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Among the failure events, which is the most serious and may cause data loss? A. The loss of an entire redo log-file
group but no loss in any other group
--- Explanation: Among the given failure events, we're asked to identify which is the most serious and could cause data loss. Let's go through each option one by one. Option A states that the loss of an entire redo log-file group could cause data loss. To understand this, we need to first understand what a redo log-file group is. In Oracle Database, a redo log-file group is a set of two or more redo log files that Oracle Database writes to sequentially. The purpose of these files is to record all changes made to the database, so that in case of a failure, these changes can be recovered. Now, if an entire redo log-file group is lost, it means that all the redo log files in that group are lost. This is a serious issue because any committed transactions that were not yet written to the database files may also be lost, resulting in data loss. Option B states that the loss of one member of each redo log-file group does not affect database operation and does not result in data loss. This is because, as I mentioned earlier, a redo log-file group consists of multiple files. So, even if one file is lost, the database can still function properly using the other files in the group. Option C talks about the failure of the ARCn background process. ARCn stands for Automatic Recovery Coordinator, and it is a background process that performs crash recovery for standby databases. If this process fails, Oracle Database spawns another one, so there is no data loss. Option D talks about the failure of the LGWR background process. LGWR stands for Log Writer, and it is a background process that writes redo log entries to the redo log files. If this process fails, it causes an instance failure, but you do not lose any committed transaction data. This is because LGWR writes redo log entries in a circular fashion, so any committed transactions are already written to the redo log files before LGWR fails. So, based on this information, we can conclude that option A is the most serious and could cause data loss. In contrast, options B, C, and D do not result in data loss.
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