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Archive for August, 2020

Connecting Oracle database from PostgreSQL using Public DB Links.

Posted by FatDBA on August 31, 2020

Hi Guys,

This post is in continuation of my last post where I showed how to connect to Oracle database from an PostgreSQL instance. Last post was all about accessing Oracle database using Foreign data wrappers. This post is about accessing/querying Oracle database from PostgreSQL using DB Links.

Software Used:
Oracle Instant Clients (Need both BASIC and DEVEL packages)
Link: https://www.oracle.com/database/technologies/instant-client/linux-x86-64-downloads.html

For this method too, you have to install Oracle instant basic and devel packages.


[enterprisedb@fatdba ~]$ sudo rpm -Uvh oracle-instantclient12.2-basic-12.2.0.1.0-1.x86_64.rpm
[sudo] password for enterprisedb:
Preparing...                ########################################### [100%]
   1:oracle-instantclient12.########################################### [100%]
[enterprisedb@fatdba ~]$
[enterprisedb@fatdba ~]$ sudo rpm -Uvh oracle-instantclient12.2-devel-12.2.0.1.0-1.x86_64.rpm
Preparing...                ########################################### [100%]
   1:oracle-instantclient12.########################################### [100%]
[enterprisedb@fatdba ~]$

[enterprisedb@fatdba ~]$
[enterprisedb@fatdba ~]$ ls -ll /usr/lib/oracle/12.2/client64/lib
total 216568
lrwxrwxrwx. 1 root root        21 Aug 27 22:59 libclntshcore.so -> libclntshcore.so.12.1
-rw-rwxr--. 1 root root   8033199 Jan 26  2017 libclntshcore.so.12.1
lrwxrwxrwx. 1 root root        17 Aug 27 22:59 libclntsh.so -> libclntsh.so.12.1
-rw-rwxr--. 1 root root  71638263 Jan 26  2017 libclntsh.so.12.1
-rw-rwxr--. 1 root root   2981501 Jan 26  2017 libipc1.so
-rw-rwxr--. 1 root root    539065 Jan 26  2017 libmql1.so
-rw-rwxr--. 1 root root   6568149 Jan 26  2017 libnnz12.so
lrwxrwxrwx. 1 root root        15 Aug 27 22:59 libocci.so -> libocci.so.12.1
-rw-rwxr--. 1 root root   2218687 Jan 26  2017 libocci.so.12.1
-rw-rwxr--. 1 root root 124771800 Jan 26  2017 libociei.so
-rw-rwxr--. 1 root root    158543 Jan 26  2017 libocijdbc12.so
-rw-rwxr--. 1 root root    380996 Jan 26  2017 libons.so
-rw-rwxr--. 1 root root    116563 Jan 26  2017 liboramysql12.so
-rw-r--r--. 1 root root   3984814 Jan 26  2017 ojdbc8.jar
-rw-rwxr--. 1 root root    312974 Jan 26  2017 ottclasses.zip
-rw-r--r--. 1 root root     37494 Jan 26  2017 xstreams.jar
[enterprisedb@fatdba ~]$
 


Cool, let’s connect with the PostgreSQL instance and create the DBLink. To create that you need Oracle username and its password which you want to connect and its IP address along with SID or database name, and you are done. And yes, don’t forget to set the LD_LIBRARY_PATH to the location of your Oracle instant client.


[enterprisedb@fatdba ~]$ export LD_LIBRARY_PATH=/usr/lib/oracle/12.2/client64/lib
[enterprisedb@fatdba ~]$
[enterprisedb@fatdba ~]$ psql -d enterprisedb -U enterprisedb
psql.bin (10.12.20)
Type "help" for help.
enterprisedb=#
enterprisedb=#
enterprisedb=# select version();
                                                    version
---------------------------------------------------------------------------------------------------------------
 EnterpriseDB 10.12.20 on x86_64-pc-linux-gnu, compiled by gcc (GCC) 4.4.7 20120313 (Red Hat 4.4.7-23), 64-bit
(1 row)

enterprisedb=#
enterprisedb=# CREATE DATABASE LINK dixdroid CONNECT TO migr IDENTIFIED BY 'oracle90' USING oci '//10.0.0.130/fatdb';
CREATE DATABASE LINK
enterprisedb=#
 


