How to Check Memory Usage in MariaDB

How do I check memory usage in MariaDB?

Use SHOW STATUS, SHOW VARIABLES, and PERFORMANCE_SCHEMA queries to inspect MariaDB memory consumption per buffer, thread, and engine.

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Description

Example H2

Example H3

Why monitor memory usage in MariaDB?

MariaDB keeps data in caches, buffers, and per-connection areas. Exceeding RAM limits causes swapping and slow queries. Regular checks help tune buffers and spot leaks.

How do I enable memory instrumentation?

Start the server with performance_schema=ON and performance-schema-instrument='memory/%=ON'. These flags activate the memory_% summary tables.

What SHOW commands reveal memory usage?

SHOW GLOBAL STATUS LIKE 'Innodb_buffer_pool%'; shows total buffer-pool memory. SHOW VARIABLES LIKE 'max_connections'; helps estimate per-thread memory.

How do PERFORMANCE_SCHEMA views help?

memory_summary_global_by_event_name lists every internal allocator, its current byte count, and the high-water mark. Sorting by CURRENT_NUMBER_OF_BYTES_USED highlights large consumers.

Which parameters control memory?

innodb_buffer_pool_size, query_cache_size, tmp_table_size, and max_connections are the main tunables. Align totals with available RAM minus OS overhead.

Example: find top memory consumers in an ecommerce database

The query below lists the five allocations that currently occupy the most RAM.

SELECT EVENT_NAME, CURRENT_NUMBER_OF_BYTES_USED/1024/1024 AS mb_used, HIGH_NUMBER_OF_BYTES_USED/1024/1024 AS mb_high FROM performance_schema.memory_summary_global_by_event_name ORDER BY CURRENT_NUMBER_OF_BYTES_USED DESC LIMIT 5;

How to calculate expected memory usage?

Multiply max_connections by estimated per-thread buffers (≈4–6 MB) and add global caches such as innodb_buffer_pool_size. Keep the sum below 80 % of total RAM.

Best practices

1) Enable performance_schema in staging first. 2) Graph key metrics—buffer pool, temp tables, and sort buffers—in Prometheus or Grafana. 3) Review after major workload or schema changes.

Common mistakes and fixes

Mistake 1 – Ignoring per-connection buffers. Even with a small buffer pool, hundreds of connections can exhaust RAM. Lower max_connections or use pooling.

Mistake 2 – Sampling only at startup. Memory grows with traffic. Schedule queries every minute and alert on spikes.

Additional resources

MariaDB docs: Performance Schema Memory, Server Status Variables.

Why How to Check Memory Usage in MariaDB is important

How to Check Memory Usage in MariaDB Example Usage


-- Find memory used by temp tables created while joining Orders and OrderItems
SELECT EVENT_NAME,
       CURRENT_NUMBER_OF_BYTES_USED/1024/1024 AS mb_used
FROM performance_schema.memory_summary_global_by_event_name
WHERE EVENT_NAME LIKE 'memory/temptable/%'
ORDER BY mb_used DESC
LIMIT 3;

How to Check Memory Usage in MariaDB Syntax


SHOW GLOBAL STATUS LIKE 'Innodb_buffer_pool%';
SHOW VARIABLES LIKE 'max_connections';

-- Detailed view via performance_schema
SELECT EVENT_NAME,
       CURRENT_COUNT_USED,
       CURRENT_NUMBER_OF_BYTES_USED,
       HIGH_NUMBER_OF_BYTES_USED
FROM performance_schema.memory_summary_global_by_event_name
ORDER BY CURRENT_NUMBER_OF_BYTES_USED DESC;

-- Ecommerce context example
-- Suppose many "Orders" reports run simultaneously and create temp tables
SHOW STATUS LIKE 'Created_tmp_disk_tables';

Common Mistakes

Setting a huge innodb_buffer_pool_size without lowering max_connections. The sum can exceed RAM. Fix by balancing global and per-thread allocations.
Running SHOW STATUS once and assuming memory stays flat. Memory rises under load. Fix by continuous monitoring or scheduled queries.