Hi!
Any new PHP major release is about setting new directions. I, Andrey and
Johannes, the guys maintaining ext/*mysql* recommend going mysqlnd after
an "incubation" of some four years (5.3x series + dev time).
My concern was also that making mysqlnd the default would make libmysql support considered secondary and unimportant. As I was assured it is not the case and the differences between mysqlnd and libmysql flavors seem to be rectified or in the process of being rectified, and I heard no objections for this as a default, I'm OK with it now.
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Stanislav Malyshev, Software Architect
SugarCRM: http://www.sugarcrm.com/
(408)454-6900 ext. 227