No -- Facebook's PHP code is translated to C++ by HipHop and compiled into a monolithic binary, and Cassandra has largely been deprecated in favor of HBase.
"Facebook uses hphpi (and now hhvm) for day-to-day software development, but uses the HipHop compiler (hphpc) to create optimized binaries that serve the Facebook website. hphpc is in essence a traditional static compiler that converts PHP→AST→C++→x64."
