Sunday, April 9, 2017

Accessing Oracle tables via MariaDB CONNECT engine and ODBC

In my previous working environment it was typical to consider MariaDB Server as just a set of "random" storage engines mixed together, sometimes for unclear reasons and with questionable extra value. But even at that times I was already impressed by some features of one of the engines supported only by MariaDB, CONNECT. PIVOT table type specifically was of interest in a couple of customer cases I had to work on, but I quickly found out that the engine does not work with Oracle's MySQL or Percona Server, and thus had to forget about it for some time.

Recently while working in MariaDB I've got several more chances to deal with some new CONNECT use cases (and some related problems, that ended up mostly minor or caused by ignorance). This engine can be (and is, widely) used to access tables from virtually any other database management system or data source, as long as there is an ODBC or JDBC driver for it. I had to set up a testing environment to reproduce some of the problems noted while accessing remote tables in Oracle RDBMS, and eventually decided to document setup steps, mistakes and findings for myself and my readers.

I think the topic may require a series of posts, and in this first one I plan to concentrate on creating a basic testing environment to access Oracle RDBMS via ODBC driver and CONNECT engine on my main testing box running Fedora 25, and resolving simplest access issues, like those I described in MDEV-12355 (ended as not a bug thanks to quick help and clarifications from engine creator, Olivier Bertrand).

For pure testing purposes I had not planned to spend time installing and setting up Oracle RDBMS on that Fedora 25 box directly (later I tried and failed), but decided to rely on some existing Docker image. So, I started with installing Docker and dependencies (see this article for some hints, if needed):
[openxs@fc23 ~]$ sudo dnf install docker
  container-selinux.noarch 2:2.10-1.fc25
  docker.x86_64 2:1.12.6-6.gitae7d637.fc25
  docker-common.x86_64 2:1.12.6-6.gitae7d637.fc25
  oci-register-machine.x86_64 0-2.7.gitbb20b00.fc25
  oci-systemd-hook.x86_64 1:0.1.6-1.gitfe22236.fc25


[openxs@fc23 ~]$ sudo systemctl start docker
I am going to skip details on images that had not worked well (not a topic for this blog). Eventually I ended up working with
[openxs@fc23 server]$ sudo docker run -d -p 8080:8080 -p 1521:1521 -e ORACLE_ALLOW_REMOTE=true sath89/oracle-12c:latest
[openxs@fc23 server]$ sudo docker ps
CONTAINER ID        IMAGE                      COMMAND             CREATED             STATUS              PORTS                                            NAMES
4515bc4a6fb4        sath89/oracle-12c:latest   "/ "   14 seconds ago      Up 8 seconds>1521/tcp,>8080/tcp   adoring_turing

[openxs@fc23 server]$ sudo docker logs -f 4515bc4a6fb4
ls: cannot access /u01/app/oracle/oradata: No such file or directory
Database not initialized. Initializing database.
Starting tnslsnr
Copying database files
1% complete
3% complete
11% complete
18% complete
26% complete
37% complete
Creating and starting Oracle instance
40% complete
45% complete
50% complete
55% complete
56% complete
60% complete
62% complete
Completing Database Creation
66% complete
70% complete
73% complete
85% complete
96% complete
100% complete
Look at the log file "/u01/app/oracle/cfgtoollogs/dbca/xe/xe.log" for further details.
Configuring Apex console
Database initialized. Please visit http://#containeer:8080/em http://#containeer:8080/apex for extra configuration if needed
Starting web management console
PL/SQL procedure successfully completed.
Starting import from '/docker-entrypoint-initdb.d':
found file /docker-entrypoint-initdb.d//docker-entrypoint-initdb.d/*
[IMPORT] / ignoring /docker-entrypoint-initdb.d/*
Import finished
Database ready to use. Enjoy! ;)
This image initializes new database by default (unless you pass a volume on host, then it is initialized for the first time if the database is not there), so you have to wait (maybe for many minutes) and check the logs before trying to access the database. Note that container's port 1521 is mapped to host's port 1521 (and my Fedora 25 IP address,, is then used later below to access "remote" Oracle server on this port).

