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中吴南顾惟一笑

成功法则就是那19个字

 
 
 

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MMDB:Log&Recovery   

2009-09-17 14:27:50|  分类: dbms |  标签: |举报 |字号 订阅

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Repeat history
Low Amount of disk I/O
    - Redo logs are written to disk
    - No undo logs to disk normally
Ping-Pong Checkpointing Scheme
    - Write to alternate disk copies on successive checkpoints
            resilient to crashes during checkpointing
Only relevant undo logs written to disk when checkpointing
    - undo logs of transactions that are active at the end of the checkpoint
Fuzzy checkpoints
    - Updates execute concurrently with checkpoints
            e.g. No page latching during checkpoints
    - Only dirty pages written to disk during checkpoints
Single pass recovery algorithm

Do not write logs for index.
    - If crash occurs, the index will be rebuild


Extended Logging Support:

Logging support for high concurrency
    - Multi-level logging
            Physical undo during updates, logical undo afterward
    - Post-commit actions
            Actions that cannot be rolled back (e.g. freeing storage space)
Support for user-defined operation logging
Time stamp recovery
    - Recover the database to a transaction-consistent point in the past
Turn redo logging off
    - Support atomic transactions without requiring them to be durable
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