To build custom listeners that work with the MySQL Connector/NET Trace Source, it is necessary to understand the key methods used, and the event data formats used.
The main method involved in passing trace messages is the
TraceSource.TraceEvent
method. This has the
prototype:
public void TraceEvent(
TraceEventType eventType,
int id,
string format,
params Object[] args
)
This trace source method will process the list of attached
listeners and call the listener's
TraceListener.TraceEvent
method. The
prototype for the TraceListener.TraceEvent
method is as follows:
public virtual void TraceEvent(
TraceEventCache eventCache,
string source,
TraceEventType eventType,
int id,
string format,
params Object[] args
)
The first three parameters are used in the standard as defined by Microsoft. The last three parameters contain MySQL-specific trace information. Each of these parameters is now discussed in more detail.
int id
This is a MySQL-specific identifier. It identifies the MySQL
event type that has occurred, resulting in a trace message being
generated. This value is defined by the
MySqlTraceEventType
public enum contained in
the Connector/NET code:
public enum MySqlTraceEventType : int
{
ConnectionOpened = 1,
ConnectionClosed,
QueryOpened,
ResultOpened,
ResultClosed,
QueryClosed,
StatementPrepared,
StatementExecuted,
StatementClosed,
NonQuery,
UsageAdvisorWarning,
Warning,
Error
}
The MySQL event type also determines the contents passed using
the parameter params Object[] args
. The
nature of the args
parameters are described
in further detail in the following material.
string
format
This is the format string that contains zero or more format
items, which correspond to objects in the args array. This would
be used by a listener such as
ConsoleTraceListener
to write a message to
the output device.
params Object[]
args
This is a list of objects that depends on the MySQL event type,
id
. However, the first parameter passed using
this list is always the driver id. The driver id is a unique
number that is incremented each time the connector is opened.
This enables groups of queries on the same connection to be
identified. The parameters that follow driver id depend on the
MySQL event id, and are as follows:
MySQL-specific event type | Arguments (params Object[] args) |
---|---|
ConnectionOpened | Connection string |
ConnectionClosed | No additional parameters |
QueryOpened | mysql server thread id, query text |
ResultOpened | field count, affected rows (-1 if select), inserted id (-1 if select) |
ResultClosed | total rows read, rows skipped, size of result set in bytes |
QueryClosed | No additional parameters |
StatementPrepared | prepared sql, statement id |
StatementExecuted | statement id, mysql server thread id |
StatementClosed | statement id |
NonQuery | Varies |
UsageAdvisorWarning | usage advisor flag. NoIndex = 1, BadIndex = 2, SkippedRows = 3, SkippedColumns = 4, FieldConversion = 5. |
Warning | level, code, message |
Error | error number, error message |
This information will allow you to create custom trace listeners that can actively monitor the MySQL-specific events.