i reread your emails, are you thinking something like this:
1)select * from table .... (very big)
2)update table (lock reads, very time consuming)
3)select * from table2 .... (very small, but i/o is very high and it will be very time consuming)
questions:
1)you want to pause 1 or 2 or 3?
2)maybe you want to pause 1 and 2, to make 3 faster since i/o?
3)after pausing a select, we can't execute update since select lock for read, and update for write, (maybe a row level lock allow it, but i think sometimes it can't do and update (2) will wait (1) end to start it job)
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there's some MDEV maybe it's what you need?
MDEV-4623 - lock/unlock connection (maybe this one)