Fix two problems:
- The value of mysqli_get_client_info() has been changed recently and did
not include "mysqlnd" anymore thus the test suite was thinking the build
is always libmysql. This did not kept the suite from running pconn tests
- Going back to the libc allocator because the memory arena could be on a
persistent connections. If the build is not debug there will be no error
but the memory will be freed and in the second use of this pconn freed
memory will be used - not good! For now the arena doesn't take an argument
whether it should allocate persistently or not, thus persistent is safe
for now.
Johannes gave his +1 to commit this.
Memory usage optimisation. mysqlnd is not libmysql. mysqlnd does use the
Zend allocator, which means that is easier to hit memory_limit if you
have big stored (buffered) result sets. Before with libmysql you won't
hit memory_limit because libmysql uses libc's allocator and nothing is
checked. Now, with mysqlnd the situation is stricter and it is easier to
hit memory_limit. We try to optimize for big result sets. If a result set
is larger than 10 rows we will start freeing some data to keep memory usage
after 10 rows constant. This will help in the cases where a buffered result
set is scrolled forward only and just only once, or mysqlnd will need to
decode data from the network buffers again - yes, it is a trade-off between
CPU time and memory size. The best for big result sets is of course using
unbuffered queries - for comparison : 3 Million rows with buffered take
at least 180MB, with buffered you will stay at 3MB, and unbuffered will be
just 7-8% slower.
Hardwire function call instead of using callbacks. We don't actually need
callbacks, it was done for making 2 functions static, not to pollute the
global functions space but that had its price of 8 bytes overheat per
allocation, which is just too much. Also making the app member 32b instead
of 64b, which should save additional 4 byte, to the total of 12 byte per
allocation of a row buffer.
