Hi Catal

From experience, in most cases where a mariadb server uses more memory than expected, especially if it’s consistently growing to the point of oomkiller taking it out, the culprit has been the default malloc handler on the OS. I’ve found this both on various flavours of EL (Centos and Rocky, 6-9) as well as Debian 12.

As it’s a bit of a FAQ, I jotted down how we solve it by using jemalloc or tcmalloc, both of which work well with MariaDb on linux.

https://digdilem.org/2025/03/solving-excess-memory-usage-in-mariadb/

I would suggest trying that before going further. It’s a quick and cheap fix, and if it doesn’t work, easy to revert.

Regards, Simon

See below:
Operating system: "Debian 12.10 (bookworm)"

MariaDB Version: 10.11.11-MariaDB-0+deb12u1-log

The server was configured (limited) to use for InnoDB -> max 3GB Ram

But, on that server we are running also MySam, Memory and Innodb, in total, ~70 databases (8 MySam, 1 MEMORY, and the rest are InnoDB)

MariaDB [mysql]> select count(distinct db) from db;
+--------------------+
| count(distinct db) |
+--------------------+
| 73 |
+--------------------+
1 row in set (0.001 sec)
MariaDB [mysql]>

SYSTEM 4CPU, 7.8GB RAM

root@adsns-db-node0:~# df -h
Filesystem Size Used Avail Use% Mounted on
udev 3.8G 0 3.8G 0% /dev
tmpfs 776M 764K 775M 1% /run
/dev/sda1 150G 48G 97G 34% /
tmpfs 3.8G 0 3.8G 0% /dev/shm
tmpfs 5.0M 0 5.0M 0% /run/lock
/dev/sda15 241M 138K 241M 1% /boot/efi
tmpfs 776M 0 776M 0% /run/user/0
root@adsns-db-node0:~#

I found some articles on internet regarding /dev/shm, which could influence mysql performance.

In my case /dev/shm is not used even defined, so the system could use the whole available RAM - 7.8GB RAM, so I excluded this as possible cause.

MariaDB [(none)]> SHOW VARIABLES LIKE '%buffer_size%';
+----------------------------+-----------+
| Variable_name | Value |
+----------------------------+-----------+
| aria_pagecache_buffer_size | 134217728 |
| aria_sort_buffer_size | 268434432 |
| bulk_insert_buffer_size | 8388608 |
| innodb_log_buffer_size | 16777216 |
| innodb_sort_buffer_size | 1048576 |
| join_buffer_size | 4194304 |
| key_buffer_size | 10485760 |
| mrr_buffer_size | 262144 |
| myisam_sort_buffer_size | 134216704 |
| preload_buffer_size | 32768 |
| read_buffer_size | 131072 |
| read_rnd_buffer_size | 262144 |
| sort_buffer_size | 2097152 |
+----------------------------+-----------+
13 rows in set (0.001 sec)

Traffic is not high, just 123 queries per second.

MariaDB [(none)]> status;
--------------
mysql Ver 15.1 Distrib 10.11.11-MariaDB, for debian-linux-gnu (x86_64) using EditLine wrapper

Connection id: 877596
Current database:
Current user: root@localhost
SSL: Not in use
Current pager: stdout
Using outfile: ''
Using delimiter: ;
Server: MariaDB
Server version: 10.11.11-MariaDB-0+deb12u1-log Debian 12
Protocol version: 10
Connection: Localhost via UNIX socket
Server characterset: utf8mb4
Db characterset: utf8mb4
Client characterset: utf8mb3
Conn. characterset: utf8mb3
UNIX socket: /run/mysqld/mysqld.sock
Uptime: 7 days 3 hours 24 min 6 sec

Threads: 78 Questions: 75901186 Slow queries: 4891595 Opens: 12573592 Open tables: 2000 Queries per second avg: 123.007
--------------

MariaDB [(none)]>

Even I am restarting mariadb, after a short time, the memory usage is 85%

root@adsns-db-node0:~# free -g
total used free shared buff/cache available
Mem: 7 6 0 0 0 1
Swap: 0 0 0
root@adsns-db-node0:~#

The swap is not used, just the memory, which is ok.

CPU usage is less than ~10%, so is ok.

See below, output of top.

%Cpu(s): 2.2 us, 0.7 sy, 0.0 ni, 96.2 id, 0.4 wa, 0.0 hi, 0.4 si, 0.0 st
MiB Mem : 7750.8 total, 161.4 free, 6351.8 used, 712.6 buff/cache
MiB Swap: 0.0 total, 0.0 free, 0.0 used. 1399.0 avail Mem

PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
1555028 mysql 20 0 7752424 6.5g 15476 S 10.6 85.2 188:29.16 mariadbd

root@adsns-db-node0:~# pstree |grep maria
|-mariadbd---51*[{mariadbd}]
root@adsns-db-node0:~#

All 51 childs of mariadb are using 85% from the system memory (each child ~1.6% of total RAM).

I found a mysql calculator and changing innodb_buffer_pool_size - its default value 8M - with 3G, I got ~3.7GB ... still not 6.6G (aprox 85% from total RAM).

See: https://www.mysqlcalculator.com/

5. Why this difference, from 3.7GB up to 6.6GB?

6. Where could it be the rest of 2GB which is used by mariadb (from 3.7GB up to 6.6GB)?

Any help will be appreciated.

Catal

From: cata via discuss <discuss@lists.mariadb.org>
Sent: 02 April 2025 15:27
To: discuss@lists.mariadb.org
Subject: [MariaDB discuss] it is normal to have a memory usage of 85%?

Hi everybody,

I am new here and I am confronted with a situation, so I will start with the questions first:

1. It is normal that on my server, mariadb to use almost 85% of available ram or something is wrong?

2. In case I want to limit the whole application (mariadb) to not use more than 5.5 GB RAM from total of 7.8GB it could be possible - without affecting it's performance?

3. Is anything to optimize (change) now? If yes, which variable?

4. Do we need more RAM for this server or actual RAM could be enough?