Re: Long transaction & LOG_CHECKPOINT_INTERVAL

Richard Foote wrote:

> Hi
>
> I'm not sure I understand your understanding but I hope this helps.
>
> Providing log_checkpoint_interval is the most aggressive of the checkpoint
> targets, once exceeded, DBWRs are requested to write down those blocks that
> correspond to the oldest redo that exceeds the log_checkpoint_interval. Once
> complete, we now only have to recover the log_checkpoint_interval amount of
> redo during instance recovery.
>
> From this point on, subsequent writes to the redo log will again exceed this
> target and so DBWR is continually requested to write these offending blocks
> to disk (note if these blocks are still in memory).
>
> With your long transaction, once it has generated log_checkpoint_interval
> amount of redo, it's earlier changed blocks are being written down by DBWRs
> to ensure instance recovery requirements are met.

Thank you, Richard!
But I still can't understand this issue. Yes, I do believe the DBWRs would flush the dirty blocks which both the long tx and other transactions made when whatever conditions trigger log_checkpoint_interval. The problem is even so, the long transaction is still active, at this moment, if the instance crash, during the recovery, the long tx have to be rollback. it need to reapply those undo blocks (either they flush to disk during the checkpoint or not) to do the rollbak. How to gurantee those number of undo blocks must less than the log_checkpoint_interval number of redo blocks.

>
>
> Depending on the performance of DBWRs, it might not quite be able to keep up
> and in actuality more than log_checkpoint_interval of redo may need to be
> recovered but Oracle is actively trying to keep to this target and all
> things being equal should be there or thereabouts (see v$instance_recovery).
>
> Hope this helps
>
> Richard
>
> "Y" <y_at_y.y> wrote in message news:3CFC29FD.97A707EC_at_y.y...
> > Why we say LOG_CHECKPOINT_INTERVAL ensures that no more than
> > log_checkpoint_interval number of redo blocks are read during instance
> > recovery.
> >
> > Checkpoint only ensures those dirty pages in buffers will be written to
> > disk. If there is a long transaction which will span more than one log
> > file. During the instance recovery, there are maybe more than
> > log_checkpoint_interval will be need to be read.
> >
> > Would you tell me where my understanding is wrong?
> >
> > TIA
> >
Received on Mon Jun 10 2002 - 22:40:44 CDT