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Re: need help from the list admin




----- Am 1. Apr 2016 um 21:56 schrieb shawn l.green shawn.l.green@xxxxxxxxxx:

> Correct. MyISAM is not a transactional storage engine. It has no concept
> of COMMIT or ROLLBACK. Changes to it are controlled by a full table lock
> and as soon as the change is complete, the table is unlocked and is
> immediately visible to every other session.
> 
> What the replication system has done is to extend the length of that
> lock until the transaction completes to avoid situations where changes
> appear "out of sequence" to what is recorded in the Binary Log.

>> So when transaction is rollbacked, the inserted data in the MyISAM table remains
>> ?
> 
> Correct. All of the changes that could be undone were undone. MyISAM
> changes can't be undone so they stayed in place.
> 

Aah. OK.

> Try this as an analogy.
> 
> MyISAM tables are like writing directly with ink on paper. If you can
> complete the write, you have changed the row.
> 
> InnoDB tables are like whiteboards. You can undo your pending changes
> before someone else (one of the background threads of the InnoDB engine)
> makes the changes permanent.
> 
> The Binary Log is like a recipe used to rebuild your data in case it
> goes boom. If you start from a backup then repeat the sequence of
> actions as they were recorded in the Binary Log since that backup was
> created, you should wind up with exactly the same data you had before
> the problem.  If there is a problem with that sequence (actions are out
> of order) then rebuilding that data could be a problem.
> 
> Sequence makes a big difference even in less esoteric settings. Try this...
> 
> Start with your phone lying flat on your desk (screen up) pointing
> directly away from you. Roll it 45 degrees to the right. Now lift it
> vertically towards you 90 degrees (maintain the roll).  The phone is now
> pointing straight up but the screen is turned away from you.
> 
> Then try those same actions in reverse order. lift first, then roll it
> to the right. In this case the screen is pointing in your general
> direction but the whole thing is leaning off to one side.

I don't understand the example completely, but i understand
what you want to say: Changing the order of statements
may lead to a different result.

Bernd
 

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