我在Oracle的metalink看到这么一段话。
When DB_BLOCK_CHECKSUM set to TRUE, what will happen when redo log corruption is detected?
I would like to set DB_BLOCK_CHECKSUM to TRUE to further protect the redo log files. What before this I would like to understand its behavior: When the checksum for one member of a redo log group is invalid, what will happen on archiving? When the checksums of all members of a redo log group are invalid, what will happen?
From: Brandon Cole 25-Apr-02 15:57
Subject: Re : When DB_BLOCK_CHECKSUM set to TRUE, what will happen when redo log corruption is detected?
It's been a while since I went over this stuff.
1. If LGWR can access at least one member in a group, the writing to the accessible members of the group proceeds as usual; LGWR ignores the unavailable members of the group. If the group was not active -- that is, the checkpoint was completed -- then dropping and adding a new redo log member solves the problem. Otherwise, you have to first force a log switch.
2. If all members of the next group are inaccessible to LGWR at a log switch, the instance shuts down. If the group was not active, then dropping and adding a new redo log group solves the problem. If not, the database may need media recovery from the loss of an online redo log file.
3. If all members of the current group suddenly become inaccessible to LGWR as they are being written, the db instance shuts down. In this case, the database my need recovery from the loss of an online redo log file.
Seemed I didn't express clearly enough. I was asking if redo log CHECKSUM mismatch occured when DB_BLOCK_CHECKSUM was enabled, how will Oracle act? The redo log is still accessable, only data corruption occurs. Without DB_BLOCK_CHECKSUM enabled, ARCH cannot detect this corruption and will archive as usual because redo log is still physically accessable. But when DB_BLOCK_CHECKSUM is enabled, will ARCH act differetly?
Tom answered partly that ARCH may report errors but will the redo log still be archived, when only one member is corrupted or all members are corrupted, respectively?
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