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January 2018

Secret Hacking Session: Oracle Background Process Communication, Exotic Wait Events and Some Tracing too

Update: I unexpectedly ended up falling ill and decided to reschedule this hacking session to January 24, 10am PST. No need to re-register if you already have done so. Sorry for the inconvenience. I will upload the video to Youtube after the event.
Since I’m running my Advanced Oracle Troubleshooting Training in the end of this month, I’ll do one of my “secret” hacking sessions too for promotion and noise-making reasons next week!

ASSM tangle

Here’s a follow-on from Tuesday’s (serious) note about a bug in 12.1.0.2 that introduces random slowdown on large-scale inserts. This threat in this note, while truthful and potentially a nuisance, is much less likely to become visible because it depends on you doing something that you probably shouldn’t be doing.

There have always been problems with ASSM and large-scale deletes – when should Oracle mark a block as having free space on deletion: if your session does it immediately then other sessions will start trying to use the free space that isn’t really there until you commit; if your session doesn’t do it immediately when can it happen, since you won’t want it done on commit – but that means the segment could “lose” a lot of free space if something doesn’t come along in a timely fashion and tidy up.

Enterprise Manager and Firewalls

Just a short post, since this is a fairly common question I see. This morning someone asked me a question about Enterprise Manager and firewalls. They have an environment with EM targets placed in different zones / networks – with firewalls between. In the documentation, it states “Each Management Agent is configured to upload data to one OMS. As a result, if there is a firewall between the Management Agent and its OMS, you must configure the firewall to allow the Management Agent to upload data to the OMS using the upload URL.”

and then further

The Future of the DBA, #C18LV, Video 1

I’m starting to move towards doing more videos and hope to improve my video skills, (and maybe add a dance sequence, ya know, like the hip kids…)  Check out this post and please, do add comments, ask questions or just tell me what you think?

Have an awesome Wednesday and no, don’t comment on my consistent need to make a strange face at the beginning of a video… </p />
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ASSM Argh 2

After yesterday’s post one of the obvious follow-up questions was whether the problem I demonstrated was a side effect of my use of PL/SQL arrays and loops to load data. What would happen with a pure “insert select” statement.  It’s easy enough to check:

Spectre and Meltdown, Oracle Database, AWS, SLOB

Last year, I measured the CPU performance for an Oracle Database on several types of AWS instances. Just by curiosity, I’ve run the same test (SLOB cached reads) now that Amazon has applied all Spectre and Meltdown mitigation patches.

I must admit that I wanted to test this on the Oracle Cloud first. I’ve updated a IaaS instance to the latest kernel but the Oracle Unbreakable Enterprise Kernel does not include the Meltdown fix yet, and booting on the Red Hat Compatible Kernel quickly goes to a kernel panic not finding the root LVM.

ASSM argh!

Here’s a problem with ASSM that used to exist in older versions of Oracle had disappeared by 11.2.0.4 and then re-appeared in 12.1.0.2 – disappearing again by 12.2.0.1. It showed up on MoS a few days ago under the heading: “Insert is running long with more waits on db file sequential read”.

How to cancel SQL statements and disconnect sessions in #PostgreSQL

https://uhesse.files.wordpress.com/2018/01/postgresql.png?w=150 150w, https://uhesse.files.wor

Licensed for Advanced Compression? Don’t forget the network

We often think of Advanced Compression being exclusively about compressing data “at rest”, ie, on some sort of storage device.  And don’t get me wrong, if we consider just that part of Advanced Compression, that still covers a myriad of opportunities that could yield benefits for your databases and database applications:

  • Heat maps
  • Automatic Data Optimization
  • XML, JSON and LOB compression (including de-duplication)
  • Compression on backups
  • Compression on Data Pump files
  • Additional compression options on indexes and tables
  • Compressed Flashback Data Archive storage
  • Storage snapshot compression

However, if you are licensed for the option, there are other things that you can also take advantage of when it comes to compression of data on the network.

Keep your orapw password file secure

This is a small demo I did when I’ve found a database password file (orapw) lying around in /tmp with -rw-rw-rw- permissions, to show how this is a bad idea. People think that the orapw file only contains hashes to validate a password given, and forget that it can be used to connect to a remote database without password.

I can easily imagine why the orapwd was there in /tmp. To build a standby database, you need to copy the password file to the standby server. If you don’t have direct access to the oracle user, but only a sudo access for ‘security reasons’, you can’t scp easily. Then you copy the file to /tmp, make it readable by all users, and you can scp with your user.

In this demo I don’t even have access to the host. I’ve only access to connect to a PDB with the SCOTT users, reated with utlsampl.sql, with those additional privileges, a read access on $ORACLE_HOME/dbs: