Subject Re: [firebird-support] read only select statements and isolation
Author Mark Rotteveel
On 14-9-2015 09:45, Mark Rotteveel mark@...
[firebird-support] wrote:
> On 13-9-2015 04:33, thirdshiftcoder@... [firebird-support] wrote:
>> I read through and practiced with all types of read committed
>> transactions with and without wait. I understand those scenarios as they
>> apply to read write with, for i.e., update statements.
>> I am trying to figure out besides snapshot, which is the default
>> isolation in isql, how a select query would be useful when used in
>> another isolation level.
>> thanks for any examples.
> Depending on the isolation level, you will only see changes committed
> before your transaction started (eg snapshot), or any changes committed
> at the time they are read (read committed).
> This last feature might be useful if you are interested in timely
> information, not necessarily fully consistent data. Eg for something
> like a dashboard, having the latest information available can be more
> important.
> Also note that on other database systems, the transaction guarantees of
> something like snapshot can be more expensive, so read committed is
> usually "good enough" and people are more familiar with its behavior
> (usually implicitly); having an equivalent in Firebird makes it easier.

You might also want to read the chapter Working with Transactions in the
Interbase 6.0 Embedded SQL Guide. Specifically page 65 and on addresses
your question.

Mark Rotteveel