Re: why is imp_xxh stored in an SV?

> Note that this and the just-submitted DBIS patch represent the end of
> my work on improving performance on DBI, (not counting any remedial work
> that may be required).

PS - here are some final timings, comparing my
    'while ($sth->fetch()) {$c++}'
test loop (with unchanged DBD-mysql-4.020), against
(a) DBI r15098, just before the start of my changes;
(b) DBI r15266 plus my recent DBIS and mg_ptr tweaks:

Times are in CPU seconds, lower is better:

	         unthreaded        |      threaded 
            5.8.1   5.8.9  5.15.6  |  5.8.1   5.8.9  5.15.7
	    -----   -----  ------ -+  -----   -----  ------
(a)         15.28   14.84   15.11  |  42.86   48.92   47.72
(b)         13.01   12.44   12.68  |  27.81   30.19   17.67


Note especially how on modern threaded perls (i.e. >= 5.10), the timing
is approaching that of unthreaded. (I have a separate patch pending
against DBD-mysql which brings that 17.67 down by another 2.5 seconds)

All very satisfying :-)


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