Re: Changing isolation level?

While stranded on information super highway ctcgag_at_hotmail.com wrote:
:)NoJunkMailshah_at_xnet.com wrote:
:)>
:)> First transaction reads a row and deletes it, the changes has not yet
:)> been commited.
:)
:)This sounds like something Advanced Queuing may be suited for.
:)
:)> Meanwhile the second transaction tries to read a row and get same row
:)> again, it has not yet deleted the row.
:)>
:)> First transaction commits the changes.
:)>
:)> When second transaction tries to delete the row it gets error.
:)
:)Fine. It gets an error: it's not like your server catches on fire. Catch
:)the exception and deal with it.

 It is not that simple. I was trying to give simple example, these  transactions deal with insurance policies, and when 2 of them are working on  same policy and run into problems applying premiums. I am not the application  programmer so I do not understand details of the process.

:)
:)>
:)> This is a part of big application and has worked with VSAM and DB2 where
:)> they lock the rows once someone updates or deletes it but has not yet
:)> commited.
:)
:)Do VSAM and DB2 block when they get to the locked row, or do they just
:)skip it?

 They skip over it unless I specifically ask for that row.

:)
:)>
:)> I may be wrong here, but if the row has been (marked for) updated or
:)> deleted and another transaction get old value then I consider it a dirty
:)> read.
:)
:)I dirty read is reading uncommitted data. It aint' doing that.
:)
:)> This may be O.K. in data warehouse but is not acceptable in online
:)> transaction.
:)
:)
:)> Imagine in a banking environment, you are withdrawing money from an
:)> account at the same time your spouse at another ATM is also trying to
:)> withdraw the money and he/she gets wrong balance.
:)
:)OK, I'm imagining. And in fact, I'm pretty sure that banks don't
:)guarantee that the balance given reflects even all recent transactions,
:)much less all uncompleted transactions, so I'm betting banks use an
:)Oracle-like model.
:)
:)Xho
:)
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