MySQL Administration The Mysql Data Directory

MySQL AdministrationThe Mysql Data Directory

Chapter 11

MySql Developer's Library. Paul Dubois, 4th Ed

Location of the Data Directory

• mysql> SHOW VARIABLES LIKE 'datadir';

MySql Dwvwloper's Library. Paul Dubois, 4th Ed

Structure of the Data Directory

• Windows filesystem:– Each database has a database directory located

under the data directory.– Tables, views, and triggers within a database

correspond to files in the database directory.


Structure of the Data Directory

• The server's process ID (PID) file. – On Start-up the server writes its process ID to this file so

that other programs can discover the value if they need to send signals to it.

• Status and log files that are generated by the server. – files about server's operation and are valuable for

administrators, especially when something goes wrong and you're trying to determine the cause of the problem.

• Server-related files, such as the DES key file or the server's SSL certificate and key files.


How the MySQL Server Provides Access to Data

• In a client/server setup, all databases under the data directory are managed by a single entity, the MySQL server mysqld.

• Client programs never manipulate data directly. • The server provides the sole point of contact

through which databases are accessed, acting as the intermediary between client programs and the data they want to use.





• When the server starts, it opens any logs that you request it to maintain

• To access data, a client program establishes a connection to the server, and then communicates requests as SQL statements to perform the desired operations such as creating a table, selecting rows, or updating rows.

• The server performs each operation and sends back the result to the client.

• The server is multi-threaded and can service multiple simultaneous client connections.

• Because update operations are performed one at a time, the server in effect serializes requests so that two clients can never change a given row at exactly the same time.



• The server does not have exclusive control of the data directory when:– When you run multiple servers on a single data

directory. • It's possible to start multiple servers and point them at the

same data directory• NOT RECOMMENDED• System must provide good file locking or the servers will not

cooperate properly. • You also risk having your logs become a source of confusion if

you have multiple servers writing to them at the same time.



• When you use direct-access maintenance utilities.– Programs such as myisamchk and myisampack are used for MyISAM table

maintenance, troubleshooting, repair, and compression operations. – These programs operate directly on the files that correspond to the tables. – Because these utilities can change table contents, using them to operate

on tables at the same time the server is doing so can cause table damage.– Stop the server before running these table utilities. – If that is not possible, it's very important to understand how to tell the

server not to access a table while you're using a utility that operates directly on the table files

– An alternative to myisamchk is to use statements such as CHECK TABLE and REPAIR TABLE

• Eliminate the problem of interaction with the server by instructing the server itself to perform the table maintenance operations.


MySql Status and Log Files


The Process ID File

• The MySQL server writes its process ID (PID) into the PID file when it starts, and removes the file when it shuts down.

• Other processes can use this file to determine whether the server is running and what its process ID is if so.


The MySQL Logs

• MySQL can maintain several types of log files.• Most logging is optional; you use server

startup options to enable just the logs you need

• Logs can grow quite large, so it's important to make sure they don't fill up your filesystem.

• You can expire the logs periodically to keep the amount of space that they use within bounds.


Error log

• Contains a record of diagnostic information produced by the server when exceptional conditions occur.

• If the server fails to start up or exits unexpectedly, this log is useful because it will often contain the reason why.


General query log

• Provides general information about server operation: who is connecting from where and what statements they are issuing.


Binary log• Statements that modify database contents. • Also contains information such as timestamps

needed to keep slave servers synchronized when the server is a master server in a replication setup.

• The contents of the binary log are written in binary format as "events" that can be executed by providing them as input to the mysql client.

• The accompanying binary log index file lists which binary log files the server currently is maintaining.


Binary log

• Useful if you have a crash and must revert to backup files

• Because you can repeat the updates performed after the backup was made by feeding the log files to the server.

• This enables you to bring your databases up to the state they were in when the crash occurred.

• Used if you set up replication servers, because it serves as a record of the updates that must be transmitted from a master server to slave servers.


Binary log


• columns for date and time, • server thread ID (connection ID), • event category, • event-specific information.

Secure Log Files

• Make sure that your log files are secure and not readable by arbitrary users

• May contain the text of statements that include sensitive information such as passwords.

• For example, the following log entry displays the password for the root user


MySQL Administration The Mysql Data Directory

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