So, my "Oracle server" is ready (probably). Now, my Fedora 25 host will work as a client, so I had downloaded and installed basic Oracle client software RPMs (including ODBC driver and SQL*Plus) from OTN:
[openxs@fc23 maria10.1]$ rpm -q -a | grep oracle
I also installed unixODBC (including -devel, as I built MariaDB from source and one needs unixODBC-devel to have CONNECT engine build properly) as fine manual stated at the beginning:
[openxs@fc23 maria10.1]$ rpm -q -a | grep unixODBC
One has to set up tnsnames.ora for Oracle client to work with (remote) instance, and /etc/odbcinst.ini + /etc/odbc.ini to inform unixODBC about the known drivers and system data sources (this discussion had some useful hints):
[openxs@fc23 maria10.1]$ cat /etc/oracle/tnsnames.ora
XE =
  (Host =
  (Port = 1521)

[openxs@fc23 maria10.1]$ cat /etc/odbcinst.ini

Description = Oracle ODBC driver for Oracle 11g
Driver64 = /usr/lib/oracle/11.2/client64/lib/
FileUsage = 1
Driver Logging = 7

[openxs@fc23 maria10.1]$ cat /etc/odbc.ini
Driver = OracleODBCDSN = OracleODBC
ServerName = XE
UserID = system
Password = oracle
 Surely, I tried to access my Oracle server in Docker container via sqlplus command first:
[openxs@fc23 server]$ /usr/lib/oracle/11.2/client64/bin/sqlplus system/oracle@localhost:1521/ error while loading shared libraries: cannot open shared object file: No such file or directory
[openxs@fc23 server]$ ldd /usr/lib/oracle/11.2/client64/bin/sqlplus (0x00007ffe8813b000) => not found => not found => not found => /lib64/ (0x00007f0aadc93000) => /lib64/ (0x00007f0aad98a000) => /lib64/ (0x00007f0aad76a000) => /lib64/ (0x00007f0aad551000) => /lib64/ (0x00007f0aad18b000)
        /lib64/ (0x0000563b14bfb000)
This is what happens when one does not care to read all the details and forgets to set some environment variables and inform dynamic loader about libraries location. So, I did the following to resolve the problem:
[openxs@fc23 server]$ export ORACLE_HOME=/usr/lib/oracle/11.2/client64
[openxs@fc23 server]$ export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:$ORACLE_HOME/lib
[openxs@fc23 server]$ export PATH=$PATH:$ORACLE_HOME/bin
[openxs@fc23 server]$ sudo ldconfig
[openxs@fc23 server]$ ldd /usr/lib/oracle/11.2/client64/bin/sqlplus (0x00007ffd31b50000) => /usr/lib/oracle/11.2/client64/lib/ (0x00007f88f680f000) => /usr/lib/oracle/11.2/client64/lib/ (0x00007f88f3ea0000) => /usr/lib/oracle/11.2/client64/lib/ (0x00007f88f3ad3000) => /lib64/ (0x00007f88f38b2000) => /lib64/ (0x00007f88f35a9000) => /lib64/ (0x00007f88f3389000) => /lib64/ (0x00007f88f3170000) => /lib64/ (0x00007f88f2daa000) => /lib64/ (0x00007f88f2ba8000)
        /lib64/ (0x000056123639a000)

[openxs@fc23 server]$ sqlplus system/oracle@localhost:1521/    
SQL*Plus: Release Production on Fri Mar 24 11:00:21 2017

Copyright (c) 1982, 2013, Oracle.  All rights reserved.

Connected to:
Oracle Database 12c Standard Edition Release - 64bit Production

SQL> select count(*) from scott.emp;


SQL> create table scott.t1(c1 number(30));

Table created.

