Re: Difference in writer response time

Thanks a lot, Tanel.

I got the SAN IO statistics report from the infra team for two of the days where application was pointing and was experiencing issues in DR but not in primary. What i see is the IO rate(i.e. read/sec) in the attached file(primary_DR_SAN_Stats.xlsx) , seems to be on higher side when application was pointing to DR, but in both the cases i don't see any increase in avserv i.e. average service time , so should we conclude that , even we have some additional processes might be running on DR but should not matter as long as the IO service time is almost zero and also no queuing is observed from SAN standpoint for DR? But yes this does not match with the picture which AWR shows i.e. DBWR response time slowness in DR as compared to primary.

Additionally in the AWR which i had shared here earlier in this thread, for DR as it shows "index contention" as the top most wait and there does exist "ITL '' waits(in enqueu_activity_dr.xlsx) , so should we increase the INITRANS value to help us improve the situation here on DR(and also in primary) without any negative impact?

Regards
Pap

On Sun, Apr 11, 2021 at 7:36 AM Tanel Poder <tanel_at_tanelpoder.com> wrote:

> The primary and DR run on different storage arrays that may be configured
> and "sized" differently (sometimes DR/backup has slower disks or something
> like that). Or even if the storage arrays, HBAs & SAN network are identical
> across both environments, the DR storage array may be overloaded more than
> primary (as everyone's doing their backups from DR).
>
> On HP-UX as a starting point, you could use some IO monitoring tool that
> (like sar) that shows you both the I/O rate this server is running & the
> average service time (avserv) and avwait/avque (queue lengths). So, if the
> DR has twice higher I/O service time than primary, while the I/O rate is
> roughly the same (as AWR metrics indicated), then this should be a good
> starting point for sysadmins/storage folks.
>
> $ sar –d 1 10
>
> HP-UX server01 B.11.23 U ia64 10/25/09
>
> 20:38:46 device %busy avque r+w/s blks/s avwait avserv
> 20:38:56 c0t0d0 1.30 0.50 3 50 0.00 11.07
> c31t2d2 0.80 0.50 1 14 0.00 9.22
> c31t2d0 3.30 0.50 5 96 0.00 6.14
> c31t2d1 3.80 0.50 5 85 0.00 7.30
> c31t2d4 1.20 0.50 2 102 0.00 6.04
> c31t2d6 0.10 0.50 0 5 0.00 3.83
> c31t2d3 2.80 0.50 6 96 0.00 4.67
> c31t2d5 1.10 0.50 1 22 0.00 8.44
> c31t2d7 0.40 0.50 1 13 0.00 4.90
> c31t3d1 0.50 0.50 1 11 0.00 7.95
>
> --
> Tanel Poder
> #vConf2021: Troubleshooting Very Complex Oracle Performance Problems
> https://tanelpoder.com/conference/
>
> On Sat, Apr 10, 2021 at 3:54 PM Pap <oracle.developer35_at_gmail.com> wrote:
>
>> As it almost seems like the DR side is performing badly because of some
>> additional process/database might be there which is still running and
>> adding overhead. So what kind of information/stats from the host or
>> SAN should we ask which will help us in identifying the contribution of
>> each of the processes in primary and DR and this would be able to find the
>> exact culprit which is creating a difference during that peak period?
>>
>> Regards
>> Pap
>>
>> On Sat, Apr 10, 2021 at 12:48 AM Pap <oracle.developer35_at_gmail.com>
>> wrote:
>>
>>> Got to know there are other 3 databases on this box, however at exactly
>>> same time we also see a small spike in top activity graph in another
>>> database. And i see even when we were live on Primary that other database
>>> on DR having that small spike exists , which suggests some problem
>>> persisting in the box level rather in the impacted database which we are
>>> looking for. So it may be either at host or storage(which the SAN team is
>>> denying though).
>>>
>>> And another thing is even we saw in the AWR we are doing large amount of
>>> work or the db block changes were on higher side on primary as compared to
>>> DR , but the SAN team saying higher IOPS in DR as compared to primary
>>> during that time observed without any queuing. So it sounds strange. So,
>>> Just like database AWR report, Is there any such historical report which we
>>> can generate out of the HP host or underlying SAN to understand what exact
>>> process/database contributes how much during that peak time? And what is
>>> the exact IO latency trend and segregation based on database , during that
>>> time?
>>>
>>> Regards
>>> Pap
>>>
>>> On Fri, Apr 9, 2021 at 7:54 PM Pap <oracle.developer35_at_gmail.com> wrote:
>>>
>>>> But isn't it correct to say that system stats or dictionary stats can
>>>> only influence the optimizer to go for a different execution path? But in
>>>> our case both of the databases are giving an equal execution path, we don't
>>>> see any difference in execution path for any such sql which can cause this
>>>> issue. It's mainly the single row inserts/updates are running longer on DR
>>>> as compared to primary during peak period.
>>>>
>>>> Regards
>>>> Pap
>>>>
>>>> On Fri, Apr 9, 2021 at 7:50 PM Athil Meer <athildba_at_gmail.com> wrote:
