mysqlcheck: Check and Repair Tables & Databases

on Database Management Systems, MySQL • January 5th, 2022 • Write for Hevo

MySQL Check

mysqlcheck offers an efficient way to perform maintenance of tables and databases in MySQL. It can check tables, repair them if found corrupt, optimize them and perform combined operations of checking, repairing, and optimizing altogether. mysqlcheck command-line utility in MySQL is intended to be used when the mysqld server is running. It can execute CHECK TABLE, REPAIR TABLE, ANALYZE TABLE and OPTIMIZE TABLE statements in the most convenient way for the user.

In this blog, we explore the different ways of using mysqlcheck command line for checking, repairing, and optimizing tables and databases in MySQL. Start verifying and taking corrective actions for your tables and databases using this guide. 

Table of Contents

What is MySQL?

MySQL Logo: mysqlcheck
Image Source: Logo Wine

MySQL is the world’s most popular Open Source Relational Database Management System (RDBMS) used by all types of Small and Medium-Size Businesses (SMBs) and large enterprises. MySQL was initially developed, marketed, and supported by MySQL AB, a Swedish company but later got acquired by Sun Microsoft Systems (currently known as Oracle Corporation). Just like other typical databases, MySQL can store user/business/customer information in the form of rows and columns in a table. It provides referential integrity between rows and columns of various tables and processes user requests using SQL

MySQL holds a highly regarded name in businesses working with databases and Cloud-based Data Warehousing solutions. It’s scalable, reliable, and user-friendly. It also works cross-platform which means that users can run MySQL on Linux and Windows, and restore backups from the other platform. 

Business Benefits of Using MySQL

MySQL is popular all over the world and is used by leading tech giants owing to the following reasons:

Easy to Install and Deploy

Businesses can set up and run SQL queries on their data using MySQL in minutes. MySQL enables them to deliver new applications faster than proprietary databases.

High Speed

It’s a no-brainer that if you are working with large datasets, you wouldn’t want to spend an extensive amount of time working with datasets and tables. Unlike other databases, MySQL is comparatively faster and can query information from large datasets helping in business intelligence activities.

Read more on the top 10 MySQL ETL tools for your business here. 

Industry Standards

Whether you are a developer who is required for rapid development of software or a freelancer who seeks to work with databases, MySQL has been in use for over 20 years and you can be sure of using MySQL as a fully integrated transaction-safe, ACID-compliant database.

Reliability and High Availability

MySQL has a well-established reputation for reliability among its 5 million user base. In addition to reliability, MySQL Cluster gives 99.999 percent availability.

Multiple Platform Support

MySQL can be used on 20 platforms including Linux, Solaris, AIX, HP-UX, Windows, and Mac OS X. This provides organizations with complete flexibility in delivering a solution on the platform of their choice.

What is mysqlcheck Client?

mysqlcheck client: mysqlcheck
Image Source: Globo.Tech

mysqlcheck is a table maintenance program to check, repair, optimize, or analyze multiple tables from the command line. It works with InnoDB, MyISAM, and ARCHIVE tables and provides three levels of checking:

  • Table-specific
  • Database-specific
  • All databases

mysqlcheck table client for MySQL consists of four SQL statements to perform the table maintenance action:

  • CHECK TABLE, 
  • REPAIR TABLE, 
  • ANALYZE TABLE, and 
  • OPTIMIZE TABLE

While performing table repair or analysis, it is important to bear in mind that table maintenance operations like mysqlcheck can become time-consuming processes especially when you have a large number of entries in your tables. If you use the –databases or –all-databases option to process all tables in one or more databases, a mysqlcheck call might take you a long time to complete. 

Note: For performing mysqlcheck operation, you must run the mysqld server. This means that you do not have to stop the server to perform table maintenance. mysqlcheck is different from myisamchk and aria_chk utilities that don’t require the server to be running.

mysqlcheck Command

There are three ways to use mysqlcheck command-line tool:

./client/mysqlcheck [OPTIONS] database [tables]
./client/mysqlcheck [OPTIONS] --databases DB1 [DB2 DB3...]
./client/mysqlcheck [OPTIONS] --all-databases

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Using mysqlcheck for MySQL Database Tables

Important Note: Before we proceed with table check, repair, or analysis operations, it’s best advised to create a backup of your table(s), for some circumstances might lead to a potential data loss. 

As a result, we’ve split this tutorial into four sections for your convenience:

Part 1: Creating a MySQL Database Back-Up

To create a backup of all your existing MySQL databases, follow these steps:

Step 1: Log in to your MySQL server using Secure Shell (SSH).

