Oracle Core Technology notes (this book is not carefully read, so you need to read it later ~~), Oracle Core Technology

Oracle Core Technology notes (this book is not carefully read, so you need to read it later ~~), Oracle Core Technology
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Directory Start 1 2redo and undo 3. Transactions and consistency 4. locks and latches 5 cache and copy 6. Write and restore 7. Analysis and Optimization 8RAC and 'defect' 9 appendix A dump and debugging

Start redo and undo

• The actual order is 3 1 2 4 4, 2 redo logs are merged into one log record and written to the redo buffer.
• The first modification in the transaction contains some special steps *
• (My summary) theoretically, if the redo log is successfully written, it means that the transaction has been successfully committed. If the database crashes and the current status in the memory is not updated to the database storage, the redo operation can be performed to ensure the completion of the transaction. On the other hand, the failure of a nested transaction causes the database update to be rolled back. In this case, undo is required, however, the undo itself may be lost due to the crash of the storage in the volatile region. In this case, you need to use the undo redo log to restore the dataPrevious consistent status

  From the above description, we can see that the transaction implementation depends on the data modification which is reversible. Otherwise, the state will be easy to lose (such as value assignment and file write operations ). Consistent recovery

  Consistency recovery depends on the creation of global consistency snapshots (MVCC). Therefore, the special underlying attributes such as the transaction ID and timestamp are required. Refer to the related concepts in CLojure language.

Why?The undo record prevents other users from viewing the data that we are changing (intermediate temporary status)

Redo allocation latch: protects the redo log buffer (because only one lgwr performs serial write operations)

P17 everyone is doing a little "extra" work (collaboration overhead ?), It means they can work in different places at the same time, without having to compete in the same place frequently (contention)

Redo simplicity

Undo complexity

Transactions and consistency

Transactions and undo

X $ ktuxe

Newing, & flash back...

A single undo block can contain the undo records of multiple transactions

Data block access and undo

Submit SCN

Large Object (LOB)

Summary

Locks and latches

Wait for the wake-up mechanism (equivalent to the semaphore in the Linux kernel ?)

Library cache latch

Lock: Protection object (Lock = queue ?)

Deadlock

Lock mode

Locks *

KGL lock (and pin)

The lock and pin => 11G are gradually replaced by Mutex.

Cache and Replication

Multiple Data Block caches

Working Set

LRU/TCH Algorithm

REPL_AUX

Search for Data

Write and recovery

Dbwr

Write process interaction

Restore

Analysis and Optimization of RAC and "defect" Appendix A dumping and debugging