RE: Log file synch / direct path writes

Don't forget,

LGWR also flushes the buffer every 3 seconds. Think about your transaction rate and whether you will make use of a large buffer space.

My $0.02,
Andy.

-- 
Andrew Sit
Systems Engineer
DataMirror Corporation 
+ 1 905 415 0310 (O)
+ 1 416 839 9908 (M)

-----Original Message-----
Sent: Monday, June 24, 2002 2:19 PM
To: Multiple recipients of list ORACLE-L



Ramon,

For one thing, LGWR will write the log buffer when it is 1/3 full, or if
it reaches 1MB.  So, its useless to have the log buffer more than 3MB.
The space beyond 3MB could never possibly be used.  

My .02

Beth

-----Original Message-----
Sent: Monday, June 24, 2002 1:28 PM
To: Multiple recipients of list ORACLE-L


Jared,

Just to clear my thoughts, doubts and keep learning from the list.

What implications can cause having a big log buffer.

As I can remember, LGWR copy data from the log buffer to the redo logs
when
log buffer is 1/3 full, timeout, commit and a few more.

So it will fire when the first one occurs, base on that theory, what
matters
if the log buffer is 1mb, 10mb, 100mb.  Anyway LGWR will copy the data
to
the redo logs.

I had some problems of performance the last week and some of you got
surprised because I had a log buffer of 100MB.

I have never read some documentation, obviously have to read more and I
am
doing it believe me, that tells not to do it.

I would like some comentaries or your considerations about this,

TIA

Ramon


----- Original Message -----
To: "Multiple recipients of list ORACLE-L" <ORACLE-L_at_fatcity.com>
Sent: Saturday, June 22, 2002 1:33 PM




>

> Just how large is your overly large log buffer?

>

> 10 meg?

>

> 100 meg?

>

> 1 Gig???  ( ok, I've never heard of one this big,

> but you never know ;)

>

> Jared

>

> On Friday 21 June 2002 12:48, Erik Williams wrote:

> > I have an instance that is waiting on log file synchs. I suspect

that
the


> > waits are a result of a overly large redo log buffer. There are also

> > considerable waits on direct path writes. The redo logs are on

QuickIO,
so


> > I assume that the writes LGWR is writing asynchronously and not a

source
of


> > the log file synchs. I want to be sure that the log file synchs and

direct


> > path writes are not related before I begin to experiment with the

size
of


> > the redo log buffer. How can I be sure that the waits are being

caused
by


> > DBWR and not LGWR? What are possible fixes for the direct path

writes if
it


> > is the DBWR causing them? Multiple DBWR? The datafiles are not on

QuickIO,


> > just the redo.

> >

> > Thanks

> > Erik

> --

> Please see the official ORACLE-L FAQ: http://www.orafaq.com

> --

> Author: Jared Still

>   INET: jkstill_at_cybcon.com

>

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