced Update Performance: Updates involving the indexed columns may be slower due to additional indexing operations required.
• Index Proliferation: Creating too many composite indexes can lead to excess indexes, which can reduce performance and make database maintenance more complex.

Example Scenario:

In your Homes table, a composite index on geolat and geolng would benefit queries that filter or sort by both coordinates together or by geolat alone. It would not provide significant performance improvements for queries filtering by geolng alone.

explain Command Analysis:

The EXPLAIN output for your query suggests that the database engine is using the display_status index to filter the homes table. However, it does not benefit from any indexes on the geolat and geolng columns when performing the range queries on these fields. Creating a composite index on geolat and geolng would improve the performance of those range queries.

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