Oracle動態效能檢視學習筆記(8)_v$waitstat

gdutllf2006發表於2010-07-26
Oracle筆記AI
Oracle動態效能檢視學習筆記(8)_v$waitstat

目錄

參考文件<>Chapter 24


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1 Overview
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This view keeps a summary all buffer waits since instance startup. It is useful for breaking
downing the waits by class if you see a large number of buffer busy waits on the system.

描述關於Buffer Waits的資訊。

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2 Userful Columns for v$session
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1) Class: Class of block(data segment header, undo segment header, data block)
在Buffer Cache中的資料塊型別就只有這三種？？
不是的
select distinct class from v$waitstat;


2) Waits: Number of waits for this class of blocks.

3) Time: Total time waited for this class of block


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3 Reason for waits 出現Buffer Cache等待的原因
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1) Undo Segment header: not enough rollback segments

2) Data segment header/freelist: freelist contention

3) Data block

4) Large number of CR clones for the buffer

5) Range scan on indexes with large number of deletions.

6) Full table scans on tables with large number of deleted rows

7) Blocks with high concurrency

(什麼時候會出現這現象呢？如何來模擬測試呢？)
需要結合等待事件來進一步學習。

來自 “ ITPUB部落格 ” ，連結：http://blog.itpub.net/10248702/viewspace-669519/，如需轉載，請註明出處，否則將追究法律責任。

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