Great, now time to test. Lets do a query on Oracle’s table from Postgresql instance using DB Link named ‘dixdroid’ which we have created earlier.



enterprisedb=# select * from migr.bigtab1@dixdroid;
  id  |    created_date    | lookup_id |            data
------+--------------------+-----------+----------------------------
  320 | 19-MAY-19 02:10:38 |         1 | This is some data for 320
  321 | 19-MAY-18 02:10:38 |         2 | This is some data for 321
  322 | 19-MAY-19 02:10:38 |         1 | This is some data for 322
  323 | 19-MAY-20 02:10:38 |         3 | This is some data for 323
  324 | 19-MAY-18 02:10:38 |         2 | This is some data for 324
  325 | 19-MAY-20 02:10:38 |         3 | This is some data for 325
  326 | 19-MAY-19 02:10:38 |         1 | This is some data for 326
  327 | 19-MAY-18 02:10:38 |         2 | This is some data for 327
  328 | 19-MAY-19 02:10:38 |         1 | This is some data for 328
  329 | 19-MAY-20 02:10:38 |         3 | This is some data for 329
  330 | 19-MAY-18 02:10:38 |         2 | This is some data for 330
  331 | 19-MAY-20 02:10:38 |         3 | This is some data for 331
 

Great, it worked like a charm!

Hope It Helps
Prashant Dixit

Posted in Basics | Tagged: , | 1 Comment »

Connecting Oracle database from PostgreSQL using ORACLE_FDW (Foreign Data Wrappers)

Posted by FatDBA on August 27, 2020

Hi All,

Today when I received a call from my team mate where he was facing issues with PostgreSQL when trying to access a remote table that exists on an Oracle database, I I instantly recalled something similar I tried few years back using Oracle Foreign Data Wrappers (oracle_FDW). So, I tried to perform a quick demo showing steps on how to do that using FDW.

Source: EnterpriseDB 10.12.20 on x86_64-pc-linux-gnu
Target: Oracle Enterprise 12c Release 2 (12.2.0.1.0)

Software Used:
Oracle Instant Clients (Need both BASIC and DEVEL packages)
Link: https://www.oracle.com/database/technologies/instant-client/linux-x86-64-downloads.html

Oracle FDW Software: Version 2.2.1)
Link: https://pgxn.org/dist/oracle_fdw/2.2.1/

Below are the files that I have downloaded.


-rw-rw-r--.  1 enterprisedb enterprisedb 143K Aug 27 17:12 oracle_fdw-2.2.1.zip
-rw-rw-r--.  1 enterprisedb enterprisedb  51M Aug 27 17:26 oracle-instantclient12.2-basic-12.2.0.1.0-1.x86_64.rpm
-rw-rw-r--.  1 enterprisedb enterprisedb 593K Aug 27 17:27 oracle-instantclient12.2-devel-12.2.0.1.0-1.x86_64.rpm
drwxrwxr-x.  5 enterprisedb enterprisedb 4.0K Aug 27 22:43 oracle_fdw-2.2.1

[enterprisedb@fatdba ~]$
[enterprisedb@fatdba ~]$
 


Let’s install both if the two instant clients on the server.


[enterprisedb@fatdba ~]$ sudo rpm -Uvh oracle-instantclient12.2-basic-12.2.0.1.0-1.x86_64.rpm
[sudo] password for enterprisedb:
Preparing...                ########################################### [100%]
   1:oracle-instantclient12.########################################### [100%]
[enterprisedb@fatdba ~]$
[enterprisedb@fatdba ~]$
[enterprisedb@fatdba ~]$ sudo -Uvh oracle-instantclient12.2-devel-12.2.0.1.0-1.x86_64.rpm
sudo: unknown user: vh
[enterprisedb@fatdba ~]$ sudo rpm -Uvh oracle-instantclient12.2-devel-12.2.0.1.0-1.x86_64.rpm
Preparing...                ########################################### [100%]
   1:oracle-instantclient12.########################################### [100%]
[enterprisedb@fatdba ~]$
[enterprisedb@fatdba ~]$
[enterprisedb@fatdba ~]$
 


now let’s quickly check if all required libraries are created.


