maria-developers team mailing list archive

[Jan Lindström <jplindst@xxxxxxxxxxx>]

Hi,

I really do not see why you would want to define both algorithm and lock 
mode. In my transactional view
ALGORITHM=COPY would mean EXCLUSIVE lock and INPLACE would mean SHARED 
lock. Is there some
other lock that protects from concurrent online alter tables ? Lock NONE 
would mean I do not care what
happens.

R: Jan

> Hi,
>
> You've added this ALTER ONLINE TABLE syntax, where ONLINE de facto means
> "without copying the data".
>
> Now, after 5.6 merge we also have ALGORITHM=COPY|INPLACE and
> LOCK=NONE|SHARED|EXCLUSIVE.
>
> I've mapped ONLINE to ALGORITHM=INPLACE, because that's what it means.
>
> But it's confusing, one can have an "inplace" operation under an
> exclusive lock, if the engine wants it that way. And it won't be
> "online" by any stretch of imagination. One can also technically have a
> "copy" operation with a very permissive write-allow-write lock, and
> it'll be as online as one can get it.
>
> I mean, logically ONLINE should mean LOCK=NONE, not ALGORITHM=INPLACE.
> But that would change the existing behavior and the test results too.
> For example, *any* ALTER on the temporary table would always be
> "online", because, well, it wouldn't take any lock on that table.
> Alternatively, we can keep ONLINE as ALGORITHM=INPLACE, and deprecate
> it, issue a warning, suggesting to use the new 5.6 syntax.