Ilmar Kerm

Oracle, databases, Linux and maybe more

If you use Oracle database on NFS, make sure you use Oracle DirectNFS, which is a built in NFS client in Oracle database kernel. This makes it possible for the database software to access files on NFS share without calling the operating system kernel. The performance improvement is significant!

I use NFS a lot for Oracle databases, because it is so much easier to manage than any block device based system, specially when using Oracle RAC. Or when you need to clone the database.

And then one day I noticed that some Data Guard standby databases, rather large and busy ones, started to lag – more and more. Confusion started – why – same standby on another datacenter on same type of storage is completely fine. It was fine on this system also up to last week. What has changed? The long confusion part is not important… Until realised, that on the system that was working fine, Linux OS command nfsiostat (displaying Kernel level NFS statistics) – it showed hardly any traffic at all. But on the problematic system, nfsiostat displayed a very busy NFS traffic. The aha moment – DNFS! Linux kernel should not be able to see DNFS traffic.

When doing major OS upgrades, after you should also relink your Oracle database binaries:

Relinking Oracle Home FAQ ( Frequently Asked Questions) (Doc ID 1467060.1)

The note above even states that you should relink after every OS patch… So I just incuded relinking to the playbook that replaces database VM OS root disk. But since DNFS (probably other similar features too, like Unified Auditing??) needs to be linked into Oracle kernel separately – executing “relink all” silently disables DNFS.

Lets test. I’m using Oracle RDBMS 19.15.2, single instance. First I have DNFS enabled and working:

SQL> select id, svrname, dirname, nfsversion from v$dnfs_servers;

---------- ---------- --------------- ----------------
         1 /pt101          NFSv3.0

Then I shut down the database and execute relink all.

SQL> shu immediate
oracle$ lsnrctl stop
oracle$ umask 022 && $ORACLE_HOME/bin/relink all

Lets start up and see what happened.

SQL> startup mount
Database mounted.

SQL> alter database open;

Database altered.

SQL> select id, svrname, dirname, nfsversion from v$dnfs_servers;

no rows selected

And no DNFS! alert log is also missing the DNFS message:

Oracle instance running with ODM: Oracle Direct NFS ODM Library Version 6.0

Let shut it down and link DNFS back.

SQL> shu immediate

oracle$ cd $ORACLE_HOME/rdbms/lib && make -f dnfs_on

SQL> startup mount
SQL> select id, svrname, dirname, nfsversion from v$dnfs_servers;

---------- ---------- --------------- ----------------
         1 /pt101          NFSv3.0

And I have my precious DNFS back. So keep that in mind when you relink Oracle home binaries. Would be good to test if the same problem affects Unified Auditing.

Oracle recently released a thin driver for Python, meaning it does not require any Oracle client installation (like cx_Oracle does) and it is written natively in Python – one benefit of which is that it works on all platforms where Python is present, including ARM64.

You can read more about it here:

Interestingly it is not yet trivial to find examples, on how to use the new thin driver to connect to Oracle Autonomous Database.

By default Autonomous database requites mTLS connections, so first create and download the Instance wallet for your Autonomous database (zip file), do remember the password you set. Unzip and transfer ewallet.pem and tnsnames.ora to your Python host.

# Create directory for wallet files
$ mkdir wallet
$ pwd

# Transport ewallet.pem and tnsnames.ora to that directory
$ ls /home/ilmar/wallet/

If you have not yet done so, install the pythoin thin driver.

$ pip3.9 install --user oracledb
Collecting oracledb
  Downloading oracledb-1.1.1-cp39-cp39-manylinux_2_17_aarch64.manylinux2014_aarch64.whl (6.7 MB)
     |████████████████████████████████| 6.7 MB 24.1 MB/s 
Collecting cryptography>=3.2.1
  Downloading cryptography-38.0.1-cp36-abi3-manylinux_2_17_aarch64.manylinux2014_aarch64.manylinux_2_24_aarch64.whl (3.7 MB)
     |████████████████████████████████| 3.7 MB 34.9 MB/s 
Collecting cffi>=1.12
  Downloading cffi-1.15.1-cp39-cp39-manylinux_2_17_aarch64.manylinux2014_aarch64.whl (448 kB)
     |████████████████████████████████| 448 kB 90.9 MB/s 
Collecting pycparser
  Downloading pycparser-2.21-py2.py3-none-any.whl (118 kB)
     |████████████████████████████████| 118 kB 119.8 MB/s 
Installing collected packages: pycparser, cffi, cryptography, oracledb
Successfully installed cffi-1.15.1 cryptography-38.0.1 oracledb-1.1.1 pycparser-2.21

Connect from Python code to Autonomous database,

import oracledb, os

db = oracledb.connect(

with db.cursor() as c:
    for row in c.execute("SELECT owner, object_name FROM all_objects FETCH FIRST 10 ROWS ONLY"):



export ORACLE_USER=my_database_username
export ORACLE_PASSWORD=my_database_password
export ORACLE_TNS=connection_identifier_from_tnsnames.ora

$ python3.9 
('SYS', 'DUAL')

Here I used Oracle Linux 8 sever running on Ampere (ARM64) in Oracle Cloud Always Free Tier. No Oracle database client or Instantclient was installed.

