Top event log file sync

Disk throughput is only one aspect that affects LGWR. It consumes CPU while executing too. If you've maxed out your CPU capacity processing "business transactions", then it will be starved for resource. This can lead to you seeing a lot of " log file sync " waits. If your datafiles are on the same disks as the redo logs, then DBWR will also be contending for the same disk. I had checked the CPU usage. Hello Muthu I am really not sure what problem you are trying to address here?

Are you trying to tune that concurrent request? Since there are 5 requests running, all of them may be generating much redo. Is this a custom program or standard seeded program? Is there a possibility of reducing redo size by dropping few indices on that table and then rebuild them later? Look for the opportunities to tune them.

Also, all these inserts, are they inserts with bind variables? Sorry to ask you more questions, but I would like to understand the root cause before giving you some suggestions. Thanks for the quick update. This is the standard Oracle report Journal Entries Report. Since this is not a real production, I think, we can think about it. Ours is a JFS2 type of file system. Hello Muthu Sorry, it took a while to respond.

Do you have tkprof for this report run? Is the parent job slow or report is slow? There have been many performance issues reported for journal entries report.

Bug fix was to truncate that table instead of delete. Bug I guess, we will have to look at tkrpof output files to see where the slowness. If you are trying to tune the instance for log file sync issues, I guess, converting delete statement to truncate statement might help.

Great article, thanks. Here is a small example from a Solaris VM. Analysis Period ————— AWR snapshot range from to Time period starts at MAR Database version Activity During the Analysis Period ———————————— Total database time was seconds. The average number of active sessions was Findings and Recommendations —————————-. Finding 1: Commits and Rollbacks Impact is Recommendation 1: Host Configuration Estimated benefit is Rationale The average size of writes to the online redo log files was K and the average time per write was milliseconds.

Impact is You might also need to increase the number of disks for better performance. The average response time for single block reads was 89 milliseconds. Recommendation 2: Host Configuration Estimated benefit is 2. If striping all files using the SAME methodology is not possible, consider striping these file over multiple disks. Finding 3: Undersized Buffer Cache Impact is 3. Recommendation 1: Database Configuration Estimated benefit is.

Recommendation 1: Segment Tuning Estimated benefit is. Related Object Database object with ID Additional Information ———————-. CPU was not a bottleneck for the instance. Session connect and disconnect calls were not consuming significant database time. Hard parsing of SQL statements was not consuming significant database time. LGWR process parallel write to both members at same time? Example: Say Group1 having two members multiplexing.

If not, LGWR will execute write system calls in succession. And, Yes, writes to both members must complete before the commit is declared successful. The application is several perl processes processing incomming messages on several message queues.

There is 4 perl processes per queue polling every 10 ms average of every 2,5 ms. The response time requirement is ms, but we see log file sync waits in trace above ms:.

The Oracle documentation writes: background elapsed time: Amount of elapsed time in microseconds consumed by database background processes. Is your log file sync wait time consistently that high? Also, check LGWR trace file to see if the feature adaptive log file sync is in play.

I have seen numbers not adding up due to various rounding issues with the statistics. In your case, 1second seems to be causing the rounding issues. Can you increase the time window to 10 seconds to see if you can eliminate rounding errors? Your site offered us with valuable info to work on. Hi superb website! Does running a blog like this require a lot of work? Anyways, if you have any recommendations or tips for new blog owners please share.

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Great article. Database was almost hung and application users not able to process. All were started to complaining about performance issues. At the same time I could see enq cf contention waits on insert query. I know its due to excessive commit causes the log file sync and high CPU utilization. Could you suggest me what is the temporary fix to run the application stable?

To view different time ranges or dimensions, use Azure Monitor. On the Windows Server that has the Azure File Sync agent installed, you can view the health of the server endpoints on that server using the event logs and performance counters. Use the Telemetry event log on the server to monitor registered server, sync, and cloud tiering health. Event ID is logged once a sync session completes. For more information, see the sync health and per-item errors documentation.

Sometimes sync sessions fail overall or have a non-zero PerItemErrorCount. However, they still make forward progress, and some files sync successfully. These fields tell you how much of the session succeeded. If you see multiple sync sessions fail in a row, and they have an increasing Applied count, give sync time to try again before you open a support ticket.

Event ID is logged for each per-item error once the sync session completes. Use this event to determine the number of files that are failing to sync with this error PersistentCount and TransientCount.

Persistent per-item errors should be investigated, see How do I see if there are specific files or folders that are not syncing? As a result during the peak activity period, the main wait event is log file sync. Given that I can't change these two things easily [i.

Thanks bipul. June 01, - am UTC. Sorry, the only ways to reduce log file syncs are a don't commit until your transaction is actually done. I thought so bipul, June 01, - pm UTC. Thanks for the reply. I knew there was no other way, but wanted your expert advice. Regarding: "transaction actually done", the transaction is actually done. This software is used to send emails to a mailing list. And it inserts and update data in 2 tables after sending each email.

No concpet of bulk operation! I might be able to do something about "securely bind both feet together".

We are changing our storage system and I think thats right time to sort this redo log on RAID-5 issue. What kind of RAID configuration would you suggest for redo log files?

June 01, - pm UTC. Thanks so much for your help. June 08, - am UTC. Hi Tom, Looking through wait events in Appendix A of reference manual 9i , for some events, it is not easy to tell whether they are normal or unusual. Hi Tom, In our very very active database, the top session always depics most of the wait time in log file sync, the other waits are so less as if i belive that the database does actually what?

