[Gnumed-devel] Re: [NOVICE] idiom for interactive client applications.

[Syan Tan]

And close the previous transaction when a suitable granularity of focus changes,
eg before  a editable table gains input focus,  a tab change , or another node 
of
the tree is selected.

On Sat Oct 13  4:28 , Syan Tan  sent:

>
>select for update just protects from having the transaction being aborted later
>on, otherwise
>it will block if someone else is updating. it doesn't address the issue of 
>having
>client cached 
>values being changed outside of a transaction. holding one transaction only to
>interactively update a complex object would be more headache due to cascading
>abort, then just issuing an exclusive lock on all items related to the object (
>e.g by writing a lock into a lookup table against the object's id), which isnt
>what's wanted. opening the transaction just before an update means each write
>needs to be checked manually for a conflict, because the user only sees a 
>cached
>old value, which might have changed because no transaction was open whilst the
>user was  browsing of the object.
>It's probably to do with the complexity of the user interface structure; some
>user interfaces only display one page of  one view at the most , so that at 
>most
>opening a transaction with each user page involves locking only a few rows of 
>one
>or two tables, so it would make sense to do as below, but for an application 
>that
>edits data for a complex obect composed of 10 or more tables,
>it might not be sensible.
>I suppose there's the answer then, open up a transaction every time the tab 
>page
>is changed
>or a tree node is selected, and select for update everything that is being
>displayed and editable.
>
>
>
>On Fri Oct 12 20:49 , Richard Broersma Jr  sent:
>
>>--- syan tan wrote:
>>> What other ways are there of doing such an app?
>>
>>The two ways that I know of are:
>>
>>BEGIN TRANSACTION ISOLATION LEVEL SERIALIZABLE;
>>
>>--if the tuple was modified by another transaction, this transaction will fail
>on commit.
>>
>>SELECT FOR UPDATE... -- pre-lock the tuple of interest from other commits.
>>
>>Regards,
>>Richard Broersma Jr.
>>
>>---------------------------(end of broadcast)---------------------------
>>TIP 7: You can help support the PostgreSQL project by donating at
>>
>>                http://www.postgresql.org/about/donate
>
>
>
>---------------------------(end of broadcast)---------------------------
>TIP 7: You can help support the PostgreSQL project by donating at
>
>                http://www.postgresql.org/about/donate