Re: LGWR, EMC or app cursors?

From: Mladen Gogala <gogala.mladen@xxxxxxxxx>
To: oracle-l@xxxxxxxxxxxxx
Date: Mon, 7 Oct 2019 18:56:15 -0400

On 10/7/19 11:17 AM, Herring, David (Redacted sender HerringD for DMARC) wrote:

I am stuck trying to find out, really prove who is the culprit or what exactly the wait is on. Is LGWR waiting on user sessions and user sessions are waiting on LGWR and all that causes the disk to be 100%? Can I enable some sort of tracing on LGWR and would that point to exactly what he's waiting on to prove where the problem is?

Regards,

Dave

Hi Dave!

Is there anything in /var/log/messages? Can you check disks using smartctl? That should look something like this:

root@umajor:~# smartctl -a /dev/sda
smartctl 6.6 2017-11-05 r4594 [x86_64-linux-5.0.0-32-generic] (local build)
Copyright (C) 2002-17, Bruce Allen, Christian Franke, www.smartmontools.org

=== START OF INFORMATION SECTION ===
Device Model:     Samsung SSD 860 QVO 2TB
Serial Number:    S4PHNF0M200370J
LU WWN Device Id: 5 002538 e40d20892
Firmware Version: RVQ01B6Q
User Capacity:    2,000,398,934,016 bytes [2.00 TB]
Sector Size:      512 bytes logical/physical
Rotation Rate:    Solid State Device
Form Factor:      2.5 inches
Device is:        Not in smartctl database [for details use: -P showall]
ATA Version is:   ACS-4 T13/BSR INCITS 529 revision 5
SATA Version is:  SATA 3.2, 6.0 Gb/s (current: 6.0 Gb/s)
Local Time is:    Mon Oct  7 18:52:18 2019 EDT
SMART support is: Available - device has SMART capability.
SMART support is: Enabled

=== START OF READ SMART DATA SECTION ===
SMART overall-health self-assessment test result: PASSED

General SMART Values:
Offline data collection status:  (0x00)    Offline data collection activity
                    was never started.
                    Auto Offline Data Collection: Disabled.
Self-test execution status:      (   0)    The previous self-test routine completed
                    without error or no self-test has ever
                    been run.
Total time to complete Offline
data collection:         (    0) seconds.
Offline data collection
capabilities:              (0x53) SMART execute Offline immediate.
                    Auto Offline data collection on/off support.
                    Suspend Offline collection upon new
                    command.
                    No Offline surface scan supported.
                    Self-test supported.
                    No Conveyance Self-test supported.
                    Selective Self-test supported.
SMART capabilities:            (0x0003)    Saves SMART data before entering
                    power-saving mode.
                    Supports SMART auto save timer.
Error logging capability:        (0x01)    Error logging supported.
                    General Purpose Logging supported.
Short self-test routine
recommended polling time:      (   2) minutes.
Extended self-test routine
recommended polling time:      ( 160) minutes.
SCT capabilities:            (0x003d)    SCT Status supported.
                    SCT Error Recovery Control supported.
                    SCT Feature Control supported.
                    SCT Data Table supported.

SMART Attributes Data Structure revision number: 1
Vendor Specific SMART Attributes with Thresholds:
ID# ATTRIBUTE_NAME          FLAG     VALUE WORST THRESH TYPE      UPDATED WHEN_FAILED RAW_VALUE
5 Reallocated_Sector_Ct   0x0033   100   100   010 Pre-fail Always       -       0
9 Power_On_Hours          0x0032   099   099   000 Old_age   Always       -       2110
12 Power_Cycle_Count       0x0032   099   099   000 Old_age   Always       -       550
177 Wear_Leveling_Count     0x0013   099   099   000 Pre-fail Always       -       2
179 Used_Rsvd_Blk_Cnt_Tot   0x0013   100   100   010 Pre-fail Always       -       0
181 Program_Fail_Cnt_Total 0x0032   100   100   010 Old_age   Always       -       0
182 Erase_Fail_Count_Total  0x0032   100   100   010 Old_age   Always

See if you can decipher anything from the smartctl output.

--
Mladen Gogala
Database Consultant
Tel: (347) 321-1217

References:
- LGWR, EMC or app cursors?
  - From: Herring, David

Re: LGWR, EMC or app cursors?

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