Hi Kuba
No, we dont have undocumented parameter set in the Databases.
Thanks
On Fri, Feb 15, 2019 at 1:29 PM Kuba Szepietowski <
kuba.szepietowski@xxxxxxxxx> wrote:
Hi,
"I also obseve something strange, a 128 KB table with 50 rows is being
Smart Scanned in the cells when the buffer cache is 25GB. This also
increase checkpoint activity as well."
Is there any undocumented parameter set on instance level like
_serial_direct_read? more on that here:
https://blog.tanelpoder.com/2013/05/29/forcing-smart-scans-on-exadata-is-_serial_direct_read-parameter-safe-to-use-in-production/
best regards
Jakub
On Thu, Feb 14, 2019 at 8:53 PM Andy Wattenhofer <watt0012@xxxxxxx> wrote:
Maybe it's worth looking further into that controlfile parallel write
wait event. Run an AWR report for a time range where the problem exhibits,
and look for "IOStat by File Type." You can see control file reads and
writes there. If the writes are significantly high, you could cut that
number in half by simply dropping to a single control file. I know that
sounds like a blasphemous thing to do, but it's actually Oracle's best
practice recommendation for your configuration to run just one control file
on the +DATA disk group (reference MOS doc id 2062068.1
<https://support.oracle.com/epmos/faces/DocContentDisplay?id=2062068.1>).
With heavy DML periods you've probably got a lot of redo I/O on the +FRA
disk group already. Maybe as an experiment you can temporarily drop the
+FRA control file and see if it alleviates the wait problem.
Andy
On Tue, Feb 12, 2019 at 5:16 PM Ls Cheng <exriscer@xxxxxxxxx> wrote:
Hi
Running Exadata 18.1.5.0.0. Grid 12.2.0.1, RDBMS 11.2.0.4 and 12.2.0.1.
IORM is default, no custom configuration. Contrlfile set to DATA and FRA
Disk Group and finally ASM High Redundanc
Thanks
On Tue, Feb 12, 2019 at 11:21 PM Andy Wattenhofer <watt0012@xxxxxxx>
wrote:
Which Exadata software version are you running? Which grid and database
versions? Are you using IORM? What is your control_files parameter set to
(i.e., where are your control files)? And what are your ASM redundancy
levels for each of the disk groups?
On Tue, Feb 12, 2019 at 3:16 PM Ls Cheng <exriscer@xxxxxxxxx> wrote:
Hi
IHAC who has 1/8 Exadata x6-2 with High Capacity Disks is having heavy
performance problems whenever some massive DML operation kicks in, since
this is a 1/8 configuration the IOPS supporting write operation is not
high, roughly 1200 IOPS. I am seeing as high as 4000 Physical Writes Per
Sec in peak time. When this happens the user session starts suffering
because they are blocked by enq: KO - fast object checkpoint which is
blocked by "control file parallel write" by CKPT. So the idea is aliviate
CKPT. This is from hist ash
INSTANCE_NUMBER SAMPLE_TIME EVENT
TIME_WAITED SESSION P1 P2 P3
--------------- --------------------------------
------------------------------ ----------- ------- ---------- ----------
----------
2 12-FEB-19 12.11.24.540 AM control file parallel
write 1110465 WAITING 2 41 2
2 12-FEB-19 12.16.34.754 AM Disk file Mirror
Read 1279827 WAITING 0 1 1
1 12-FEB-19 12.16.44.012 AM control file parallel
write 1820977 WAITING 2 39 2
2 12-FEB-19 12.20.34.927 AM control file parallel
write 1031042 WAITING 2 856 2
1 12-FEB-19 12.21.14.256 AM control file parallel
write 1905266 WAITING 2 3 2
2 12-FEB-19 12.21.14.977 AM control file parallel
write 1175924 WAITING 2 42 2
1 12-FEB-19 12.21.54.301 AM control file parallel
write 2164743 WAITING 2 855 2
2 12-FEB-19 12.22.35.036 AM control file parallel
write 1581684 WAITING 2 4 2
1 12-FEB-19 12.23.44.381 AM control file parallel
write 1117994 WAITING 2 3 2
1 12-FEB-19 12.23.54.404 AM control file parallel
write 4718841 WAITING 2 3 2
Whe this happens we observe these cell metrics
CELL METRICS SUMMARY
Cell Total Flash Cache: IOPS=13712.233 Space
allocated=6083152MB
== Flash Device ==
Cell Total Utilization: Small=27.8% Large=14.2%
Cell Total Throughput: MBPS=471.205
Cell Total Small I/Os: IOPS=9960
Cell Total Large I/Os: IOPS=6005
== Hard Disk ==
Cell Total Utilization: Small=69.5% Large=18.7%
Cell Total Throughput: MBPS=161.05
Cell Total Small I/Os: IOPS=5413.618
Cell Total Large I/Os: IOPS=166.2
Cell Avg small read latency: 245.67 ms
Cell Avg small write latency: 62.64 ms
Cell Avg large read latency: 308.99 ms
Cell Avg large write latency: 24.65 ms
We cannot not enable write-back flash cache right now because that may
cause another problems and although we are in process to upgrade 1/8 cells
to 1/4 cells it is going to take some months. I know it is not a best
practice but I was thinking in the mean time scarve some flash space and
create them as grid disk and store the controlfiles in Flash. Anyone have
experience with such setup?
TIA
--
Mit freundlichen Grüße/Best Regards/Pozdrawiam
Jakub Szepietowski
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