ADDM and Database Time

Database time is defined as the sum of the time spent inside the database processing user requests. 

The user’s response time is the time interval between the instant the request is sent and the instant the response is received. The database time involved in that user request is only a portion of that user’s response time that is spent inside the database.

The upper graphic in the slide above illustrates a simple scenario of a single user submitting a request. The user’s response time is the time interval between the instant the request is sent and the instant the response is received. The database time involved in that user request is only a portion of that user’s response time that is spent inside the database. 

 

The lower graphic in the slide illustrates database time as it is summed over multiple users, and each user is performing a series of operations resulting in a series of requests to the database. You can see that the database time is directly proportional to the number and duration of user requests, and can be higher or lower than the corresponding wall-clock time (elapsed time).

Using the database time as a measure, you can gauge the performance impact of any entity of the database. 

For example, the performance impact of an undersized buffer cache would be measured as the total database time spent in performing additional I/O requests that could have been avoided if the buffer cache were larger.

Database time is simply a measurement of the total amount of work done by the database server. The rate at which the database time is consumed is the database load average, measured as database time per second. 

The objective of ADDM is to reduce the amount of database time spent on a given workload, which is analogous to consuming less energy to perform the same task.