Primary Key on FromDual GmbH

Learning from the Bugs Database

oli.sennhauser@fromdual.com (Oli Sennhauser) — Thu, 20 Jan 2022 15:05:52 +0000

This week I came across an old known issue reported in May 2010: Master/Slave Replication with binlog_format = ROW and tables without a Primary Key is a bad idea! Especially if these tables are huge.

How the Lack of a Primary Key May Effectively Stop the Slave

oli.sennhauser@fromdual.com (Oli Sennhauser) — Tue, 02 May 2017 09:50:52 +0000

Most (relational) DBAs and DB application developers know the concept of a primary key (“PK”) and what it is good for. However, much too often one still encounters table definitions without a PK. True, the relational theory based on sets does not need a PK, and all operations (insert, select, update, delete) can also be done on tables for which no PK was defined. If performance doesn’t matter (or the data volume is small, a typical situation in tests), the lack of a PK does not immediately cause negative consequences.

Deadlocks, indexing and Primary Key's

oli.sennhauser@fromdual.com (Oli Sennhauser) — Thu, 16 Aug 2012 10:51:40 +0000

Recently a customer has shown up with some deadlocks occurring frequently. They were of the following type (I have shortened the output a bit):

Canias optimizations

oli.sennhauser@fromdual.com (Oli Sennhauser) — Wed, 28 Dec 2011 16:02:23 +0000

Canias is a great ERP product but there is still some potential to improve it. We only focus on MyISAM/InnoDB installations of Canias v6.0.2 in this article. For other DB back-ends those recommendations might be obsolete.

Disadvantages of explicitly NOT using InnoDB Primary Keys?

oli.sennhauser@fromdual.com (Oli Sennhauser) — Mon, 20 Sep 2010 15:36:36 +0000

We recently had the case with one of our customers where we got externally generated random hash values (up to 70 bytes) and they were used as Primary Keys in InnoDB.

MySQL hints

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

MariaDB and MySQL PERFORMANCE_SCHEMA Hints

oli.sennhauser@fromdual.com (Oli Sennhauser) — Sun, 14 Jul 2013 09:29:09 +0200

Accounts not properly closing connections
Unused indexes
Who created temporary (disk) tables
Accounts which never connected since last start-up
Users which never connected since last start-up
Totally unused accounts (never connected since last restart and not used to check Stored Program or View privileges) since last start-up
SHOW FULL PROCESSLIST
Storage Engines per schema
Tables without a Primary Key
Bad SQL queries of users
SHOW PROFILE in PERFORMANCE_SCHEMA
SELECT, INSERT, UPDATE and DELETE per table
Top long running queries
Tables never written to
DML, DDL and DCL per account
Finding syntactically wrong/erroneous MySQL queries
Finding queries served by MySQL Query Cache
Grant access to sys schema to another user
Grant access to PERFORMANCE_SCHEMA schema to another user
Find InnoDB Locks
Find Metadata Locks
What did a Connection before sleeping?
How many statements did another (sleeping) connection?
MyISAM locking
Connections per user
Connections per user and IP
Accounts which could not connect or with connection errors
Temporary tables filling my disk
Who is writing to the binary log
Average binlog transaction size
Result size of SELECT statement
Find open long running transactions

MariaDB

On MariaDB you have to enable the Performance Schema first before use: