In respect to the organization of modules, this really belongs in terminology_use_previous.h. More...

Classes
struct	compatible_name_t
	Encapsulates a <name, version> pair, holding an instrumentation name, and the version before which it was in use by the server. More...

Enumerations
enum	enum_compatibility_version { NONE , BEFORE_8_0_26 , BEFORE_8_2_0 }
	Enumeration holding the possible values for @terminology_use_previous. More...

Functions
compatible_name_t	lookup (PFS_class_type class_type, const std::string &str, bool use_prefix=true)
	For a given PFS_class_type, and a name within that class, return the version-dependent alias for that name. More...

bool	is_older_required (enum_compatibility_version version)
	Checks the session variable @session.terminology_use_previous, to determine whether an instrumented object that was renamed in the given version should use the old name. More...

Detailed Description

In respect to the organization of modules, this really belongs in terminology_use_previous.h.

However, that would create a cyclic dependency between header files:

enum_compatibility_version is needed in pfs_instr_class.h
PFS_class_type is defined in pfs_instr_class.h and needed in instrumentation_class_compatibility.h

So we keep enum_compatibility_version in its own header, included from both the other headers, to avoid the cyclicity.

Enumeration Type Documentation

◆ enum_compatibility_version

enum terminology_use_previous::enum_compatibility_version

Enumeration holding the possible values for @terminology_use_previous.

Each element corresponds to a server release where some instrumentation name was changed.

Enumerator
NONE	Use new names; do not provide backward compatibility.
BEFORE_8_0_26	Use names that were in use up to 8.0.25, inclusive.
BEFORE_8_2_0	Use names that were in use before 8.2.0.

Function Documentation

◆ is_older_required()

bool terminology_use_previous::is_older_required ( enum_compatibility_version version )

Checks the session variable @session.terminology_use_previous, to determine whether an instrumented object that was renamed in the given version should use the old name.

Parameters

version The version where the instrumentation name was renamed.

Return values

true	The old instrumentation name should be used.
false	The new instrumentation name should be used.

◆ lookup()

compatible_name_t terminology_use_previous::lookup	(	PFS_class_type	class_type,
		const std::string &	str,
		bool	use_prefix = `true`
	)

For a given PFS_class_type, and a name within that class, return the version-dependent alias for that name.

This is used when registering performance_schema names, to check if there are any alternative names. If there are, those are stored in the PFS_instr_class object. Later, when the name is required (e.g. during the execution of SELECT * FROM performance_schema.threads statement), it decides which name to use based on the value of @session.terminology_use_previous and the fields that were stored in PFS_instr_class.

This framework is extensible, so in future versions we can rename more names, and user will be able to choose exactly which version's names will be used. However, note that the framework currently does not support successive changes of the same identifier. This limitation allows us to return just a singleton compatible_name_t from this function. If, in the future, we need to make successive changes to the same identifier, this function needs to be changed so that it returns something like a std::map<ulong, char*>, for a given instrumented object mapping versions to alternative names.