Hi!
>>>>> "MARK" == MARK CALLAGHAN <mdcallag@stripped> writes:
MARK> On Fri, Jan 29, 2010 at 11:29 AM, Michael Widenius <monty@stripped>
> wrote:
>>
>> Hi!
>>
>>>>>>> "Paul" == Paul McCullagh <paul.mccullagh@stripped>
> writes:
Paul> It would be easy to tell the start and end of statements if these
Paul> functions were only called ONCE for each statement.
>>
Paul> However, if multiple tables are involved in a statement (which is not
Paul> the case in the example above), then start_stmt() and reset() are
Paul> called multiple times for each statement.
>>
Paul> So how do I know where the actual boundaries of the statements are?
>>
>> Why not simply have a counter in your transaction object for how
>> start_stmt - reset(); When this is 0 then you know stmnt ended.
>>
>> In Maria we count number of calls to external_lock() and when the sum
>> goes to 0 we know the transaction has ended.
MARK> Why does the solution need to be so obscure?
Historic reasons.
MySQL never kept a count of which handlers are used by a transaction,
only which tables.
So the original logic was that external_lock(lock/unlock) is called
for each usage of the table, which is normally more than enough
information for a handler to know when a statement starts/ends.
The one case this didn't work was in the case someone does lock
tables as then external_lock is not called per statement.
It was to satisfy this case that we added a call to start_stmt() for
each table.
It's of course possible to change things so that start_stmt() /
end_stmt() would be called once per used handler, but this would be
yet another overhead for the upper level to do which the current
handlers that tracks call to external_lock() doesn't need.
Regards,
Monty
