Re: Checkpoints extreeeemely slow?

   I think he can still use 200Mb redo logs if he sets the log_checkopint_interval to a number os OS blocks equal to 20-25Mb.

   Best regards
   Luis Santos

On Thu, 6 Apr 2000 06:24:49 +0200, "Sybrand Bakker" <postbus_at_sybrandb.demon.nl> wrote:

>A redo log of 200M is ridiculous. 20-25M should be sufficient.
>And the disk array: let me guess, RAID-5?
>Means a performance penalty for any write activity, let alone sequential
>writes, as RAID-5 has parity checks.
>
>Hth,
>
>Sybrand Bakker, Oracle DBA
>
>Greg Stark <greg-spare-1_at_mit.edu> wrote in message
>news:874s9guq3f.fsf_at_HSE-Montreal-ppp33181.qc.sympatico.ca...
>>
>> I'm not sure I'm interpreting these numbers correctly, but they seem to be
>> implying that the cause of our performance problems is checkpoints that
 are
>> taking upwards of 15 minutes. Is that even possible? One question I have
 is if
>> 8.1.6 has a CKPT process running does that necessarily mean it's using it?
 The
>> CHECKPOINT_PROCSES parameter seems to be gone in 8i.
>>
>> I've been experimenting with the redo logs, at this point i have the least
>> variables I can expect to have: two redo logs on two different disks. Each
 is
>> 200Mb, it takes about 20m to switch. The log_checkpoint_timeout is 0 and
>> log_checkpoint_interval is 999999999.
>>
>> The intent is that checkpoints occur only on log file switches and always
 read
>> from the _other_ disk from the current active redo log.
>>
>> What's actually happening is that the checkpoint seems to go on and on for
>> about 15 minutes, nearly long enough to bring everything crashing to a
 halt as
>> it wraps around and runs into the active redo log. I believe the
 checkpoint is
>> happening because the following query continues to show two values with a
>> difference of one for this duration and because when I was dropping and
 adding
>> log files I received a 01624 on the not current log file.
>>
>> SQL> select * from v$sysstat where name like 'background checkpoints%';
>>
>> STATISTIC# NAME CLASS VALUE
>> ---------- ---------------------------------------------------------------

• ---------- ----------
  >> 129 background checkpoints started 8 253
  >> 130 background checkpoints completed 8 252
  >>
  >> 15m seems like an incredibly long time to be doing a checkpoint even for
  200M.
  >> I was under the impression that checkpoints should take seconds, not tens
  of
  >> minutes. There is no heavily used data on the disks with the redo logs and
  the
  >> disk array they're on should be blazingly fast. So I'm very frustrated
  that
  >> they seem to be very slow.
  >>
  >> And the redo logs do seem to be a bottleneck. When I select from
  >> v$session_wait I nearly always see at least one session and often two or
  more
  >> waiting on "log file sync". I'm worried this indicates a serious problem
  with
  >> the redo logs.
  >>
  >> --
  >> greg
  >