Why the latches is if the mutex are better?

Hi all

I'm trying to understand the mutex and latches, also searched the forum and read other messages.

My question is, almost in each paper said: mutex are faster, less false assertion, less size etc... also are locking latches a block of memory, but each object has its own mutex.

two of them are nice locking mechanism, which is OK but if the mutex are better why latches are exist? What is advantages of locks?

Mustafa KALAYCI says:
Aman,

I'm really starting to feel like a fool. each different answer changing my understanding of locks and mutexes.

Isn't fun?

When started this topic, I thought that the clasp and mutexes are both a locking mechanism that during a process of reading in or by writing to something a piece of memory, process locked this field and make it's own, it's lock is a lock, or mutex (it is also very close to description of University oracle performance tuning training manuals).

In this book, its very clearly explained that latches may present a statement false . For example, when you see a Cache library top 5 events, you should interpret, this is a good thing or a bad thing? Without access to it, you can't search for the library Cache hash strings and cannot come to know that the slider required on your part is there or not? That means, until the moment that you do not have the hand on Library Cache, the decision to go for a hard or soft analysis is not possible and that is waiting for the library Cache lock, is of no real use at all. This is a false assertion and Mutex can help minimize this. Good read this page completely and with a little more attention and you need to understand.

then I started to know the difference between the lock and the mutex. at first, I thought that HLDAA and mutex concepts belong to the oracle database, but I realized I was wrong. It is a technique of joint programming for shared resources.

This isn't a concept of programming but the mechanism for the protection of the integrity of the structures of memory.

I'm not sure that the lock concept is nowhere else or not in addition to oracle. But the notion of Mutex is already there in the operating system concepts.
http://en.Wikipedia.org/wiki/Mutual_exclusion

documents almost I read told me that mutex are just better and I'm just curious, if mutexes are better, why are locks used.

I mentioned several times the answer to this, the concept of lock is a proven concept and is around for many years in oracle. Simply because the Mutex is better, this does not mean that Oracle, the next day, everything would change and will begin to deploy the mutex. You realize that Oracle code isn't just 10-15 lines that its really possible to change in a short way.

When I run a query, first oracle will search this library if cached query cursor can not found create it there and then start interviewing research data. While the oracle process research to the cursor when it exists, it crashes a block of memory that it is currently reading in the library cache. After that, he will start looking to the data buffer cache. in seeking the data block, each block will be locked again while reading process and released when he finished reading.

in which level a mutex and latch will be created and released. It might be easier if I get an example like that.

for the moment, I think that mutexes and locks are algorithms to protect the wrong again... maybe shared structure.

They are different ways to do the same thing, latches are something you need to wait, revolve around the CPU to get their hands on them. Mutex, are much faster, can be acquired more quickly and released more quickly as well.

HTH
Aman...

Tags: Database

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