Can someone help me understand the process Instance recovery

First thanks for all of you who responded to my post, any help is really appreciated.

I would like to more deeply understand the Instance recovery process then the Administration Guide of Oracle Docs can tell me.

What I have so far of Instance recovery is:

1 oracle determines which files are not synchronized.
2. all data from redo log files is applied to restore log buffers by progression. Buffers do not participate on the database of normal transactions because they are marked to pick it up.
All these data are applied to the data files (commited and contains transactions).
This step is called roll forward.
3 cancellation are used to restore transaction no. After this step the datafiles not aura no data contains on them. At this point, the instance is available for users, but the blocks used are not.
4. all files are now in sync.

My questions are:

-Step 1, what process determines which files are not sync? Make the bed of Smon the controlfile and data file headers and then make a list which is not sync?

-L' step 2, what is the process that reads the information in the redo log files and complete the recovery log buffer? What is the CKPT? And how he is warned that he might start to read the files after completing step 1? There is a semaphore that is defined for it?

-Step 2, which process applies information engaged and contains buffer redo log for the data files? When it starts to apply this information of the instance is already partially available to users?

-Step 3, what is the process that reads up to cancel to restore transactions not? This process must be done once step 2 is complete as could be blocks of the undo tablespace on buffers of the right-wing newspaper do it again? And when this step 3 starts, the process is triggered by an another semaphore?

-When step 3 is finished, what process changes the State of the database of partially open to open, or that's just what we call it when the database has always revenge marked for recovery?

Thanks again in advance for the help, there are reasons not practice known this information, I'm just a curious person who could not find this information on the google...


Ricardo Rodriguez

Ricardo,
Well, I'll take a chance to respond.
(1) SMON in the start-up phase, in the strict sense in the editing phase, compares the SNA stored in the control file with the data file headers. This sCN is called checkpoint SCN. It is always higher among the controlfile so its part of the same database and is not set up to an old backup. By this correspondence, Oralce comes to know that there are some report files with their SNA control point is only not with the controlfile and consequently, instance recovery is reported. Here is the list of files is prepared.
(2) the same process SMON only would trigger playback of the redo log files and launch the Rollforward process. Roll forward is made from the last address bytes redo controlled at the end of the restore log forward. This means that the last block, blocks have not reported in the data file are simply read and are dumped on the data files. As a result, we get a situation that the data file will end up with a lot of data committed but also committed that redo is containing both.
CKPT process will not come in the picture I think. Where did you read what CKPT would do all this?
(3) SMON governs all this thing is to say the application of the data for the data files. No, in this phase, we are still in the phase of mounting that this recovery is called crash recovery. Oracle wouldn't let users to use the database at this point. Data is still not available for them.
(4) do not bring semaphores here. They are already in use when you allocated the memory of your instnace. Its work process level. After the mount phase is completed, oracle would open up the db. At this stage, "the transaction recovery" aka rear roller phase. That would be launched to relax all the operations that are not validated.
Now to do this, undo will be used. Oracle launches this phase into two or more strictly speaking 3 ways. One, SMON would just check how many blocks will be there for the recovery. If they are larger, it would begin the rear roller with parallel slaves. This is called "we demand" rollback. It is initiated by the user. So if you were using the EMP table data and the server crashed between, now the next time you start, if you try to access the same blocks once again, they are set aside on the basis of priority.
The third one will rollback transaction intra. It's basically splitting the work among the slaves so that if a slave is sitting free, it can share the work and can move forward to make things more quickly restored.
Please note that all this is happening at the open stage. This means then that this is the case, oracle is available for users. And second, there is little change in this process (an integer) 9i go. This is called two-pass recovery which has been made to make this process a little faster. In this regard, SMON ignores these blocks that are controlled by DBWR during execution of the phase of rollforward.
Hope this makes some sense and helps. Let me know if there is something wrong or unclear.
HTH
Aman...

Tags: Database

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