ORA-00600, ORA-07445 and ORA-00020 errors and related bugs in 12c (12.2.0.1)

I have come across below error recently in 12c (12.2.0.1). It first started with ORA-00600 followed by ORA-07445 and ORA-00020. The ORA-00600, ORA-07445 looks like real culprit and which lead to ORA-00020 error.

ORA-00600: internal error code, arguments: [17126], [0x0B0D29528], [], [], [], [], [], [], [], [], [], []
Use ADRCI or Support Workbench to package the incident.
See Note 411.1 at My Oracle Support for error and packaging details.
2020-01-13T23:20:30.493308-08:00
Exception [type: SIGSEGV, Address not mapped to object] [ADDR:0x32000000170] [PC:0x10F9D3FD, kghfnd_in_free_lists()+717] [flags: 0x0, count: 1]
Errors in file /home/oracle/diag/rdbms/ORADB/ORADB/trace/ORADB_ora_62437.trc (incident=41538):
ORA-07445: exception encountered: core dump [kghfnd_in_free_lists()+717] [SIGSEGV] [ADDR:0x32000000170] [PC:0x10F9D3FD] [Address not mapped to object] []
Incident details in: /home/oracle/diag/rdbms/ORADB/ORADB/incident/incdir_41538/ORADB_ora_62437_i41538.trc
Use ADRCI or Support Workbench to package the incident.
See Note 411.1 at My Oracle Support for error and packaging details.
2020-01-13T23:20:31.182120-08:00
Use ADRCI or Support Workbench to package the incident.
See Note 411.1 at My Oracle Support for error and packaging details.
2020-01-13T23:20:31.182223-08:00
opidcl aborting process unknown ospid (48392) as a result of ORA-600
……

2020-01-14T01:29:37.222083-08:00
ORA-00020: maximum number of processes (500) exceeded
ORA-20 errors will not be written to the alert log for
the next minute. Please look at trace files to see all
the ORA-20 errors.
After investigation and troubleshooting I found below bugs

1. There is a unpublished bug related to Unified memory KGH related crashes/errors. After discussing with support come to know that particular fix was found on an internal note to already be included in Oracle 12.2.0.1

Bug 30053838 - LNX-20-ATP: HIT ORA-7445 [KGHFND_IN_FREE_LISTS] AND ORA-600 [KSM_PGA_UM_EXT_FREE:INVALID_EXT_MAGIC], INST CRASH

2. There is a published bug 24596874 and the fix fix for 24596874 is first included in 20.1.0 . Also in term patches may be available for earlier versions.

For bug 24596874 , users notice Memory corruption when CDB environment is setup with star schema on one PDB. Redaction policies enabled on tables/view of the schema and query workload executed with 50 concurrent sessions. Multiple ORA 600 [kghfrh:ds] were seen in the alert log.

So both of the above bugs are ruled out as unpublished bug already part of 12.2.0.1 and published bug is related to Star schema on PDB.

After further investigation with Oracle support found another unpublished Bug 30448845 : DATABASE HANG WITH SIGNATURE: 'PMON TIMER'<='PRIOR SPAWNER CLEAN UP'<='LATCH FREE'<='RELIABLE MESSAGE'

As per Oracle support, this is fixed in 18.1 but the fix is not easy to backports. Oracle suggest to update parameter _pmon_slaves_arr_size=0 as workaround in Oracle 12.2

Users cannot update internal oracle parameters directly in SPFILE, please follow the steps mentioned in the below blog post
https://www.oracleracexpert.com/2020/01/ora-00800-soft-external-error-arguments.html

Note that every environment, errors, load, use cases are different, I would highly recommend users to open a ticket with Oracle support and get confirmation before making any changes to your databases.
Regards
Satishbabu Gunukula, Oracle ACE
http://oracleracexpert.com