SQL> insert into scott.t1 values (12345);

1 row created.

SQL> desc scott.t1;
 Name                                      Null?    Type
 ----------------------------------------- -------- ----------------------------
 C1                                                 NUMBER(30)


SQL> exit
Disconnected from Oracle Database 12c Standard Edition Release - 64bit Production
So, SQL*Plus (that I still miss sometimes, after using it maybe only 10 times over last 12 years) client works. Let's try to access Oracle via ODBC and isql now:
[openxs@fc23 server]$ isql -v oracle
[08004][unixODBC][Oracle][ODBC][Ora]ORA-12154: TNS:could not resolve the connect identifier specified

[ISQL]ERROR: Could not SQLConnect
Surely, one more environment variable is not set, the one pointing out the location of tnsnames.ora file:
[openxs@fc23 server]$ export TNS_ADMIN=/etc/oracle
[openxs@fc23 server]$ isql -v oracle
| Connected!                            |
|                                       |
| sql-statement                         |
| help [tablename]                      |
| quit                                  |
|                                       |
SQL> select * from scott.t1;
| C1                              |
| 12345                           |
SQLRowCount returns -1
1 rows fetched
SQL> select count(*) from scott.emp;+-----------------------------------------+
| COUNT(*)                                |
| 14                                      |
SQLRowCount returns -1
1 rows fetched
SQL> quit
[openxs@fc23 server]$

Looks like now we should be able to use ODBC table type of CONNECT storage engine of MariaDB (that was already loaded with INSTALL SONAME ''; check the details here) to access remote Oracle table:
MariaDB [test]> create table oracle_t1 engine=connect table_type=ODBC tabname='t1' dbschema='scott' connection='dsn=oracle';
ERROR 1105 (HY000): Cannot get columns from t1
MariaDB [test]> show warnings\G
*************************** 1. row ***************************
  Level: Error
   Code: 1105
Message: Cannot get columns from t1
*************************** 2. row ***************************
  Level: Error
   Code: 1030
Message: Got error 122 "Internal (unspecified) error in handler" from storage engine CONNECT
2 rows in set (0.00 sec)
Do not be like me and do not report bugs when you see these messages! Go read the fine manual that explicitly mentions Oracle as being case sensitive and converting identifiers to upper case unless they are quoted.

As soon as you use proper case in tabname (and dbname) settings, everything works as expected, at least for my primitive use case:
MariaDB [test]> create table t1_oracle engine=connect table_type=ODBC tabname='t1' dbname='scott' connection='dsn=oracle';
ERROR 1105 (HY000): Cannot get columns from t1
MariaDB [test]> create table t1_oracle engine=connect table_type=ODBC tabname='T1' dbname='scott' connection='dsn=oracle';ERROR 1105 (HY000): Cannot get columns from T1
MariaDB [test]> create table t1_oracle engine=connect table_type=ODBC tabname='T1' dbname='SCOTT' connection='dsn=oracle';Query OK, 0 rows affected (1.29 sec)

MariaDB [test]> select * from t1_oracle;
| C1    |
| 12345 |
1 row in set (0.07 sec)

MariaDB [test]> create table t2_oracle engine=connect table_type=ODBC tabname='SCOTT.T1' connection='dsn=oracle';
Query OK, 0 rows affected (3.54 sec)

MariaDB [test]> select * from t2_oracle;
| C1    |
| 12345 |
1 row in set (0.06 sec)
To summarize, with some initial setup efforts (that should include reading the official CONNECT manual) it is easy to access Oracle tables from MariaDB server via ODBC driver. It may be very useful if you plan to migrate or use some data from Oracle RDBMS.

As a side note, Docker really rocks sometimes. I spent maybe 15+ years installing Oracle RDBMS (starting from version 7.0.16 or so) on all kinds of OSes dozens of times, and I do not miss this experience and do not mind to have it up and running with one simple command any time (rarely) I need it.

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