Wednesday Dec 02, 2015

What or who is JOX? And what happens if ...

Are you worried because of the title of this blog post? Don't worry ... it will be about the Oracle database and not about miraculous additives.

Months back I wrote about how to remove options from the Oracle database's kernel by either using chopt or linking options off:

Recently a very interesting case was logged in relation to a bug:
A customer had linked off the JOX option from the database kernel.
.

What is JOX? 

Well, do a quick search for "JOX" in the Oracle Documentation and you'll get "zero results" (or you may get results in the 8.1 and 9.0 documentation which does not help here). So our documentation doesn't want to tell you further details on "JOX". But once you know that this is the acronym for the JavaVM JIT Compiler then we'll get more results leading directly to this spfile parameter:

The default in my environments is always TRUE. It enables or disables the Just-in-Time (JIT) compiler for the Oracle Java Virtual Machine (OracleJVM) environment.

And from here a link guides us into the Java Documentation explaining a bit more details about the JIT in case you are interested. 
.

Why am I writing this?

In theory you can unlink the JOX option - and compile oracle without the JIT:

$ cd $ORACLE_HOME/rdbms/lib
$ /usr/bin/
make -f /u01/app/oracle/product/12.1.0.2/rdbms/lib/ins_rdbms.mk jox_off ioracle

But let me add two things

  • We recently had a bug just happening because JOX was unlinked - all our tests have JOX linked in
  • As you can control the availability of JOX via the above initialization parameter I don't see a deeper reason to unlink JOX
  • And based on the feedback of Marcelo Ochoa (thanks Marcelo!!!) you'll encounter a performance dip in some components such as interMedia, XMLDB etc as code will now be interpreted, and not JIT compiled.
  • Furthermore based on the feedback of my former colleague, Norbert Debes, unlinking JOX may cause also trouble with the upgrade to Oracle Database 12c
My conclusion: There's no real reason to take JOX out of the RDBMS kernel. Please leave it linked in.


How do you find out if JOX is linked in?

You can't query the database for JOX as it is not mentioned in V$OPTION or DBA_REGISTRY. But you can find it out easily on the OS level: 

$ cd $ORACLE_HOME/rdbms/lib
$ ar -t libknlopt.a | grep -c jox.o

If the result is "1" it means "JOX installed", and "0"  means it is not installed.

Credits to Byron Motta from our Database Upgrade team! 

Further information about JIT?

--Mike

Friday Jul 24, 2015

Why does a PDB require an upgrade?

Why do I need to upgrade (or downgrade) a Pluggable Database (PDB) once I unplug it from version A and replug into version B?

This question is one of the most often asked questions in our workshops when Roy and I present Upgrades and Oracle Multitenant.

If you take a look into the documentation you'll find:

But unfortunately this is not 100% correct for every object.

When you do a simple query for basic dictionary structures such as OBJ$ you'll easily find out that a PDB has its own Data Dictionary.  Some things are really linked into the PDB only - check the SHARING column of DBA_OBJECTS for instance. If it says "METADATA LINK" it will give you an indication that it exchanges information with its parent in the CDB$ROOT. But that doesn't mean necessarily that it's just an empty meta object. Some tables do exist in the PDB as well and allocate space. Check it by yourself and you'll find out that OBJ$ inside a PDB has in fact the same attribute - but still owns segments in the PDB and in the CDB$ROOT - as other objects do allocate space as well. And of course the object's definition exists in the PDB as well. 

  • CDB$ROOT

    OBJ$ in CDB$ROOT

  • PDB 

    OBJ$ in PDB
    .

So the answer is simple:
A Pluggable Database (PDB) must be upgraded (or downgraded) when it get moved between versions simply because it has its own data dictionary. And this doesn't get upgraded automatically.
,

 

--Mike 

Friday Nov 29, 2013

Starting up 252 PDBs in Oracle Multitenant

What happens when you start up 252 PDBs (Pluggable Databases) with the Oracle Multitenant Option for the first time?

Interesting question, isn't it? The expectation would be that this will happen within seconds as the SGA and therefore the shared memory segments are already allocated from within the CDB$ROOT (Container Database). But ...

The following happens:
It takes minutes ... hours .... In my tiny lab environment with just as little as 20 PDBs due to space constraints it takes over 30 minutes to startup 21 PDBs. Takashi Ikeda from Fujitsu Hokoriku Systems who did a great demo with the new Fujitsu M10 servers at OOW this year told me that it took over two hours to start up 252 PDBs for the first time.
Why is that?

Let's have a closer look into the alert.log during startup. After issueing the command:

ALTER PLUGGABLE DATABASE ALL OPEN;

I'd expect all PDBs to get started. With an EXCEPT PDB1, PDB2, PDB3 clause I could exclude some PDBs from this action. Now a look into the alert.log shows a very promising message:

I'm just wondering about the opening sequence of PDBs. I'd expect 1 ... 2 ... 3 ... 4 ... ... ... 21. But the "order" is 3 ... 10 ... 16 ... 15 ... 20 ... 21 etc. telling me that the Resource Manager is not active (which is a must if you take Multitenant serious).
OK, for that strange order there's an explanation:
The open action gets distrubuted to slaves so PDBs may opened in a random order.
Fuuny thing apart from that: I can access the PDB but the system seems to be really under heavy pressure. CPUs are all at 100%. What the heck is going on here in the background?

Well, XDB needs to be installed (at least that is what the message says). Strange, isn't it, as the PDB$SEED has XDB in it and all my PDBs got provisioned from it. The awkward thing here is that the XDB messages appear over 20 minutes AFTER the PDBs signaled the Opening message into the alert.log (see the time stamps above).

Now after exchanging a few emails with some very helpful people in development there's an explanation for the XDB messages as well. Actually it doesn't get really installed but the SGA needs to be initialized for XDB. And I'm guessing that this action takes a lot of resources plus may cause contention when many PDBs get opened at the same time. And there's optimization work going on right now meaning that a problem with port initialization within the PDB will get fixed in a future patch set. So this issue with the very long startups of PDBs because of XDB should disappear in 12.1.0.2 most likely :-)

Finally it took another while to get the PDBs really into OPEN mode. Even though they were showing OPEN before already in V$PDBS. But as the CPUs all went to 100% as XDB got installed/initiallized at more or less the same time in all PDBs you really can't do anything.

Finally ...

... all PDBs got opened and the command ALTER PLUGGABLE DATABASE ALL OPEN returned completed.

The good news:
It takes just this long during the initial startup of a newly provisioned PDB. And you may see this issue only when you try to open many PDBs at the same time. But have a close look into your alert.log if you'll spot the message after creating a fresh PDB.

And btw, just for the records: I was using Oracle Database 12.1.0.1 with Oct 2013 PSU in it.

-Mike

About

Mike Dietrich - Oracle Mike Dietrich
Master Product Manager - Database Upgrade & Migrations - Oracle

Based in Germany. Interlink between customers/partners and the Upgrade Development. Running workshops between Arctic and Antartica. Assisting customers in their reference projects onsite and remotely. Connect via:

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