[oracle@fatdba client64]$ cd lib/
[oracle@fatdba lib]$ pwd
/usr/lib/oracle/12.2/client64/lib
[oracle@fatdba lib]$
[oracle@fatdba lib]$
[oracle@fatdba lib]$ ls -ll
total 216568
lrwxrwxrwx. 1 root root        21 Aug 27 22:59 libclntshcore.so -> libclntshcore.so.12.1
-rw-rwxr--. 1 root root   8033199 Jan 26  2017 libclntshcore.so.12.1
lrwxrwxrwx. 1 root root        17 Aug 27 22:59 libclntsh.so -> libclntsh.so.12.1
-rw-rwxr--. 1 root root  71638263 Jan 26  2017 libclntsh.so.12.1
-rw-rwxr--. 1 root root   2981501 Jan 26  2017 libipc1.so
-rw-rwxr--. 1 root root    539065 Jan 26  2017 libmql1.so
-rw-rwxr--. 1 root root   6568149 Jan 26  2017 libnnz12.so
lrwxrwxrwx. 1 root root        15 Aug 27 22:59 libocci.so -> libocci.so.12.1
-rw-rwxr--. 1 root root   2218687 Jan 26  2017 libocci.so.12.1
-rw-rwxr--. 1 root root 124771800 Jan 26  2017 libociei.so
-rw-rwxr--. 1 root root    158543 Jan 26  2017 libocijdbc12.so
-rw-rwxr--. 1 root root    380996 Jan 26  2017 libons.so
-rw-rwxr--. 1 root root    116563 Jan 26  2017 liboramysql12.so
-rw-r--r--. 1 root root   3984814 Jan 26  2017 ojdbc8.jar
-rw-rwxr--. 1 root root    312974 Jan 26  2017 ottclasses.zip
-rw-r--r--. 1 root root     37494 Jan 26  2017 xstreams.jar
[oracle@fatdba lib]$
 


Yup, they all are there, perfect!
Now lets set the installation library path using variable LD_LIBRARY_PATH, same as below.
This is to avoid errors i.e.

ERROR:  could not load library "/opt/edb/as10/lib/oracle_fdw.so": libclntsh.so.12.1: cannot open shared object file: No such file or directory 


[enterprisedb@fatdba oracle_fdw-2.2.1]$
[enterprisedb@fatdba oracle_fdw-2.2.1]$
[enterprisedb@fatdba oracle_fdw-2.2.1]$ export LD_LIBRARY_PATH=/usr/lib/oracle/12.2/client64/lib
[enterprisedb@fatdba oracle_fdw-2.2.1]$
 


Now let’s do a quick restart of the postgresql instance.


[enterprisedb@fatdba oracle_fdw-2.2.1]$
[enterprisedb@fatdba oracle_fdw-2.2.1]$ pg_ctl -D /opt/edb/as10/data restart -m fast
waiting for server to shut down.... done
server stopped
waiting for server to start....2020-08-27 23:06:33 CEST [3641]: [1-1] user=,db=,remote= LOG:  listening on IPv4 address "0.0.0.0", port 5444
2020-08-27 23:06:33 CEST [3641]: [2-1] user=,db=,remote= LOG:  listening on IPv6 address "::", port 5444
2020-08-27 23:06:33 CEST [3641]: [3-1] user=,db=,remote= LOG:  listening on Unix socket "/tmp/.s.PGSQL.5444"
2020-08-27 23:06:33 CEST [3641]: [4-1] user=,db=,remote= LOG:  redirecting log output to logging collector process
2020-08-27 23:06:33 CEST [3641]: [5-1] user=,db=,remote= HINT:  Future log output will appear in directory "custompg_logdir".
 done
server started
[enterprisedb@fatdba oracle_fdw-2.2.1]$
[enterprisedb@fatdba oracle_fdw-2.2.1]$
[enterprisedb@fatdba oracle_fdw-2.2.1]$ psql -d enterprisedb -U enterprisedb
psql.bin (10.12.20)
Type "help" for help.
 


