Hi Aleksey,

I think that we should remove trx_t::start_time, and always use trx_t::start_time_micro.

I shortly discussed this with Vladislav Vaintroub, and he mentioned that the microsecond timestamp in THD::start_utime is updated at the start of each statement.

I also looked at his MDEV-12345 performance fix. It looks like trx_start_low() is already doing the right thing, except that the trx_t::start_time should be removed.

I'd welcome a contributed patch that removes trx_t:.start_time. Or if that really is too tricky, convert start_time_micro to start_time.

Marko

On Thu, Nov 16, 2017 at 11:29 AM, Aleksey Midenkov <midenok@gmail.com> wrote:

Hello!

Different semantics of these 2 members doesn't look good:

time_t start_time; /*!< time the state last time became
TRX_STATE_ACTIVE */
ib_uint64_t start_time_micro; /*!< start time of transaction in
microseconds */

Either `start_time_micro` should be drawn to the base of `start_time`
or it should be explicitly commented that it has nothing to do with
`start_time`. I.e. there is nothing wrong on algorithmic level, but
such data members may (and certainly would) lead developers to misuse
of `start_time_micro`.

--
All the best,

Aleksey Midenkov
@midenok

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