Re: DBWR Question

Hi Tarig !

I guess you are using the tool TOAD (or something from Quest Corp . Right??). Well.

When oracle reads data from disk, it has to keep that in data base buffer cache subject to avaialble free space in the buffer cache. While searching for free buffers in buffer cache, if it doesn't find a free buffer it waits for 'free buffer waits'.

The number of buffers scanned , when there is a need for free buffers is called DBWR avg scan depth. The internal write batch size of DBWR is a function of # of datafiles and so is the recommendation.

Database writer internal write batch size which is set to the lowest of the following three values (A, B, or C):

Value A is calculated as follows:
DB_FILES*DB_FILE_SIMULTANEOUS_WRITES/2 Value B is the port-specific limit.

Value C is one-fourth the value of DB_BLOCK_BUFFERS.

In Oracle 7.3 and 8.0 the internal write batch size is calculated using the above algorithm and in 8i it is fixed in the code.

K Gopalakrishnan
Bangalore, INDIA
http://www.gopalakrishnan.org

At 10:28 AM 6/28/00 -0800, Salih, Tarig - ASPEN Project wrote:
>Hi Gurus,
>
>What is DBWR avg Scan Depth?
>What is DBWR avg buffers scanned?
>If those values are too high, I get a recommendation that DB_FILES is too
>high. What is the relation between
>DB_FILES and DBWR avg Scan Depth and DBWR avg buffers scanned?
>
>Thanks in advance
>Tarig E .Salih
Received on Fri Jun 30 2000 - 09:21:33 CDT