Performance schema likely/unlikely assume that performance schema
is enabled by default, which causes a performance degradation for
default installations that doesn't have performance schema enabled.
Fixed by changing the likely/unlikely in PS to assume it's
not enabled. This can be changed by compiling with
-DPSI_ON_BY_DEFAULT
Other changes:
- Added psi_likely/psi_unlikely that is depending on
PSI_ON_BY_DEFAULT. psi_likely() is assumed to be true
if PS is enabled.
- Added likely/unlikely to some PS interface code.
- Moved pfs_enabled to mysys (was initialized but not used before)
- Added "if (pfs_likely(pfs_enabled))" around calls to PS to avoid
an extra call if PS is not enabled.
- Moved checking flag_global_instrumention before other flags
to speed up the case when PS is not enabled.
This change is for performance optimization.
Fixed the performance schema instrumentation interface as follows:
- simplified mysql_unlock_mutex()
- simplified mysql_unlock_rwlock()
- simplified mysql_cond_signal()
- simplified mysql_cond_broadcast()
Changed the get_thread_XXX_locker apis to have one extra parameter,
to provide memory to the instrumentation implementation.
This API change allows to use memory provided by the caller,
to avoid having to use thread local storage.
Using this extra parameter will be done in a separate fix,
this change is for the interface only.
Adjusted all the code and unit tests accordingly.
