Memory Table on FromDual GmbH

VSZ behaviour with MariaDB MEMORY tables

oli.sennhauser@fromdual.com (Oli Sennhauser) — Tue, 05 Jan 2021 17:08:57 +0000

We recently had the situation that a customer complained about the Oom killer terminating the MariaDB database instance from time to time. The MariaDB database configuration was sized quit OK (about 50% of RAM was used for the database) but they did not have swap configured.

MySQL tmpdir on RAM-disk

oli.sennhauser@fromdual.com (Oli Sennhauser) — Thu, 15 Nov 2012 19:15:49 +0000

MySQL temporary tables are created either in memory (as MEMORY tables) or on disk (as MyISAM tables). How many tables went to disk and how many tables went to memory you can find with:

Example 1

oli.sennhauser@fromdual.com (Oli Sennhauser) — Fri, 09 Dec 2011 10:07:51 +0000

CREATE TABLE `order` (
 id INT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY
, name VARCHAR(64) NOT NULL
) ENGINE = InnoDB;

INSERT INTO `order` VALUES
 (NULL, 'Test order 1')
, (NULL, 'Test order 2')
, (NULL, 'Test order 3');


CREATE TABLE pos (
 id INT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY
, order_id INT UNSIGNED NOT NULL
, name VARCHAR(64) NOT NULL
, amount SMALLINT NOT NULL
, price DECIMAL (6,2) NOT NULL
, status TINYINT NULL
) ENGINE = InnoDB;

INSERT INTO pos VALUES
 (null, 1, 'Schrauben', 50, 0.10, 0)
, (null, 1, 'Muttern', 50, 0.10, 0)
, (null, 2, 'Nägel', 1000, 0.05, 1);


CREATE TABLE pos_shadow LIKE pos;
ALTER TABLE pos_shadow ENGINE = MEMORY;
INSERT INTO pos_shadow SELECT * FROM pos;

delimiter //

CREATE TRIGGER upd BEFORE UPDATE ON pos
FOR EACH ROW
BEGIN
 UPDATE pos_shadow AS p
 JOIN `order` AS o ON o.id = p.order_id and o.id = NEW.order_id
 SET status = 1
 WHERE o.id = 1;
END;
//

delimiter ;

SELECT o.name, p.name, p.amount, p.price, (p.amount*p.price) AS total, p. status
 FROM `order` AS o
 JOIN pos_shadow AS p ON p.order_id = o.id
;

UPDATE pos AS p
 JOIN `order` AS o ON o.id = p.order_id AND o.id = 1
 SET p.status = 1, p.order_id = 1
 where o.id = 1;

SELECT o.name, p.name, p.amount, p.price, (p.amount*p.price) AS total, p. status
 FROM `order` AS o
 JOIN pos AS p on p.order_id = o.id
;

Transactional memory resident tables with PBXT

oli.sennhauser@fromdual.com (Oli Sennhauser) — Sun, 21 Nov 2010 21:32:18 +0000

Introduction

In his presentation about PBXT at the DOAG Conference 2010 Paul McCullagh was speaking about memory resident PBXT tables. They will be available in version 1.1 of the PBXT Storage Engine Plugin. Memory resident PBXT tables should have similar characteristics like normal MySQL MEMORY</span> tables</a>. But in addition to the MEMORY tables they are transactional and can handle BLOB</span> and TEXT attributes.

MySQL hints

oli.sennhauser@fromdual.com (Oli Sennhauser) — Mon, 15 Mar 2010 13:38:54 +0000

MySQL pluggable Storage Engines (SE)

oli.sennhauser@fromdual.com (Oli Sennhauser) — Thu, 11 Mar 2010 23:20:51 +0000

One of the big advantages of MySQL is its concept of Pluggable Storage Engines. This means you can choose the most optimal Storage Engine for your needs. This also has a disadvantage: You have to know what you are doing…