Oracle In Memory Column Store

I attended the Greater Cincinnati Oracle User’s Group meeting yesterday at the local Oracle office. I was expecting a good presentation because Maria Colgan (@sqlmaria) was presenting.

I was not disappointed and this was an excellent presentation and conversation with Maria who used to head up the optimizer team and now runs the In Memory team.  She went into deep dives of a lot of technical innovations they have used for performance and reliability. I took lots of notes.

All of the code is embedded in Oracle database software (12.1) so it’s just a parameter change to turn it on. The only other step is to alter table INMEMORY. Some of the inmemory stuff can be offloaded to Exadata but you have to pay the license when you turn it on.

In Oracle 12.2 the whole thing can run in exadata flash instead of in the db server dram. Oracle 12.2 will be out “sometime this year”.

SQLDeveloper on Oracle Enterprise Linux 6.3

Today while installing SQLDeveloper on OEL 6.3 I ran into a couple of issues I wasn’t expecting. The installation went fine using the Oracle rpm file. The first execution of the /opt/sqldeveloper/sqldeveloper.sh script prompted for the location of a jdk. A find came up with /etc/alternatives/java_sdk_openjdk and that worked fine. The next issue was “Can’t connect to X11 window server using ‘:0.0’ as the value of the DISPLAY variable”. I tried running xterm to see if it would work. Xterm was not installed on the system and I couldn’t find any of the other X11 stuff. So I ran “yum install xterm”. Now xterm works and so does SQLDeveloper.

RAC on AIX

I just finished the class: X0161 Oracle RAC on AIX Systems Workshop taught by Andrei Socoliuc of IBM Romania. Andrei knew a lot about Oracle RAC and AIX so it was a good class. I thought the best part was the hands on labs, especially the pre-installation preparation of the operating system. There was also a lot of good information on hardware and LPAR configuration. This is my first RAC class since 2003 when it had just been released, so the overview of RAC was a good way for me to get a refresher on RAC internals. My only complaint  is that we spent a lot of time on IBM’s shared disk solution (GPFS) and very little on Oracle’s ASM .

How do I know if the cardinality estimates in a plan are accurate?

Maria Colgan has another great blog post today about using the GATHER_PLAN_STATISTICS hint to see the actual rows returned as well as the optimizer’s estimate of number of rows returned.  This is very good information and will make it obvious if your statistics are wrong.

CRS-2800: Cannot start resource ‘ora.asm’ as it is already in the INTERMEDIATE state on server

I got this error when I was installing Oracle RAC 11.2 on Red Hat Enterprise Linux 5.6.  I was installing Clusterware using ASM on VMware shared disks.  When I created the independent persistent virtual disks, I left the “allocate all disk space now” option unselected. Oracleasm was happy on both RAC nodes. The Oracle installer was happy when it created +ASM1 on the first RAC node. But when the ASM instance started on node 2 it did not like the “virtually provisioned” disk. The +ASM2 instance was not open and was complaining about one of the shared disks being corrupt at a certain byte. When I checked the virtual disk files, I saw that Oracle was trying to read past the end of the file. I started all over with new fully allocated shared disk and that fixed the problem. Everything is up and running now.