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Database Performance Troubleshooting - 9:48

Direct Link: https://vimeo.com/109263532

The following are sample screenshots from an AppDynamics for Databases MySQL collector. They illustrate the type of information collected for this database platform.

MySQL Current Window

The MySQL % CPU statistics are available on the Current window include the SL

The MySQL explain plan shows how the MySQL optimizer has decided to run a SELECT statement and access the data. MySQL can only explain SELECT statements.

The command syntax for viewing the EXPLAIN output is:

Code Block
explain [select statement]

For example:

Code Block
explain select count(*) from statistics where id = 5

The AppDynamics for Databases window displays the explain output for this command:

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The columns in the Explain plan table are:

id: The SELECT identifier. This is the sequential number of the SELECT within the query.

select_type: The type of SELECT, which can be any of those shown in the following table:

SIMPLE	Simple SELECT (not using UNION or subqueries)
PRIMARY	Outermost SELECT
UNION	Second or later SELECT statement in a UNION
DEPENDENT UNION	Second or later SELECT statement in a UNION, dependent on outer query
UNION RESULT	Result of a UNION.
SUBQUERY	First SELECT in subquery
DEPENDENT SUBQUERY	First SELECT in subquery, dependent on outer query
DERIVED	Derived table SELECT (subquery in FROM clause)

table: The table to which the row of output refers.

type: The join type.

possible_keys: The possible_keys column indicates which indexes MySQL can choose from use to find the rows in this table.

Key: The key column indicates the key (index) that MySQL actually decided to use. The key is NULL if no index was chosen. To force MySQL to use or ignore an index listed in the possible_keys column, use FORCE INDEX, USE INDEX, or IGNORE INDEX in your query.