>>>>
>>>>> Hello Pap,
>>>>> Are there any difference in fixed, dictionary and system stats between
>>>>> these DBs
>>>>>
>>>>> Thank you
>>>>> Athil
>>>>>
>>>>> On Fri, 9 Apr 2021, 5:09 pm Pap, <oracle.developer35_at_gmail.com> wrote:
>>>>>
>>>>>> We have both application server and db server based out of primary
>>>>>> and DR side each. So when we point to DR our application code/server also
>>>>>> runs from DR only. So there should not be any network delay causing such
>>>>>> difference.
>>>>>>
>>>>>> Regards
>>>>>> Pap
>>>>>>
>>>>>> On Fri, Apr 9, 2021 at 6:49 PM Mark W. Farnham <mwf_at_rsiz.com> wrote:
>>>>>>
>>>>>>> In a network sense, where is the client application with respect to
>>>>>>> the two databases?
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> When you are using the “primary” database is the client at the
>>>>>>> “primary” database location?
>>>>>>>
>>>>>>> When you are using the “DR” database is the client at the “DR”
>>>>>>> database location?
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> Depending on how the application handshakes information to be
>>>>>>> written and how waits are rolled up, that can make all the difference.
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> A very quick test is to actually place a client at the location of
>>>>>>> the “DR” database location on the LAN with the “DR” database if in fact
>>>>>>> currently you are considering performance of an application on the
>>>>>>> “primary” database location in both cases currently.
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> Explaining how and why the performance difference can actually be
>>>>>>> network latency and speed yet appear to be differences in DBWR service rate
>>>>>>> is beyond the scope of this note.
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> mwf
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> *From:* oracle-l-bounce_at_freelists.org [mailto:
>>>>>>> oracle-l-bounce_at_freelists.org] *On Behalf Of *Pap
>>>>>>> *Sent:* Friday, April 09, 2021 8:29 AM
>>>>>>> *To:* Tanel Poder
>>>>>>> *Cc:* Oracle L
>>>>>>> *Subject:* Re: Difference in writer response time
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> Thank You Tanel.
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> Not having much understanding with respect to the infra side. But ,
>>>>>>> actually the first thing we want to understand is why there is a difference
>>>>>>> in performance during that peak period between the two sites. As those are
>>>>>>> primary and DR so ideally everything should be the same including SAN
>>>>>>> configurations. We have verified all the DB parameters are mostly the same
>>>>>>> and are not suspected such as to impact DBWR throughput one vs other.
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> But as you said there may be some issue wrt kernel or IO stack, so
>>>>>>> wanted to understand what exact information we can ask from our storage/SAN
>>>>>>> team by which we can conclude is there is really a difference in
>>>>>>> performance of storage IO between both sides?
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> And should we ask the IO information only during the issue period to
>>>>>>> understand the difference as because in normal time both the databases
>>>>>>> perform similar just that during those peak activity the DR is behaving
>>>>>>> badly as compared to primary?
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> Regards
>>>>>>>
>>>>>>> Pap
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> On Fri, Apr 9, 2021 at 5:32 AM Tanel Poder <tanel_at_tanelpoder.com>
>>>>>>> wrote:
>>>>>>>
>>>>>>> Ok, sorry I didn't realize this was on HP-UX (I guess I'm too
>>>>>>> spoiled nowadays with "servers" like this one
>>>>>>> <https://tanelpoder.com/posts/11m-iops-with-10-ssds-on-amd-threadripper-pro-workstation/>
>>>>>>> under my desk ;-)
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> Some comments:
>>>>>>>
>>>>>>> 1. The *free buffer waits* show that DBWR falls behind with
>>>>>>> syncing dirty buffers to disk (~4000 blocks written per second). So
>>>>>>> it looks like a DBWR throughput problem (caused by some issue in the kernel
>>>>>>> or I/O stack)
>>>>>>> 2. Other than storage hardware latency itself and things like
>>>>>>> block device queue depths, the filesystem itself may be a bottleneck - are
>>>>>>> you using *VxFS *- and if yes, with or without *ODM*? VxFS
>>>>>>> without ODM doesn't use concurrent I/O by default, potentially causing
>>>>>>> write-write contention at file level (POSIX single writer locking)
>>>>>>> 3. Also, the normal recommendation for production systems is to
>>>>>>> use filesystemio_options=*setall*, but I don't remember if HP-UX
>>>>>>> was special in that sense (or you just forced direct I/O with a VxFS mount
>>>>>>> option)
>>>>>>> 4. Run Snapper on DBWRs and see how many of them you have in
>>>>>>> each instance and are they 100% busy waiting for one of the *db
