content_image/742410.jpg
Empty set, 2 warnings (0.00 sec) 

To work around this, you can use a comparison based on the UTC value actually stored in the column, which has the leap second correction applied: 

## 5.1.16 Resource Groups 

mysql> -- selecting using UNIX_TIMESTAMP value return leap value mysql> SELECT * FROM t1 WHERE UNIX_TIMESTAMP(ts) = 1230768000; +------+---------------------+ | a | ts | +------+---------------------+ | 2 | 2008-12-31 23:59:59 | +------+---------------------+ 1 row in set (0.00 sec) 

MySQL supports creation and management of resource groups, and permits assigning threads running within the server to particular groups so that threads execute according to the resources available to the group. Group attributes enable control over its resources, to enable or restrict resource consumption by threads in the group. DBAs can modify these attributes as appropriate for different workloads. 

Currently, CPU time is a manageable resource, represented by the concept of “virtual CPU”  as a term that includes CPU cores, hyperthreads, hardware threads, and so forth. The server determines at startup how many virtual CPUs are available, and database administrators with appropriate privileges can associate these CPUs with resource groups and assign threads to groups. 

For example, to manage execution of batch jobs that need not execute with high priority, a DBA can create a Batch  resource group, and adjust its priority up or down depending on how busy the server is. (Perhaps batch jobs assigned to the group should run at lower priority during the day and at higher priority during the night.) The DBA can also adjust the set of CPUs available to the group. Groups can be enabled or disabled to control whether threads are assignable to them. 

## Resource Group Elements 

The following sections describe aspects of resource group use in MySQL: 

•Resource Group Elements 

•Resource Group Attributes 

•Resource Group Management 

•Resource Group Replication 

•Resource Group Restrictions 

<img src='content_image/742410.jpg'>

## Important 

On some platforms or MySQL server configurations, resource groups are unavailable or have limitations. In particular, Linux systems might require a manual step for some installation methods. For details, see Resource Group Restrictions. 

These capabilities provide the SQL interface for resource group management in MySQL: 

•SQL statements enable creating, altering, and dropping resource groups, and enable assigning threads to resource groups. An optimizer hint enables assigning individual statements to resource groups. 

•Resource group privileges provide control over which users can perform resource group operations. 

