How to Optimize Queries in MariaDB

How do I optimize slow queries in MariaDB?

Optimizing queries in MariaDB means analyzing execution plans, adding proper indexes, and rewriting SQL so each statement returns the same result with fewer reads, writes, and CPU cycles.

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Description

Example H2

Example H3

Why should I optimize MariaDB queries?

Slow queries block connections, waste CPU, and delay user-facing features. Tuning them lowers latency, cuts infrastructure costs, and leaves head-room for traffic spikes.

What tools identify slow MariaDB queries?

Turn on the slow query log, then run EXPLAIN or ANALYZE on candidates. These commands reveal join order, key usage, and estimated rows.

How do I read an EXPLAIN plan?

Focus on type, rows, and extra. A type value of ALL means a full scan; aim for ref or const. Large rows counts signal missing indexes.

Which EXPLAIN columns matter most?

possible_keys shows usable indexes. key lists the one actually picked. filtered reveals how many rows survive the condition.

Which indexes boost performance?

Create composite b-tree indexes that match filter columns in order. Use covering indexes to satisfy SELECT lists without extra lookups.

How do I add the right index?

Index columns that appear in JOIN, WHERE, and ORDER BY clauses. Avoid over-indexing; each write must update every extra index.

How can I rewrite queries for speed?

Replace SELECT * with needed columns, avoid functions on indexed columns, and break huge IN lists into temp tables.

When should I use optimizer hints?

Add /*+ INDEX(Orders order_date) */ or STRAIGHT_JOIN when the optimizer’s default plan is sub-optimal. Test both before and after.

Best practices checklist

1) Profile with ANALYZE FORMAT=JSON. 2) Add or adjust indexes. 3) Keep statistics fresh with ANALYZE TABLE. 4) Limit result sets with pagination.

Why How to Optimize Queries in MariaDB is important

How to Optimize Queries in MariaDB Example Usage


-- Identify slow Orders for a single customer in 2023
EXPLAIN ANALYZE SELECT o.id, SUM(oi.quantity * p.price) AS spend
FROM Orders o
JOIN OrderItems oi ON oi.order_id = o.id
JOIN Products p   ON p.id = oi.product_id
WHERE o.customer_id = 42
  AND o.order_date BETWEEN '2023-01-01' AND '2023-12-31'
GROUP BY o.id;

How to Optimize Queries in MariaDB Syntax


-- Inspect a query plan
EXPLAIN [ANALYZE] [FORMAT=JSON] SELECT columns
FROM Orders o
JOIN Customers c ON c.id = o.customer_id
WHERE o.order_date >= '2023-01-01';

-- Create a composite index for a common filter
CREATE INDEX idx_orders_customer_date
  ON Orders (customer_id, order_date);

-- Use an optimizer hint when needed
SELECT /*+ INDEX(o idx_orders_customer_date) */
       o.id, o.total_amount
FROM Orders o
WHERE o.customer_id = 5
  AND o.order_date >= '2023-06-01';

Common Mistakes

Not checking the slow query log first. Guessing which query is slow wastes time. Enable <code>slow_query_log</code>, set a low <code>long_query_time</code>, and target the worst offenders.
Creating single-column indexes for every filter. Over-indexing slows INSERT/UPDATE. Use composite indexes that match the most selective columns in order.