Tom Lane-2 wrote:
>
> It's not defined by the SQL standard, nor any other standard that I know
> of. So yes, different implementations might mean subtly different
> things by it.
>
OK, I see. Where can I find out the precise meaning of MVCC as in
PostgreSQL. I've read
http://www.postgresql.o
Kent Tong <[EMAIL PROTECTED]> writes:
> Is MVCC not well defined?
It's not defined by the SQL standard, nor any other standard that I know
of. So yes, different implementations might mean subtly different
things by it.
regards, tom lane
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Tom Lane-2 wrote:
>
> If you want that to fail, use a SELECT FOR UPDATE at steps 3/4.
>
> My interpretation of MVCC is that the above example isn't even
> meaningful, because it assumes that "writing into Y" is an overwrite,
> which it is not in Postgres --- that is, if T2 reads Y again, it'll
Kent Tong <[EMAIL PROTECTED]> writes:
> 1: T1 sets isolation to serializable & begins a transaction
> 2: T2 sets isolation to serializable & begins a transaction
> 3: T1 reads X into v1
> 4: T2 reads Y into v2
> 5: T1 writes v1 into Y
> 6: T2 writes v2 into X
> 7: T1 commits
> 8: T2 commits
> Obvi
Hi,
I read a description of MVCC in http://www.cs.ust.hk/~dimitris/CS530/L24.ppt
and
found that this isn't exactly what is implemented in PostgreSQL. For
example,
for a sequence of operations like:
1: T1 sets isolation to serializable & begins a transaction
2: T2 sets isolation to serializable &
