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November 2013

When do Oracle Parallel Execution Slaves issue buffered physical reads – Part 1?

This post applies both to non-Exadata and Exadata systems.

When do Oracle Parallel Execution Slaves issue buffered physical reads – Part 1?

This post applies both to non-Exadata and Exadata systems.

Before Oracle 11.2 came out, it was true to say that Oracle Parallel Execution slaves always do direct path reads (bypassing buffer cache) when doing full segment scans. This should not be taken simplistically though. Even when you were doing full table scans, then yes the scanning was done with direct path multiblock reads – but if you had to visit other, additional blocks out of the scanning sequence, then these extra IOs were done with regular buffered reads. For example, next row piece fetching of chained rows or or undo block access for CR reads was done with buffered single block reads, or even buffered multiblock reads, if some form of prefetching kicked in.

Inside a RAC 12c GNS cluster

Based on some reader feedback I started looking at GNS again, but this time it will be for RAC 12c. According to the documentation GNS has been enhanced so that you can use it without subdomain delegation. I decided to try the “old fashioned” way though: DHCP for VIPs, SCAN IPs, subdomain delegation and the like as it is the most complex setup. I occasionally like complex.

The network setup is exactly the same as I used before in 11.2 and thankfully didn’t require any changes. The cluster I am building is a 2 node system on Oracle Linux 6.4 and the Red Hat compatible kernel. I have to use this as the Unbreakable Kernel doesn’t know about block devices made available to it via virtio-scsi. I use virtio-scsi for shared block devices very much in the same way I did for Xen.

Result Cache Latch and PDBs

One interesting aspect of Oracle 12cR1 database when it comes to PDBs is how latching is done. For example, if all PDBs have to work under the same latch then contention in one PDB can easily affect users in other PDBs too.

Continuing my series of posts on the Result Cache latch today I'll check what happens when you try to acquire RC latch from two different PDBs.

Session 1

The first session is connected under container name TEST:





SQL> select sys_context('userenv', 'con_name') con_name from dual;

CON_NAME
--------------------
TEST

SQL> select addr from v$latch where name='Result Cache: RC Latch';

ADDR
----------------
0000000060041C78

Session 2

The second session is connected under container name TEST2:

SQL> select sys_context('userenv', 'con_name') con_name from dual;

CON_NAME
--------------------
TEST2

OakTable World UK 2013

OakTable World UK 2013 Conference - Manchester 2-3 December 2013
Event date: 
Mon, 2013-12-02 - Tue, 2013-12-03

Drill Down the I/O stack at UKOUG Tech13

It’s just under a week to go before the doors open for the UKOUG Tech13 conference and the adjoining OakTable World UK 2013 sessions, so I thought I would write a very short blog post about what I will be doing there, where I’ll be, and what I’m looking forward to. This year I will … Continue reading "Drill Down the I/O stack at UKOUG Tech13"

Drill Down the I/O stack at UKOUG Tech13

It’s just under a week to go before the doors open for the UKOUG Tech13 conference and the adjoining OakTable World UK 2013 sessions, so I thought I would write a very short blog post about what I will be doing there, where I’ll be, and what I’m looking forward to. This year I will … Continue reading "Drill Down the I/O stack at UKOUG Tech13"

Drill Down the I/O stack at UKOUG Tech13

It’s just under a week to go before the doors open for the UKOUG Tech13 conference and the adjoining OakTable World UK 2013 sessions, so I thought I would write a very short blog post about what I will be doing there, where I’ll be, and what I’m looking forward to. This year I will … Continue reading "Drill Down the I/O stack at UKOUG Tech13"

OTNYathra 2014 : India OTN Tour

Just a quick note to say the top-level approval for OTNYathra 2014 – India OTN Tour has been granted. Next, we’ve got to submit our individual travel approvals and see how that goes. If everything goes to plan, I will be representing the Oracle ACE Program on this tour in February, which visits the following locations.

  • Jallandar – 18th February
  • Delhi - 20th February
  • Mumbai - 22nd February
  • Pune - 23rd February
  • Hyderabad - 25th February
  • Bangalore - 27th February
  • Chennai – 1st March

Fingers crossed everything goes to plan. :)

Cheers

Tim…

12c Adaptive Optimization – Part 1

Last week I did a webinar on 12c Adaptive Optimization. The talk was recorded. The slides are here: 12c Adaptive Optimization V2 PDF. The recording can be found here: 12c Adaptive Optimization Recording. There were a number of follow up questions and emails so I thought I’d summarize here. Since there were so many questions, (I guess I must not have done that good of a job of explaining how it works) I will break them up into 2 or 3 posts. So for this first one I will just cut and paste from a couple of email follow ups.

Here’s the first question(s):

Hi Kerry,