"SELECT SPARE6 FROM USER$ WHERE USER#=:1" Causes Blocking Sessions, Hangs on RAC on 12.2.x with Infiniband 'gc cr request'<='gc buffer busy acquire'<='library cache lock' Waits on a Single Session (Doc ID 2546022.1)

Last updated on APRIL 17, 2023

Applies to:

Symptoms

Description and context.

After an upgrading, installing or a new RAC configuration on 12.2.x GI and/or database you encounter hangs and notable waits on previous working functionality.

• Application or query Hangs
• Potential high CPU during these Hangs
• DSNMP processes
• Cloud Control / Enterprise Manager / SQL Monitor or AWR reports will show key Waits for

Waits can also be identified using Hang Manager analysis or System State Dumps.

- 'gc cr request'<='gc buffer busy acquire'<='library cache lock'

Further investigation will show that the following query is related.
This query will show a Single Session hanging other sessions.

- "SELECT SPARE6 FROM USER$ WHERE USER#=:1"

Factors associated with the problem are:

• Cluster Configuration (RAC: two or more instances)
• 12.2.x RDBMS 
  on
• 12.2.x GI and
• UEK4 OS
• Enterprise Manager / Cloud Control

Infiniband also appears to be related.
Exadata and ODA are a few of the potential configurations likely to see this problem.

Changes

 Changes associated with this issue

• RAC
• Two or more nodes using Infiniband
• on 12.2.x (GI / Database) 

A possible additional change which might introduce the problem is: 

• Cloud Control or Enterprise Manager 

Note: This problem is frequently only seen after an upgrade to 12.2.x all other things being equal.

Cause

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