>>>>>>> file parallel write*, *db file asynch I/O submit* waits (or show
>>>>>>> all CPU usage - no wait events whatsoever, can be due to an instrumentation
>>>>>>> bug)
>>>>>>>
>>>>>>> The various "higher level contention" wait events, *buffer busy
>>>>>>> waits*, *enq: TX contention *and in rare cases even some latch
>>>>>>> contention may be just a symptom of the underlying I/O problems. You need
>>>>>>> to do wait chain analysis to see beyond the "top level symptoms".
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> The ash_wait_chains.sql output is pretty wide, Oracle-L doesn't
>>>>>>> allow me to send screenshots as images, so here are a couple of tweets with
>>>>>>> images of such problems (where the high level symptoms show different waits
>>>>>>> than the root cause):
>>>>>>>
>>>>>>> - https://twitter.com/TanelPoder/status/1318023393304825856
>>>>>>> - https://twitter.com/TanelPoder/status/1380304923678498820
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> Back when I used to deal with HP-UX/Solaris machines with VxFS more,
>>>>>>> a really common bottleneck in high-performance databases (of that era) was
>>>>>>> people not using concurrent I/O on that filesystem.
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> --
>>>>>>>
>>>>>>> Tanel Poder
>>>>>>>
>>>>>>> #vConf2021: Troubleshooting Very Complex Oracle Performance Problems
>>>>>>>
>>>>>>> https://tanelpoder.com/conference/
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> On Thu, Apr 8, 2021 at 2:05 PM Pap <oracle.developer35_at_gmail.com>
>>>>>>> wrote:
>>>>>>>
>>>>>>> Thank you Tanel.
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> Its HP machine and its on file system. No ASM. The
>>>>>>> filesystemsio_options in gv$paramer showing as "asynch" in both databases.
>>>>>>> and also disk_asynch_io is also set as TRUE. As I see from AWR, Its HP-UX
>>>>>>> IA(64 bit), 64 core, 8- socket machine in both side.
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> The SAN team confirms not much visible difference between the
>>>>>>> underlying storage performance between those two sites. So wondering as we
>>>>>>> don't use data guards could this difference be just because of just the
>>>>>>> structural difference in table/index structure? But we have all the same
>>>>>>> volume of data on both sides so not sure how that can play such a big
>>>>>>> difference. And contrary to that, I see we are doing more work on the
>>>>>>> Primary(faster) side during that time period as compared to DR(slow side),
>>>>>>> so how is that possible? I am seeing the direct write is higher on DR i.e.
>>>>>>> slow side as compared to primary, not sure if that is pointing to something
>>>>>>> suspicious.
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> I have fetched the wait event section of the AWR from both databases
>>>>>>> and attaching here(in two tabs as primary and DR wait profile). Although I
>>>>>>> do see "free buffer waits" in one of the top lists but the major one is
>>>>>>> 'index contention'(top one is a composite PK index but local index, so less
>>>>>>> chances of structural difference causing such issues). But again it might
>>>>>>> be that the DBWR response trend is just a symptom of something else but not
>>>>>>> the cause as the SAN team is saying no difference there.
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> Regards
>>>>>>>
>>>>>>> Pap
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> On Thu, Apr 8, 2021 at 10:34 PM Tanel Poder <tanel_at_tanelpoder.com>
>>>>>>> wrote:
>>>>>>>
>>>>>>> There's also one usual suspect, I don't see *filesystemio_options*
>>>>>>> parameter set, are you running on ASM, not a filesystem, right?
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> Thanks,
>>>>>>>
>>>>>>> Tanel.
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> On Thu, Apr 8, 2021 at 4:06 AM Pap <oracle.developer35_at_gmail.com>
>>>>>>> wrote:
>>>>>>>
>>>>>>> Hello Lister, We have two databases which are the same in all the
>>>>>>> hardware configurations along with DB parameters and are in sync/replicated
>>>>>>> using golden gate. And those are treated as primary and DR for us and both
>>>>>>> are active. But we are seeing differences in behaviour when our application
>>>>>>> points to primary VS when it points to DR. We are seeing during specific
>>>>>>> times of the day when our system is at its peak, in one of the database i.e
>>>>>>> DR the DBWR response times spikes till ~200+ms slowing down the write
>>>>>>> queries while in another database the dbwr response time stays ~65ms for a
>>>>>>> similar amount of data and transaction volume. So wanted to understand what
>>>>>>> can cause such drastic differences? Note- Its version 11.2.0.4 of Oracle.
>>>>>>>
>>>>>>>

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application/vnd.openxmlformats-officedocument.spreadsheetml.sheet attachment: Primary_DR_SAN_Stats.xlsx



application/vnd.openxmlformats-officedocument.spreadsheetml.sheet attachment: Enqueue_activity_DR.xlsx