Tag: hidden parameters

Database, Errors and Bugs, Migration | Upgrades | Patching, Performance

Advise: Setting underScore/Hidden Parameters

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Please be aware no hidden parameters (parameters starting with “_”) should not be set unless recommended by Oracle explicitly or in case of a perfect match to the case.

This is explained on MOS Best Practices and Guidelines for Setting underScore/Hidden Parameter to Workaround and/or Resolve Customers Problems (Doc ID 2524119.1)

So, in case of any diagnostics you have to lead to setting it, SUGGESTED:

  • Get the explicit approval/agreement from Oracle.
  • Include evidence on the root cause for this setting. A comment should work, something like:
alter system set "_replace_virtual_columns"=false Comment= 'Workaround Doc ID 1512347.1' SID= '*' scope= both;

Cheers!

Database, SQL | PLSQL

Getting Oracle Parameters: Hidden and Unhidden

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Today’s post is a quick post!
Very quick post! very very quick post!
But it’s a helpful post!

Connected as sys with sysdba:

select x.ksppinm name,
ksppdesc description,
y.kspftctxvl value,
y.kspftctxdf isdefault,
decode(bitand(y.kspftctxvf, 7), 1,'MODIFIED',4,'SYSTEM_MOD','FALSE') ismod, decode(bitand(y.kspftctxvf, 2), 2, 'TRUE', 'FALSE') isadj
from sys.x$ksppi x, sys.x$ksppcv2 y
where x.inst_id = userenv('Instance')
and y.inst_id = userenv('Instance')
and x.indx + 1 = y.kspftctxpn
order by name;

Matheus.

Database, Performance, RAC | Data Guard

High CPU usage by LMS and Node Evictions: Solved by Setting “_high_priority_processes”

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Another thing that may help you in environments with highly interdependent applications:

Our env has high interconnect network block changing, and, as a consequence, high CPU usage by Global Cache Services (GCS)/Lock Manager Server Process (LMS).

This way, for each little latency in the interconnect interface, we were having a node eviction and all the impacts to the legacy application you can imagine (without gridlink or any solution to make the relocation ‘transparent’, as is usual to legacy application) and, of course, the business impact.

Oracle obviously suggested that we reduce the block concurrency over the cluster nodes grouping the application by affinity. But, it’s just no applicable to our env… 🙁

When nothing seemed to help, the workaround came from here: Top 5 Database and/or Instance Performance Issues in RAC Environment (Doc ID 1373500.1).

Here is our change:

boesing@proddb> alter system set "_high_priority_processes"='LMS*|LGWR|VKTM' scope=spfile sid='*';
System altered.

No magic, but the problem stopped to happen. After that, we’re having some warnings about clock synchronization over the cluster nodes on CRS alerts. Like this:

CRS-2409:The clock on host proddb1 is not synchronous with the mean cluster time. No action has been taken as the Cluster Time Synchronization. Service is running in observer mode.

I believe it happens because VKTM lost priority. But it’s OK: The node evictions has stopped! 😀

Matheus.