RAC中的global cache cr request等待事件 过长

shahand

完全支持rollingpig

shahand

心跳网络最好用千兆或者更好的配置

千兆现在也花不了多少钱，网卡好像2、3百，switch好像也在1k以内。

wa0362

充分说明：
rac环境中，client连接的时候也要根据业务不同而固定连接到固定节点上

stacyruirui

Yong Huang,

I think when the ratio is larger than 25%,  _fairmess_threshold should be reduced.  

In addition, I think to check interconnection and lms process first.  If there are gc cr failure and gc block/grant congested event in statpack report,  those problems should be fixed first.

stacyruirui

原帖由 Yong Huang 于 2007-11-28 02:52 发表
It makes me think of the parameter _serial_direct_read (enable direct read in serial). Once you set it, all db file scans that cause db file scattered read wait, such as FTS or index fast full scan, will bypass buffer cache, and the wait event changes to direct path read. You want to avoid polluting buffer cache by FTS. Right? That's the parameter you can try. Even alter session works.

Yong Huang

Is the parameter helpful?  cr request event is caused by remote cache access to old image or remote instance undo block.

stacyruirui

原帖由 zhu47172310 于 2007-2-2 13:41 发表
不好意思，dump ipc我不会。本人人比较懒，目前系统正常在用，不想在搞什么事，没有深入研究，就撮合着用吧。

dump ipc 不需要 shutdown db

SQL> oradebug setmypid
Statement processed.
SQL> oradebug ipc
Information written to trace file.
SQL> oradebug tracefile_name

Find keyword "info for network"

wbnqnx

原帖由 biti_rainy 于 2007-11-27 19:41 发表
两个可能因素造成
1： 节点之间interconnect 通讯 的 global CR
2： 本节点索引访问造成block cache离散，增加了io量

这样一个fts 导致io增加和global cr ，可能会造成情况恶化。

BTW: 即使单节点数据库，原因2 也可能导致fts 很慢，data buffer偏大可能造成情况更糟糕，因为io 大大增加。

data buffer偏大可能造成情况更糟糕，因为io 大大增加。

这个是什么意思，不懂。。。。

Yong Huang

原帖由 stacyruirui 于 2008-1-7 23:40 发表

Is the parameter helpful?  cr request event is caused by remote cache access to old image or remote instance undo block.

I'm not sure if setting _serial_direct_read to true helps reduce global cache cr requests. But in theory, it should work. It basically changes your RAC database to behave like a non-cache-fusion database, temporarily for that type of scan. That is, when a block is needed (for scattered read only; note the word "scattered" here corresponds to "serial" in "_serial_direct_read"), Oracle doesn't bother to check buffer cache; instead the process directly goes to disk and reads. If that's the case, global cr requests should drop.

On the other hand, you may ask: Whenever a direct read is needed, it's always preceded by writing dirty buffers for the needed blocks to disk first. So the *old* blocks for this segment in global buffer cache have to be scanned anyway. So we don't gain anything. Is that why you're asking?

So, I actually don't know. Somebody else may have more insight, and possibly come up with a good experiment to prove the effectiveness or lack of. I would appreciate that.

Yong Huang

lsq_008

学习一下老帖子

huanhuanlove

good  今天看一个internal的文档 刚好描述了该隐藏参数
_fairness_threshold

--------------------------------------------------------------------------------
NOTE: This is an internal Oracle parameter. Do NOT use it unless instructed to do so by Oracle Support. Playing with this parameter may be harmful.
Oracle 11.1.0:
Parameter Name: _fairness_threshold  
Description: number of times to CR serve before downgrading lock  
Type: NUMBER  Obsoleted: FALSE  
Can ALTER SESSION: FALSE  Can ALTER SYSTEM: IMMEDIATE  

Oracle 10.2.0:
Parameter Name: _fairness_threshold  
Description: number of times to CR serve before downgrading lock  
Type: NUMBER  Obsoleted: FALSE  
Can ALTER SESSION: FALSE  Can ALTER SYSTEM: IMMEDIATE  

Oracle 10.1.0:
Parameter Name: _fairness_threshold  
Description: number of times to CR serve before downgrading lock (DFS)  
Type: NUMBER  Obsoleted: FALSE  
Can ALTER SESSION: FALSE  Can ALTER SYSTEM: IMMEDIATE  

Oracle 9.2.0:
Parameter Name: _fairness_threshold  
Description: number of times to CR serve before downgrading lock (DFS)  
Type: NUMBER  Obsoleted: FALSE  
Can ALTER SESSION: FALSE  Can ALTER SYSTEM: IMMEDIATE  

Oracle 8.1.7:
Parameter Name: _fairness_threshold  
Description: number of times to CR serve before downgrading lock (DFS)  
Type: NUMBER  Obsoleted: FALSE  
Can ALTER SESSION: FALSE  Can ALTER SYSTEM: IMMEDIATE