This is a reference note for the wait event "log file sync" which includes the following subsections:
Definition:
Individual Waits:Parameters:
Wait Time:等待时间The wait is entirely dependent on LGWR to write out the necessary redo blocks and confirm completion back to the user session. The wait time includes the writing of the log buffer and the post. The waiter times out and increments the sequence number every second while waiting.这种等待完全依赖于LGWR写出所有必要的redo块,确保完成后返回给用户session。等待时间包括了日志缓冲写操作和提交操作。等待的时候,每秒都会增加序列号。 Finding Blockers:查找阻塞的块If a session continues to wait on the the same buffer# then the SEQ# column of <> should increment every second. If not then the local session has a problem with wait event timeouts. If the SEQ# column is incrementing then the blocking process is the LGWR process. Check to see what LGWR is waiting on as it may be stuck.如果一个session持续等待同一个buffer#,那么SEQ#列应该每秒都会增加。否则本地session会出现等待事件超时的问题。如果SEQ#列持续增长,那么阻塞进程就是LGWR进程。检查LGWR正在等待哪些日志块的完成而被卡住。 Systemwide Waits: 系统级等待Systemwide figures for waits on "log file sync" show the time spent waiting for COMMITs to complete. If this is significant then there may be a problem with LGWR's ability to flush redo out quickly enough. One can also look at:系统级”log file sync“的等待参数显示了等待COMMIT完成花费的时间。如果这种等待非常明显,那么LGWR快速完整地刷出redo的能力就有问题。这一点还可以看:LGWR的"log file parallel write"等待(见Note:34583.1)和 ”user commits“统计数据显示COMMIT的次数。 Reducing Waits / Wait times: 减少等待/等待时间
Data Guard Perspective: Data Guard的观点For Data Guard with synchronous (SYNC) transport and commit WAIT defaults, the above tuning steps still apply, except step 3 also includes the time for the network write and the RFS/redo write to the standby redo logs.对于Data Guard,具有异步传输与默认的COMMIT WAIT功能,以上的调优步骤仍可以使用,除了第三步也包括对于备机redo日志的网络写与RFS/redo写的用时。 You can restrict the list below to issues likely to affect one of the following versions by clicking the relevant button:
Related:REFERENCESNOTE:7452373.8 - Bug 7452373 - "log file sync" timeout is not configurableNOTE:7568734.8 - Bug 7568734 - AIX: Sporadic spikes of 'log file sync' on AIX with heavy commit concurrency NOTE:7610362.8 - Bug 7610362 - Long "log file sync" waits in RAC with broadcast on commit in RAC NOTE:7643632.8 - Bug 7643632 - High log file sync in Data Guard maximum availability (sync) mode NOTE:7716356.8 - Bug 7716356 - Long "log file sync" latencies with broadcast on commit scheme in RAC NOTE:8220734.8 - Bug 8220734 - Long "log file sync" wait in RAC NOTE:8490879.8 - Bug 8490879 - Long "log file sync" latencies due to broadcast on commit scheme NOTE:9095696.8 - Bug 9095696 - "log file sync" wait time spikes with ARCHIVE_LAG_TARGET set NOTE:9776431.8 - Bug 9776431 - 11.1.0.7.3 fix for 8220734 is incomplete - "log file sync" timeout set to 1 second NOTE:2640686.8 - Bug 2640686 - Long waits for "log file sync" with broadcast SCN in RAC NOTE:2663122.8 - Bug 2663122 - Unneccessarily long waits on "log file sync" can occur NOTE:12378147.8 - Bug 12378147 - Long broadcast ack warning messages, and/or many Log File Sync timeouts in foregrounds in RAC NOTE:13074706.8 - Bug 13074706 - Long "log file sync" waits in RAC not correlated with slow writes NOTE:5087592.8 - Bug 5087592 - "log file sync" waits from read only commits NOTE:5896963.8 - Bug 5896963 - High LGWR CPU and longer "log file sync" with fix for bug 5065930 NOTE:5147386.8 - Bug 5147386 - Long waits on "log file sync" /random ORA-27152 "attempt to post process failed" NOTE:6193945.8 - Bug 6193945 - High LGWR CPU use and long 'log file sync' latency in RAC NOTE:61998.1 - Introduction to Tuning Oracle7 / Oracle8 / 8i / 9i NOTE:6319685.8 - Bug 6319685 - LGWR posts do not scale on some platforms NOTE:3311210.8 - Bug 3311210 - Unnecessary 0.5 seconds waits for "Broadcast on commit" SCN scheme NOTE:34583.1 - WAITEVENT: "log file parallel write" Reference Note NOTE:387174.1 - MAA - Data Guard Redo Transport and Network Best Practices NOTE:5061068.8 - Bug 5061068 - RAC using "broadcast on commit" can see delayed commit times NOTE:5065930.8 - Bug 5065930 - "log file sync" timeouts can occur |
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