Step 2: Stop MySQL server using the appropriate command based on your Linux distribution:

For CentOS and Fedora, type:

service mysqld stop

For Debian and Ubuntu, type:

service mysql stop

Step 3: Input the following command to copy all of your databases to a directory name based on the current time.

cp -rfv /var/lib/mysql /var/lib/mysql$(date +%s)

Step 4: Restart MySQL server with the command appropriate for your Linux distribution:

For CentOS and Fedora, type:

service mysqld start

For Debian and Ubuntu, type:

service mysql start

Part 2: Running mysqlcheck Command

To use the mysqlcheck table command and check tables, follow these steps:

Step 1: As an administrator, change your directory to MySQL Data Directory.

cd /var/lib/mysql

Step 2: Now type in the mysqlcheck command to check for an existing table in a database. In our example, we are checking for a table called “email” under the database “customers”.

$ mysqlcheck -c customers email
customers.email                         OK

Notice our result. If a table passes the check, mysqlcheck displays OK for the table.

Not only this, mysqlcheck command can be used to CHECK (-c, -m, -C), REPAIR (-r), ANALYZE (-a), or OPTIMIZE (-o) table within your databases. The -c, -r, -a, and -o options work exclusively.

Some of the options (like -e (–extended) or -q (–quick)) can also be used at the same time but not all options are supported by all storage engines.

Running mysqlcheck to Analyze a Table in MySQL Database

As an example, the following command analyzes the “email” table within our “customers” database:

$ mysqlcheck -a customers email
customers.email                         OK

Running mysqlcheck to Repair Tables in a MySQL Database

The following command repairs all tables in the “customers” and “leads” databases:

$ mysqlcheck -r --databases customers leads

Note: If you see a note stating: The storage engine for the table doesn’t support repair it means that you are doing REPAIR on an InnoDB.

Running mysqlcheck to Optimize Tables in a MySQL Database

The following mysqlcheck database command optimizes all tables in all your MySQL databases.

$ mysqlcheck -o --all-databases

For user reference, this is a table showcasing the most used options for the mysqlcheck database command.

Option Description
-c, –checkCheck the tables for errors
-a, –analyzeAnalyze the tables
-o, –optimizeOptimize the tables
-r, –repairPerform a repair that can fix almost anything except unique keys that are not unique
–auto-repairIf a checked table is corrupted, automatically fix it
-A, –all-databasesCheck all tables in all databases. This is the same as –databases with all databases selected
-B, –databasesProcess all tables in the named databases. With this option, all name arguments are regarded as database names, not as table names
–tablesOverrides the –databases or -B option such that all name arguments following the option are regarded as table names
-g, –check-upgradeCheck tables for version-dependent changes. It may be used with –auto-repair to correct tables requiring version-dependent updates
–compressCompress all information sent between client and server
–debug-infoPrint debugging information, memory, and CPU statistics when the program exits
-e, -–extendedCheck and repair tables
-q, –quickThe fastest method of checking
-?, –helpDisplay a help message and exit

A more extensive list of other mysqlcheck database command options can be found on this page.

Likewise, these mysqlcheck table/database options can be combined together to perform a joint operation. Have a look at how this can be performed in the following section.

Part 3: Using mysqlcheck in Compound Commands

The mysqlcheck command-line utility can be extended for giving compound commands. For instance, let’s assume a case where there is a need to repair and optimize the “email” table from our previously stated “customer” database. 

mysqlcheck table command options like  -c (check), -r (repair), -a (analyze), and -o (optimize) options work exclusively and can be used concurrently in the same mysqlcheck command.

Running mysqlcheck to Optimize and Repair Tables in a MySQL Database

The following mysqlcheck command checks, optimizes, and auto-repairs all corrupted tables in the “customer” database. The auto repair option automatically fixes a checked table if found corrupted.

$ mysqlcheck --auto-repair -o customers

And the following mysqlcheck command optimizes and auto-repairs all tables in all your MySQL databases.

$ mysqlcheck --auto-repair -o --all-databases

Part 4: mysqlcheck Command Modifications

The command mysqlcheck can be altered, changing its default behavior from checking tables (–check) to repairing or optimizing tables. This can be done by changing the binary “checkand replacing it with “repair”, or “analyze”, or “optimize”.

These are the commands you get after substitution:

CommandMeaning
mysqlrepairThe default option is –repair
mysqlanalyzeThe default option is –analyze
mysqloptimizeThe default option is –optimize

All these commands when invoked would perform the same operation as mysqlcheck -[option] when used. 

If you would like to learn about MySQL database export command-line utility, see our blog on MySQL Export Database Command Line: 3 Easy Methods. If you would like to know more about MySQL Analytics tools, visit our other informative blog here- MySQL Analytics Tools: A Quick Guide.

Conclusion

mysqlcheck table/database commands are ideal for automated optimizations of MySQL databases and tables. The more your database expands and the number of tables increases, the more likely it is that your tables/databases will encounter mistakes from time to time. In those circumstances, mysqlcheck can be a lifesaver.

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Share your most frequently used MySQL commands, as well as those for your tables and databases. Suggest to us any more MySQL topics you’d like us to cover in the comments below. We’d appreciate hearing from you.

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