However this is not enough , we want the database to perform faster , as we anticipate large volumes of load. We have mb of redo logs-6 groups, and log siwtching is around 7 per hr. The application is not commiting every sql, its tran based but since it relates to shares stock ipo etc, the commit rates are always higher, we have 40, concurrent connections, and wil reach 60k offcourse these are from 10gas, db has dedicated mode connections from 3 10gas clusters java cheers.

December 22, - pm UTC. If your big shop made the strategic decision to go all "raid 5", knowing that - well, raid 5 has never been proclaimed "the best thing ever for high throughput writes" I can only tell you what will make log file sync waits become "reduced" o make redo disk faster o do not commit as frequently batch up.

Well I must ask you to please explain why raid5 is heavy on writes, and if not raid 5, then what raid should we use for redo logs and archived logs? Then I can have a debate with my unix admin that even though they have made raid5 for shark, they can always go back and reconfigure the shark to use other raid.

What if i ask them to let me use raw device om shark storage, it would still be raid5 but would that help? And after seeing the stats report, do you really think its worth it changing the redo logs raid device?

It is well known for "not being the best thing for writing to". If your goal is to remove log file sync I'd trace the truly important applications - not with statspack - to confirm THEY are log file sync "bound" , then a reducing the commit frequency b making the log devices faster are your choices.

As for your last question - it is LIKELY that you need to attack this problem, you are not going to be committing anything any faster. A reader, December 22, - pm UTC. Well, I guess am stuck then, if i cant reconfigure raid. About application design, well the aplication is very simple, for every order placed by the client to buy or sell a stock, there are 10 executions 10 sql statements inserts into log table, select from other tables these are 5 select statement , then insert into order table, then after another couple of updates,it commits.

Since the app is very very oltp intensive, our customers are increasing as you know saudi arabia recentl joining wto and lots of companies are now offering ipo and their stocks for public , there is a lot of liquidity and hence the load. We dont mind scalling up the db server with cpu or ram, but if we do not know anything with the throuput of the db, we wil have problems, even nowaways we have had two issues which oracle tar has confirmed we have hit a bug for which they issue us a one off patch and will include that in , this bug was fixed in but oracle did not have this in until now with us, oracle has themslves asked us not to upgrade to as it has several other bugs.

In short the problem we have had was lib cach contention, parses , and cache buffer chains. Anyway sorry to give you the whole story,but the point is we need to do something to out db to increase the throuput and we are open to all ideas. We have noted that when you are into very high oltp app, the database features are really sometomes hit back at you. The point is there is nop perfect world with oracle for high oltp trans. The people buying the disk had to know what raid-5 means.

Yes we are thinking of buying faster disks, there are solid state disks available as well. Our db is almost cached in mem cach hit ratio is perfect. I was wondering if you could point out to me any valid document that states RAID5 is not good at all for oralce databases, the people who bough raid 5 claimed now they bought it for the database as raid 5 offers read efficiency better that any other raid and yes we do not have problm with db, as you see no scattered or seq read.

I am thinking of even having a local disk attached to the machine with raid 10 and placing redo logs there, while the db can still reside on shark.

I Thank you for your input, cheers. I never said raid-5 wasn't good at all for Oracle databases. In fact for some people, it does just fine. According to the statspack info 'log file parallel write' takes an average of 1 ms. The average wait for 'log file sync' is 22 ms. Why bother about getting faster IO? Well actuallt this was suggested by oracle tar engineer that our db is having waits on log file sync and that we should move our redo logs to faster disks.

If you see in the top 5 wait, the waits on log file syncg tops other waits,and this is 15 mins statspack report, which is the first 15 minutes when the trading market opens. However throughtout the remainder of trading time 90 more minutes , more or less the same log file sync tops the waits. I have a redo log buffer of 6MB in size and am not using multiple db writers as aix is doing async io, however as per tom the logwr process is sync and raid 5 is fine for data files, but not for redo makes sense in his example of oltp and datawarehousing.

However I wonder that if raid5 is not good for writing but best for reading, would it not be a tradeoff to put redo on raid10, becuase then prob the archiver process would be slower and comes as top event. Having redos on raid 5 may not be good for logwr but i guess its best for archiver. Our db is not in archive mode by the way and we plan to move it to archive mode to have the dataguard for dr site. I cant batch the commits as its alreay doptimised, you cant batch commits in a synamic application lie ours.

For faster disks, I wish i have some kind of proof or stats that will show that if we move to raid10, log file sync will dropped significantly, i just dont want to go for raid10 or no raid at all, and then see if i get some benfit considering my statspack results.

If any one is interested to know more, write to me at danielmex yahoo. Frequent commits ravinder matte, February 03, - pm UTC. Tom, could you please give me a scenario where frequent commits causes log file sync. Thanks Matte. February 03, - pm UTC. Hi Tom, Thanks for your invaluable service to the oracle community. Apologies for not keeping my text short. We are running on Oracle 9i R2 9. It uses Dynamic SQLs.

Its a transactional system and its max usage is from Jan to May. I have been asked to give a quick fix on this. I dont have a baseline of the performance in the old server as I have joined new to this team. No performance stats history is available. The same performance problem was faced 1yr back ,but the problem was not resolved then. Our disk IO were high and more physical reads.

Now the top 5 events are CPU,log file sync.