> On Mar 8, 2017, at 7:17 AM, Aldo Caruso aldo.car...@argencasas.com > [firebird-support] <firebird-support@yahoogroups.com> wrote: > > > > Thanks for your answer. > > Regarding the "blob not found" error, there is a thread about this issue [1] > > Nevertheless, I believe that RO/RC transactions are assigned a unique ID, > because as I start them the next transaction ID keeps incrementing. >
Right. They're precommitted but do get unique ids. I'm getting old Cheers, Ann > [1] > https://groups.yahoo.com/neo/groups/firebird-support/conversations/topics/111668 > > Aldo Caruso > >> El 07/03/17 a las 15:52, Ann Harrison aharri...@ibphoenix.com >> [firebird-support] escribió: >> > On Mar 7, 2017, at 10:30 AM, Aldo Caruso >> > aldo.car...@argencasas.com wrote: >> >> > >> > Supposing a connection only needs to read from a database. Which are the >> > benefits of starting a read only transaction ? >> > >> I doubt that there is any difference in performance that you could measure. >> Almost all transactions change the database - cooperative garbage >> collection, incrementing the next transaction id on the header page, ending >> the transaction on the TIP. The security checks have to be made to insure >> read access - checking for higher levels is no more expensive. DEclaring a >> transaction to be read-only is a slight check on programmers - Firebird will >> detect and block writes that were added carelessly in a point version of an >> application. >> >> However, a read-only, read-committed transaction has merit if you don't need >> consistency. Firebird doesn't assign a unique transaction id to RO/RC >> transactions, so they don't change the next transaction id, they don't block >> garbage collection, and they don't change the state of a bit on a TIP. From >> time to time (IIRC) they'll return a "blob. not found" error if the record >> holding the blob is garbage collected between the time the RO/RC transaction >> reads the record and retrieves the blob. >> >> Basically, read-only was implemented decades ago to give InterBase a check >> mark on standard compliance and Firebird added a hack to provide low >> overhead, low consistency transactions. >> >> Good luck, >> >> Ann >> > > > >
