Picked Lamport scheme to generate SCNs,lamportscns
故障現象:
資料庫節點1由於卡死重啟後,資料庫執行個體無法open,警告日誌沒有錯誤只有一條記錄:Picked Lamport scheme to generate SCNs,節點2正常,應用可以正常使用。
分析處理:
1 檢查資料庫系統的警告日誌包括節點1:alert_szm21.log,節點2:alert_szm22.log,沒有報錯現象。
2 節點1資料庫執行個體: oradubug dump systemstate 10 oradebug analyze 3,ass109.awk分析沒有等待和死結現象。
3 metlink上對Picked Lamport scheme to generate SCNs的理解分析發現
Lamport 10.1 前:
Commit Broadcas 10.2後:
系統有如下問題的時候應該scn推薦Commit:(文檔 ID 259454.1
However, if any of the following conditions exist, there may be a need to
deviate from the default and explicitly set max_commit_propagation_delay=0.
- The data consistency between the different instances must be guaranteed and
immediate i.e. if commits must be seen instantaneously on remote instances.
- When rapid inserts (or updates) and immediate queries of the same dataset are
done from different instances.
- If middle-tier connection pools are being used in tandem with connection load
balancing to the RAC instances, and the application is arbitrarily selecting a
connection (and hence an instance) for each SQL operation.
- Some packaged applications (e.g. SAP) might recommend setting this parameter
to a specific value (mostly 0), in which case you should follow the
application vendor’s recommendations.
SCN演算法上10.1前的版本與10.2的版本有明顯不同,老版本演算法存在不足的地方,
通過以上三條分析:決定對節點1進行重新啟動,或許重現問題或許解決問題:重新啟動節點1後,執行個體可以正常啟動。
總結:對與該類問題,通過各種手段沒有發現錯誤資訊,而且存在版本差異,重啟一般可以解決問題,
有其他思路請留言!!