Do yourself a favour and use mysqlnd. mysqlnd has no isuses here.
If you insist on using the MySQL Client Library (libmysql) I strongly recommend to use mysqli_stmt_store_result() when fetching geometry data using prepared statements. When streaming data, which is the default for prepared statements, ext/mysqli will have to make a guess on the size of the result buffer it needs. The guess is based on a length reported by the MySQL CLient Library (libmysql). The MySQL Client Library reports 4GB (!) for a POINT - a conservative and safe guess. Consequently, ext/mysqli will try to allocate 4GB of RAM. The true (maximum) size of the column is not available before buffering the result on the client using mysqli_stmt_store_result(). If you call mysqli_stmt_store_result(), the result buffers will not get bigger than needed. However, store_result()/buffering is usually not what you want when you ask for prepared statements.
