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What does latch explain? [message #289952] Wed, 26 December 2007 21:12 Go to next message
trantuananh24hg
Messages: 668
Registered: January 2007
Location: Ha Noi, Viet Nam
Senior Member
Hi all!

This is a brief of statspack report
Quote:


Total ----------------- % of Waits ------------------
Event Waits <1ms <2ms <4ms <8ms <16ms <32ms <=1s >1s
-------------------------- ----- ----- ----- ----- ----- ----- ----- ----- -----
latch free 429 7.0 3.0 8.2 8.9 13.5 22.4 26.3 10.7
latch: In memory undo latc 1 100.0
latch: cache buffers chain 287 32.8 6.3 4.5 13.2 7.0 4.9 31.4
latch: cache buffers lru c 4 100.0
latch: checkpoint queue la 1 100.0
latch: library cache 1806 24.3 15.2 15.0 10.9 8.0 8.5 14.7 3.5
latch: library cache lock 17 11.8 5.9 5.9 5.9 70.6
latch: object queue header 6 16.7 33.3 16.7 33.3
latch: parallel query allo 12 25.0 75.0
latch: redo allocation 3 33.3 33.3 33.3
latch: row cache objects 10 40.0 10.0 20.0 30.0
latch: session allocation 106 89.6 3.8 5.7 .9
latch: shared pool 1458 11.6 6.7 16.5 20.7 15.7 9.2 15.7 3.9



Please explain this brief of latch. I do not understand much, especially about <1ms ; <2ms ; <3ms ; <4ms ...

OS: Solaris 10
Database: 10.2.0

Thank you!
Re: What does latch explain? [message #289997 is a reply to message #289952] Thu, 27 December 2007 01:24 Go to previous messageGo to next message
Michel Cadot
Messages: 64153
Registered: March 2007
Location: Nanterre, France, http://...
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<1ms: percentage of waits that last less than 1ms
<2ms: percentage of waits that last 1ms and more but less than 2ms
<4ms: percentage of waits that last 2ms and more but less than 4ms
...

Next time use "code" and not "quote" tags to display listing.

Regards
Michel
Re: What does latch explain? [message #290000 is a reply to message #289997] Thu, 27 December 2007 01:31 Go to previous messageGo to next message
trantuananh24hg
Messages: 668
Registered: January 2007
Location: Ha Noi, Viet Nam
Senior Member
Thank you Michel!

Re: What does latch explain? [message #290007 is a reply to message #289952] Thu, 27 December 2007 01:52 Go to previous messageGo to next message
varu123
Messages: 754
Registered: October 2007
Senior Member
Whats the difference between a latch and lock?
Re: What does latch explain? [message #290011 is a reply to message #290007] Thu, 27 December 2007 01:59 Go to previous messageGo to next message
trantuananh24hg
Messages: 668
Registered: January 2007
Location: Ha Noi, Viet Nam
Senior Member
varu123 wrote on Thu, 27 December 2007 14:52

Whats the difference between a latch and lock?


Is it a question requiring an explanation or any guide document?
Re: What does latch explain? [message #290014 is a reply to message #290007] Thu, 27 December 2007 02:07 Go to previous messageGo to next message
Michel Cadot
Messages: 64153
Registered: March 2007
Location: Nanterre, France, http://...
Senior Member
Account Moderator
Quote:

Whats the difference between a latch and lock?

Database Concepts
Part III Oracle Database Features
Chapter 13 Data Concurrency and Consistency
Section How Oracle Locks Data

Regards
Michel
Re: What does latch explain? [message #290018 is a reply to message #289952] Thu, 27 December 2007 02:54 Go to previous message
halfydba
Messages: 20
Registered: November 2007
Location: Australia
Junior Member
Simplest way to remember what each is:- Latch is for memory. Lock is for Data. So you have row locks, but memory latches.

In 10g there is a new mechanism called a mutex, which is similar to a latch but (in simple terms) blocks less than a latch.
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