Re: log_checkpoint_timeout : what is exactly the meaning ?

"Jonathan Lewis" <jonathan_at_jlcomp.demon.co.uk> a écrit dans le message news: 1022835785.7919.0.nnrp-10.9e984b29_at_news.demon.co.uk...
>
> Richard,
> Thanks for the correction. I think in future I'll avoid making
> any comments about Oracle behaviour when I've just
> spent 22 hours on a plane.
>
> Vigi98,
> The choice of FIRST is deliberate and correct. Looking
> at it another way around - when you first change a data
> block it goes onto a 'checkpoint queue' waiting to be
> written to disc. This queue is a linked list of buffer headers,
> protected by a latch. Once a buffer header is in the
> list, its position is not changed regardless of how many
> times the content of the block change. Setting the
> checkpoint timeout to 900 seconds ensures that the
> length of the queue is never allowed to get too long -
> any block that joined the queue more than 900 seconds
> ago will have been written back to disc.
>
> Alternatively - if I look for a piece of the redo log that I
> generated over 900 seconds ago, then the block that I
> applied it to has definitely been written to disc at some
> time in the interim.
>

Sorry for my insistance, but it's still not clear to me. Does what you say mean that checkpoints are always completed in exactly 15 minutes (in case there is a low traffic, so that redo log switch occur in more than 15') ?

> --
> Jonathan Lewis
> http://www.jlcomp.demon.co.uk
>
> Author of:
> Practical Oracle 8i: Building Efficient Databases
>
> Next Seminar - Australia - July/August
> http://www.jlcomp.demon.co.uk/seminar.html
>
> Host to The Co-Operative Oracle Users' FAQ
> http://www.jlcomp.demon.co.uk/faq/ind_faq.html
>
>
>
> Vigi98 wrote in message <3cf73625$0$247$626a54ce_at_news.free.fr>...
> >
> >"Richard Foote" <richard.foote_at_bigpond.com> wrote in message
> >news:%6EJ8.1685$Hj3.5395_at_newsfeeds.bigpond.com...
> >> Just a slight clarification to Jonathan's post.
> >>
> >> "... you are telling Oracle (not) to ensure that no block may remain
> >> unwritten if its first change occurred more than 900 seconds ago" (Note
> >the
> >> elimination of the "(not)" after Oracle correctly changes the meaning
of
> >the
> >> sentence)
> >>
> >> Cheers
> >>
> >> Richard
> >
> >Thanks for that precision, but the sentence remains unclear for me. Isn't
> it
> >"you are telling Oracle to ensure that no block may remain unwritten if
its
> >LAST change occurred more than 900 seconds ago" ?
> >
> >
> >>
> >> "Jonathan Lewis" <jonathan_at_jlcomp.demon.co.uk> wrote in message
> >> news:1022789937.15172.0.nnrp-12.9e984b29_at_news.demon.co.uk...
> >> >
> >> > The answer depends on your version of Oracle.
> >> > Recently the meaning has changed - Oracle uses
> >> > an incremental checkpoint strategy to ensure that
> >> > the I/O subsystem is not flooded so ferociously at
> >> > end of log file. The log_checkpoint_interval and
> >> > log_checkpoint_timeout had their implementation
> >> > changed so that they act as lag events, rather
> >> > than triggering a checkpoint.
> >> >
> >> > For log_checkpoint_timeout=900, you are telling
> >> > Oracle not to ensure that no block may remain
> >> > unwritten if its first change occurred more than
> >> > 900 seconds ago.
> >> >
> >> >
> >> > --
> >> > Jonathan Lewis
> >> > http://www.jlcomp.demon.co.uk
> >> >
> >> > Author of:
> >> > Practical Oracle 8i: Building Efficient Databases
> >> >
> >> > Next Seminar - Australia - July/August
> >> > http://www.jlcomp.demon.co.uk/seminar.html
> >> >
> >> > Host to The Co-Operative Oracle Users' FAQ
> >> > http://www.jlcomp.demon.co.uk/faq/ind_faq.html
> >> >
> >> >
> >> >
> >> > vigi98 wrote in message ...
> >> > >Hi all,
> >> > >
> >> > >In my init.ora, the only two parameters about checkpoints are the
> >> > >following :
> >> > >
> >> > >log_checkpoint_timeout = 900
> >> > >log_checkpoints_to_alert=true
> >> > >
> >> > >Shouldn't I observe in the alert file the beginning of a new
> >> > >checkpoint every 15 minutes ? Apparently checkpoints behave as if I
> >> > >had not set the log_checkpoint_timeout, i.e. checkpoints are
launched
> >> > >only when a redo log switch occurs. As my redo logs are 200Mb wide,
> >> > >there can be a very long time before a redo log switch occurs, in
case
> >> > >of low traffic on the database.
> >> > >
> >> > >Have I misunderstood the signification of this parameter (I mean
> >> > >log_checkpoint_timeout ) ?
> >> > >
> >> > >Thanks in advance.
> >> >
> >> >
> >>
> >>
> >
> >
>
>
Received on Fri May 31 2002 - 09:15:10 CDT