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Re: CHECKPOINTS

From: Mario <mtechera_at_yahoo.com>
Date: 2000/03/02
Message-ID: <89lcvk$lnc$1@news.online.de>#1/1

Hi Steve,

AIX Version 4.3

Total physical disks for data files is 3 (note that they are mirrored
amongst each other).

As for the AIO, it is available.

There are 24 data files
(the system TS 2,
rollback segs 6 files,
temporary TS 2,
projects TS 9,
projects indexes TS 5)

USE_ASYNC_IO = TRUE

DB_WRITERS=0
DB_FILES=200
DB_FILE_SIMULTANEOUS_WRITES=4

_DB_BLOCK_WRITE_BATCH= NOT SET
DB_BLOCK_CHECKPOINT_BATCH=64
DB_BLOCK_BUFFERS=32000
DB_BLOCK_SIZE=8192

We are using a set of 10 relog groups.
Each at 50MB each, i.e. 500 MB
redo log space. Why are jobs writing
so much to the redo logs? Are the
rollback segs being logged?

Any help is welcome.

Thanks,
Mario

Steve Adams <steve.adams_at_ixora.com.au> wrote in message news:38bde49d.37255270_at_news.eagles.bbs.net.au...
> Hi Mario,
>
> This is a DBWn bottleneck.
> Some questions ...
>
> What version of AIX?
> Is aio available (it should be)?
> To find out, do the following as root
> # smit aio
> select "Change/Show Characteristics of Asynchronous I/O"
> How many datafiles do you have?
> How many physical disks (spindles) underlying the data files (not
> counting log files)?
> What are the values of the following parameters?
> use_async_io
> db_writers
> db_files
> db_file_simultaneous_writes
> _db_block_write_batch (if set)
> db_block_checkpoint_batch
> db_block_buffers
> db_block_size
>
> Regards,
> Steve Adams
> http://www.ixora.com.au/
> http://www.oreilly.com/catalog/orinternals/
> http://www.christianity.net.au/
>
>
> On Wed, 1 Mar 2000 23:12:32 +0100, "Mario" <mtechera_at_yahoo.com> wrote:
>
> >
> >We have a problem with redo log switching
> >when running large jobs. All groups fill up
> >and remain active even though they
> >are archived - presumably this is because
> >checkpointing is going on.
> >
> >Finally when the
> >last log group fills and wants to switch back to
> >the first group it cannot do so, because
> >the first group is still active. At this point the system
> >slows to a crawl and even trivial queries require minutes
> >for a response.
> >
> >We have
> >increased the number of redo log groups
> >(almost doubling the space available),
> >and have also increased the initialization
> >parameter db_block_checkpoint_batch
> >so as to allow for faster checkpointing.
> >Yet the problem persists.
> >
> >Does anyone have any pointers for us?
> >
> >Is there any good documentation on how the checkpoint
> >process works and why it takes so long?
> >
> >Our System
> >Oracle V7.3.4, RS/6000, 2CPUs, 1.3 GB Memory, AIX
> >
> >Thanks in advance,
> >Mario
> >
> >
> >
> >
>
Received on Thu Mar 02 2000 - 00:00:00 CST

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