| SCN Mistery [message #51369] |
Sat, 18 May 2002 02:00  |
Thomas P Mathew
Messages: 2
Registered: May 2002
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Junior Member |
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Hi DBAs. Thanx in advance for a satisfactory reply for this question.
Are SCNs associated with all DMLs, whether committed or not, OR only for committed changes ?
One Oracle Press released book says that a unique SCN will be associated with each & every change made to the data blocks in the Buffer Cache & that a commit record will be identified by a commit SCN & those not committed will be rolled back later. Does this mean that there can be gap in SCN sequence ?
But another Oracle Press release specificly tells that SCNs are associated with only committed records. I fear that much material is not available in this aspect. Isn't this slightly fuzzy ? Any positive response welcome.
Rgds
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| Re: SCN Mistery [message #51389 is a reply to message #51369] |
Mon, 20 May 2002 19:37  |
Kishore
Messages: 45
Registered: September 2000
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Member |
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Hi,
No, the SCN will not be generated for any UNCOMMITTED transactions. Only COMMITTED changes generate SCN. The redo/archive files contains the information about the 'rollback information associated with uncommitted blocks/transactions also'. During the recovery, if it can not find an SCN (this is true for uncommitted ones) it rollback/undo the change associated with that block and keeps the old image back in place.
I hope this helps you,
Kishore
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