histograms::Background_error_handler Class Reference

Custom error handling for histogram updates from the background thread. More...

Inheritance diagram for histograms::Background_error_handler:

Public Member Functions
bool	handle_condition (THD *, uint, const char *, Sql_condition::enum_severity_level *level, const char *) override
	Handle a sql condition. More...

Additional Inherited Members
Protected Member Functions inherited from Internal_error_handler
	Internal_error_handler ()
Internal_error_handler *	prev_internal_handler () const
virtual	~Internal_error_handler ()=default

Detailed Description

Custom error handling for histogram updates from the background thread.

Downgrades all errors to warnings. This is done for two reasons:

1) Because errors during background histogram updates are mostly ignorable, i.e., it is not critical that the user does something if histogram statistics fail to be updated.

2) We wish to throttle error log entries from background histogram updates, and this is currently only supported for a priority level of warnings.

Member Function Documentation

handle_condition()

bool histograms::Background_error_handler::handle_condition ( THD *  thd, uint  sql_errno, const char *  sqlstate, Sql_condition::enum_severity_level *  level, const char *  msg  )

inlineoverridevirtual

Handle a sql condition.

This method can be implemented by a subclass to achieve any of the following:

• mask a warning/error internally, prevent exposing it to the user,
• mask a warning/error and throw another one instead. When this method returns true, the sql condition is considered 'handled', and will not be propagated to upper layers. It is the responsibility of the code installing an internal handler to then check for trapped conditions, and implement logic to recover from the anticipated conditions trapped during runtime.

This mechanism is similar to C++ try/throw/catch:

• 'try' correspond to THD::push_internal_handler(),
• 'throw' correspond to my_error(), which invokes my_message_sql(),
• 'catch' correspond to checking how/if an internal handler was invoked, before removing it from the exception stack with THD::pop_internal_handler().

Parameters

thd	the calling thread
sql_errno	the error number for the condition raised.
sqlstate	the SQLSTATE for the condition raised.
level	the severity level for the condition raised.
msg	the error message for the condition raised.

Returns

true if the condition is handled

Implements Internal_error_handler.

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The documentation for this class was generated from the following file:

• sql/histograms/histogram.cc