The original motivation for this commit was that shared_ptr_helper used
std::shared_ptr<>() which does two heap allocations instead of
make_shared<>() which does a single allocation. Turned out that
1. the affected code (--> Storages/) is not on a hot path (rendering the
performance argument moot ...)
2. yet copying Storage objects is potentially dangerous and was
previously allowed.
Hence, this change
- removes shared_ptr_helper and as a result all inherited create() methods,
- instead, Storage objects are now created using make_shared<>() by the
caller (for that to work, many constructors had to be made public), and
- all Storage classes were marked as noncopyable using boost::noncopyable.
In sum, we are (likely) not making things faster but the code becomes
cleaner and harder to misuse.
Default settings are not very efficient, since they do not even reuse
connections.
And when each query requires connection you can have only ~80 QPS, while
by simply enabling connection reuse (connection_auto_close=false) you
can have ~500 QPS (and by increasing connection_pool_size you can have
better QPS throughput).
So this patch allows to pass through some connection related settings
for the StorageMySQL engine, like:
- connection_pool_size=16
- connection_max_tries=3
- connection_auto_close=true
v2: remove connection_pool_default_size
v3: remove num_tries_on_connection_loss