Lets say your company has an automated system that propagates and renews TLS certificates for each server automatically, for example using NDES. And you want to use the same files also for your Oracle database TCPS protocol connections.

For Oracle database the database server user certificate needs to be placed inside Oracle wallet and the default workflow for Oracle wallet is that you create the private key and certificate request inside Oracle wallet and then use the exported certificate request to request a certificate from your certificate authority and then you import that certificate to the wallet.

But you have already issued certificate and private key as separate files, like many popular open source tools like it. It is possible to create Oracle wallet from these.

We have two files.

  • Private key – /etc/pki/tls/private/servername.key
  • Issued certificate – /etc/pki/tls/private/servername.crt

We also need the certificate authority certificates (all of them, the full chain) who issued your server certificate. You can usually download them from your CA webpage or there also might be URL embedded in the certificate itself.

I’m using orapki executable from 19c installation.

First create an empty Oracle wallet.

# orapki wallet create -wallet /oracle/wallet/location -pwd oracle_wallet_password

Then add all the certificate authority certificates to the wallet

# You can check the certificate if it has links to issuer server certificates embedded. You need to repeat that until there is no output (you have reached the root) and download each file along the way. Usually there are about 2-3 of them.
# openssl x509 -in /etc/pki/tls/private/servername.crt -inform pem -noout -issuer -ext authorityInfoAccess

# orapki wallet add -wallet /oracle/wallet/location -pwd oracle_wallet_password -trusted_cert -cert /tmp/ca_certificate_intermediate.cer
# orapki wallet add -wallet /oracle/wallet/location -pwd oracle_wallet_password -trusted_cert -cert /tmp/ca_certificate_root.cer

A quick sanity check, the server certificate you have should have TLS Web Server Authentication extended key usage set. If it is not, ask your CA to reissue the certificate. Without it your clients might get an error like this: IO error: extended key usage does not permit use for TLS server authentication 

# openssl x509 -ext extendedKeyUsage -in /etc/pki/tls/private/servername.crt -noout
X509v3 Extended Key Usage: 
    TLS Web Client Authentication, TLS Web Server Authentication

If the private key is unencrypted, then you first need to encrypt it in PKCS#8 format – into a separate temporary file. oraplki cannot import unencrypted private key.

# Check first, if the key in unencrypted
# head -1 /etc/pki/tls/private/servername.key

# export wallet_build_pass="long_key_encryption_password"
# openssl pkcs8 -topk8 -in /etc/pki/tls/private/servername.key -out /tmp/encrypted.key -passout env:wallet_build_pass

# Lets check that the resulting file has encrypted key
# # head -1 /tmp/encrypted.key 

Now you can import the private key and certificate into Oracle wallet.

# orapki wallet import_private_key -wallet /oracle/wallet/location -pwd oracle_wallet_password -pvtkeyfile /tmp/encrypted.key -pvtkeypwd long_key_encryption_password -cert /etc/pki/tls/private/servername.crt

Code – to automatically renew Oracle wallet. NB! read and modify the code according to your needs.

In Oracle Autonomous database one major application feature is missing – Flashback Data Archive. Purpose of that feature was archiving all data changes seamlessly to the application, no old-school trigger-based data archival/auditing needed. One major disadvantage of triggers is that end user session needs to wait for the trigger to execute, they become part of the end user transaction. FDA lets the users just declare for how long all changes need to be retained (even years) and it collected the data to be archived in the background, from UNDO data. It also had the possibility to add context from the user session that made the data change. Although FDA has been quite troublesome/buggy component, I’ve always liked its functionality.

FDA is part of all Oracle Database editions – except Oracle Autonomous Database. Reference

I currently do not see any other possibility than to go back to old-trigger based solutions, but how to make it as easy to maintain as possible? And keep the modification context.

Traditional way using triggers is to store :OLD (and :NEW ?) values in a separate table, while having a separate audit table for each source table. But these kinds of triggers need to be recreated (and history tables maintained also) whenever the source table structure changes. Sadly there is no way to serialize :OLD/:NEW or access them in any dynamic way.

There are ready made packages for implementing this style of auditing, for example this one by Connor McDonald.

I decided to create my own to make the maintenance much simpler. Store everything as JSON, and store only the new row version.

  • It is very easy to generate JSON object from a table row
  • I would argue, that there is no need to record :OLD row in the history, if :NEW is always recorded. And since every history record has a context attached, it makes more logical sense to me that you store the session context together with the :NEW row version – that this person changed the row to this new version. Not that this person removed that :OLD row version.
  • Changes to source table do not require any changes to triggers nor the history table.
  • Yes, JSON wastes more diskspace.
  • It is very easy to query JSON as relational data in Oracle.
  • Currently the code expects each table has a primary key named ID. I’m not going to change it to make it more generic, you are welcome to change the code for yourself 🙂 As always, don’t take the code blindly from the internet, understand it before you use it.