How to Check Memory Usage in MySQL

Galaxy Glossary

How do I check MySQL memory usage with SQL commands?

Use SHOW commands and performance_schema views to inspect server-wide and per-component memory allocations in MySQL.

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Description

Why track MySQL memory usage?

Staying under available RAM prevents swapping, keeps queries fast, and avoids server crashes. Continuous visibility lets you resize buffers and tune queries early.

How do I view global buffer sizes fast?

Issue SHOW VARIABLES LIKE '%buffer%size'; to list all core caches. Focus on innodb_buffer_pool_size, key_buffer_size, and query_cache_size.

How can I get live allocation totals?

performance_schema.memory_summary_global_by_event_name reports current bytes allocated per engine component. Sort by current_alloc to locate the biggest consumers.

SQL example

SELECT event_name, current_alloc/1024/1024 AS mbFROM performance_schema.memory_summary_global_by_event_nameORDER BY current_alloc DESCLIMIT 10;

Which session is eating RAM?

Combine performance_schema and information_schema.processlist to see per-thread memory. Join on THREAD_ID and ID for precise attribution.

Can I monitor memory while querying ecommerce data?

Yes. Wrap business queries—like retrieving customer order totals—in performance_schema.setup_instruments to capture their memory footprint without altering application logic.

Best practices

Enable performance_schema at startup, export metrics to Prometheus, and set warning thresholds. Resize buffers gradually and test under load.

Common pitfalls

Relying only on OS tools hides internal fragmentation. Forgetting to divide bytes into MB leads to misinterpretation of numbers.

Why How to Check Memory Usage in MySQL is important

How to Check Memory Usage in MySQL Example Usage


SELECT c.id, c.name, SUM(o.total_amount) AS lifetime_value
FROM Customers c
JOIN Orders   o ON o.customer_id = c.id
GROUP BY c.id, c.name
ORDER BY lifetime_value DESC
LIMIT 5;
-- Immediately check how much memory this session allocated
SELECT event_name, current_alloc/1024 AS kb
FROM performance_schema.memory_summary_by_thread_by_event_name
WHERE thread_id = (SELECT THREAD_ID
                   FROM performance_schema.threads
                   WHERE PROCESSLIST_ID = CONNECTION_ID())
ORDER BY current_alloc DESC;

How to Check Memory Usage in MySQL Syntax


-- Show all buffer-related variables
SHOW VARIABLES LIKE '%buffer%size';

-- Examine specific global caches
SHOW VARIABLES LIKE 'innodb_buffer_pool_size';
SHOW VARIABLES LIKE 'key_buffer_size';

-- Detail current allocations per memory event
SELECT event_name,
       current_alloc   AS bytes_in_use,
       high_alloc      AS peak_bytes
FROM performance_schema.memory_summary_global_by_event_name
WHERE event_name LIKE 'memory/innodb/%'
ORDER BY current_alloc DESC
LIMIT 10;

-- Correlate memory to a running ecommerce query
-- Assume session returns top spenders from Orders table
SET @thread_id = (SELECT THREAD_ID FROM performance_schema.threads
                  WHERE PROCESSLIST_ID = CONNECTION_ID());

/* run your SELECT customer_id, SUM(total_amount) ... */

SELECT *
FROM performance_schema.memory_summary_by_thread_by_event_name
WHERE thread_id = @thread_id
ORDER BY current_alloc DESC;

Common Mistakes

Only viewing OS-level RAM. This misses MySQL internal fragmentation and per-component stats. Fix: query performance_schema for precise allocations.
Reading bytes as kilobytes or megabytes, leading to wrong conclusions. Fix: convert with /1024 or format_bytes() before analysis.

Frequently Asked Questions (FAQs)

Does enabling performance_schema slow MySQL?

Overhead is usually <5 %, especially when you leave optional consumers disabled. The insight gained outweighs the minor cost.

Which version supports memory_summary_global_by_event_name?

MySQL 8.0 and MariaDB 10.5+ include this view. Older versions require INFORMATION_SCHEMA.INNODB_SYS_MEMORY, or upgrade.

Can I set hard memory limits per user?

Yes. Use max_user_connections and MEMORY resource group controls, or run queries inside containers with cgroup limits.

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