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RE: DBWR Mystery

From: Reddy, Gautam <>
Date: Thu, 7 Sep 2000 17:01:01 -0500
Message-Id: <>

This should clear you doubts.

kcbsdl -: When DBWR is posted to make free buffer, it scans up to N buffers in LRU list ( from TAIL to HEAD) looking for dirty buffer . To simplify, N is adjusted between kcbsdl and kcbsdh .

kcbscc -: DB writer checkpoint clump = percentage of write batch for low priority checkpoint request. When DBWR performs checkpoint, it tries to advance every pending checkpoint-request by writing buffers . For low priority checkpoint request, the total number of buffers that will be flushed is (kcbscc/100)*kcbswc

Let me know if I can be of more help.


-----Original Message-----
From: K Gopalakrishnan [] Sent: Thursday, August 31, 2000 3:47 AM
To: Multiple recipients of list ORACLE-L Subject: DBWR Mystery

Hi ..

I am getting confused with the following DBWR related TAGs .

 50 kcbswc DB writer IO clump
 16 kcbscc DB writer checkpoint clump
 13 kcbsdl DBWR blocks to scan lowest value  50 kcbsdh DBWR blocks to scan highest value   5 kcbsdi DBWR scan depth increment
 50 kcbsfs foreground blocks to scan looking for free 200 kcbnbh number buffer headers
247 kcbnbf number buffer objects

Total number of buffers =200 and the DBWR Write batch size is 50. (i.e IO Clump).. But there are two more otehr tags (kcbsfs and kcbsdh) are also 50. Does that mean DBWR will scan so buffers (kcbnbh/4) all the times whenever you need a free buffer in the hash chain. And what is the difference between kcbscc and kcbsfs.(both are kcbnbh/4 here).

And the other point of confusion here is the difference in checkpoint clump and IO clump. What parameter (or algorithm ) used in deciding the and kcbscc .

I am using Oracle 8.0.3 with no buffer pools configured if that matters.

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Author: K Gopalakrishnan

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Received on Thu Sep 07 2000 - 17:01:01 CDT

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