The document discusses steps for troubleshooting MySQL issues: (1) define the problem precisely, (2) collect diagnostic data from the operating system and MySQL, and (3) examine the error log. It then provides guidance on diagnosing specific issues like crashes, performance problems, table corruption, and replication errors.

1. Copyright © 2017, Oracle and/or its affiliates. All rights reserved. |
MySQL Troubleshooting
TL;DR
Ligaya Turmelle
Principal Technical Support Engineer - MySQL
ligaya.turmelle@oracle.com
@lig
rootconf - May 2017

2. Copyright © 2017, Oracle and/or its affiliates. All rights reserved. |
MySQL Troubleshooting
TL;DR
Ligaya Turmelle
Principal Technical Support Engineer - MySQL
ligaya.turmelle@oracle.com
@lig
rootconf - May 2017

3. Copyright © 2017, Oracle and/or its affiliates. All rights reserved. |
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Step 1
• Define the problem
• Must know what is “normal”, to know what is not “normal” - and how
much
• Be exact!
• Read and understand the manual for the problematic area
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Step 2
• Collect the diagnostic data
– OS data
– MySQL data
• May need to collect the diagnostic data during the problem
– Monitoring
– Maybe pt_stalk
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Error Log
• First place to look
• Can give history and context to any problem
• Error message(s)
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General Server Crash
• Error log
– Stack trace and error message(s)
• OS error log around the crash time
– OOM
• Any and all diagnostic data available
– MySQL and OS monitoring data (graphs and raw data)
– Core file?
• Any information about what was happening before and during the crash
– External scripts running / Applications / Cronjobs / Backups / Etc.
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General Performance Issues
• Error log
• COS data (Ex: IO, CPU, Memory, NUMA, etc.)
• SHOW GLOBAL VARIABLES
• SHOW GLOBAL STATUS
• SHOW FULL PROCESSLIST
• SHOW ENGINE INNODB STATUS
• Information from PERFORMANCE_SCHEMA
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Query Performance Issues
• Error log
• Slow query log
• EXPLAIN
• SHOW CREATE TABLE
• SHOW TABLE STATUS
• SHOW INDEXES
• Profile the query
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Table Corruption
• InnoDB
– System may or may not be able to start back up
– Error log
• Error message
• Stack trace
– Known issue?
• Bug
• Data dictionary issues
– Rebuild
• Go to a backup
• Force recovery
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Table Corruption
• MyISAM
– Error log
– Marked as crashed?
– myisamchk or mysqlcheck
• Server up or down?
• Backup corrupted files before - some data loss can happen
– Backups are always an option
(con’t)
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Replication Issues
• Error log
• SHOW MASTER STATUS
• my.cnf / my.ini
• SHOW GLOBAL VARIABLES
• SHOW SLAVE STATUS
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13. Copyright © 2017, Oracle and/or its affiliates. All rights reserved. |
MySQL Troubleshooting
TL;DR
Ligaya Turmelle
Principal Technical Support Engineer - MySQL
ligaya.turmelle@oracle.com
@lig
rootconf - May 2017