Using Persistent Connections
If mysqli is used with mysqlnd, when a persistent connection is created it generates a COM_CHANGE_USER (mysql_change_user()) call on the server. This ensures that re-authentication of the connection takes place.
As there is some overhead associated with the COM_CHANGE_USER call, it is possible to switch this off at compile time. Reusing a persistent connection will then generate a COM_PING (mysql_ping) call to simply test the connection is reusable.
Generation of COM_CHANGE_USER can be switched off with the compile flag MYSQLI_NO_CHANGE_USER_ON_PCONNECT. For example:
shell# CFLAGS="-DMYSQLI_NO_CHANGE_USER_ON_PCONNECT" ./configure --with-mysql=/usr/local/mysql/ --with-mysqli=/usr/local/mysql/bin/mysql_config --with-pdo-mysql=/usr/local/mysql/bin/mysql_config --enable-debug && make clean && make -j6
shell# export CFLAGS="-DMYSQLI_NO_CHANGE_USER_ON_PCONNECT" shell# configure --whatever-option shell# make clean shell# make
Note that only mysqli on mysqlnd uses COM_CHANGE_USER. Other extension-driver combinations use COM_PING on initial use of a persistent connection.