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Re: Future development

From: Bart Samwel <bart(at)samwel(dot)tk>
To: Ludek Finstrle <luf(at)pzkagis(dot)cz>
Cc: pgsql-odbc(at)postgresql(dot)org
Subject: Re: Future development
Date: 2006-03-22 12:38:41
Message-ID: 44214551.5060202@samwel.tk (view raw or flat)
Thread:
Lists: pgsql-odbc
Ludek Finstrle wrote:
>> I for one can't live without the "Level of rollback on errors" feature 
>> of the 7.3 experimental branch. I don't care about which branch is used, 
>> as long as this feature is in there -- the 8.1 branch doesn't work for 
>> me at all. :-/
> 
> Could you explain me the "Level of rollback on errors"? I think that
> when programmer doesn't use autocommit mode he want react on errors
> himself.

Like I said in my other message, the 8.01 driver doesn't give me a 
choice in how to react on errors at all: it forces me to rollback the 
complete transaction. I want to have a choice in that. The 7.03 driver 
allows me to set the "Level of rollback on errors" to "Statement", which 
means that only the failed statement is rolled back, and *I* then have 
the choice of whether I want to rollback the remainder of the 
transaction as well, or that I want to continue / try something else.

Another example of a situation where the per-statement rollback on 
errors is wanted. Situation sketch: we have a client-side object model 
with a generic persistence layer that stores the objects in a SQL 
database. When we save changes, we try to store all of the objects 
WITHOUT deferring constraints, even though there may be circular 
references etcetera. The reason for not deferring constraints is that we 
want to be able to tell the user which objects are the cause of 
constraint violations, something which isn't possible when you simply 
get "constraint XXX violated" at commit time. So, what we do is, we try 
to store every object, skipping any that fail, then we try the failed 
ones again, as long as the set of objects gets smaller. Then only at the 
end do we try and defer constraints in order to store the last ones. But 
if we can't deliberately try statements, knowing that they might fail 
(atomically), this doesn't work. It works on all other databases that we 
support, it works on PostgreSQL with the 7.03 driver with "Level of 
rollback on errors" set to "Statement", it just doesn't work with the 
8.01 driver because it will force us to roll back the transaction.

Cheers,
Bart

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