All good, lets created the EXTENSION in postgresql.


enterprisedb=#
enterprisedb=#
enterprisedb=# create extension oracle_fdw;
CREATE EXTENSION
enterprisedb=#
 


Now next will create the foreign server for the remote database which I need to connect to, Oracle 12.2 in my case.
Note: Here 10.0.0.130 is the oracle_server machine IP address where Oracle is running and ‘fatdb’ is the instance name.


enterprisedb=#
enterprisedb=#
enterprisedb=#
enterprisedb=# create server oracle foreign data wrapper oracle_fdw options (dbserver '//10.0.0.130/fatdb' );
CREATE SERVER
enterprisedb=#
 


Next is to create the USER MAPPING for the specific user which I would like to access, in my case it was ‘migr’ user, and finally pass the password of the user.


enterprisedb=# create user mapping for enterprisedb server oracle options (user 'migr', password 'oracle90');
CREATE USER MAPPING
enterprisedb=#
enterprisedb=#
 


All set, you can now try to query the remote table.


enterprisedb=#
enterprisedb=# select * from migr.bigtab1;
  id  |    created_date    | lookup_id |            data
------+--------------------+-----------+----------------------------
  320 | 19-MAY-19 02:10:38 |         1 | This is some data for 320
  321 | 19-MAY-18 02:10:38 |         2 | This is some data for 321
  322 | 19-MAY-19 02:10:38 |         1 | This is some data for 322
  323 | 19-MAY-20 02:10:38 |         3 | This is some data for 323
  324 | 19-MAY-18 02:10:38 |         2 | This is some data for 324
  325 | 19-MAY-20 02:10:38 |         3 | This is some data for 325
  326 | 19-MAY-19 02:10:38 |         1 | This is some data for 326
  327 | 19-MAY-18 02:10:38 |         2 | This is some data for 327
  328 | 19-MAY-19 02:10:38 |         1 | This is some data for 328
  329 | 19-MAY-20 02:10:38 |         3 | This is some data for 329
  330 | 19-MAY-18 02:10:38 |         2 | This is some data for 330
  331 | 19-MAY-20 02:10:38 |         3 | This is some data for 331
  332 | 19-MAY-19 02:10:38 |         1 | This is some data for 332
 


Let’s do some more fun, lets try to do one insertion.


enterprisedb=#
enterprisedb=# select count(*) from migr.bigtab1;
 count
-------
  1000
(1 row)

enterprisedb=# insert into migr.bigtab1 values(1001, '19-MAY-19 02:10:38', 4, 'This is some data for prashant');
INSERT 0 1
enterprisedb=# select count(*) from migr.bigtab1;
 count
-------
  1001
(1 row)

enterprisedb=# select * from migr.bigtab1 where id=1001;
  id  |    created_date    | lookup_id |              data
------+--------------------+-----------+--------------------------------
 1001 | 19-MAY-19 02:10:38 |         4 | This is some data for prashant
(1 row)

enterprisedb=#
enterprisedb=#
 

Hope It Helps
Prashant Dixit

Posted in Advanced | Tagged: | 1 Comment »

Datastax Certified Cassandra Administrator, some tips & more

Posted by FatDBA on August 21, 2020

Hi Guys,

With a sharp rise in NoSQL databases, many of the organizations are making a transition from traditional databases to distributed and high performance databases like ‘Cassandra’. Cassandra has become Apache’s one of the most popular projects. Though there are multiple NoSQL databases available in the market but no one has the features like peer-to-peer architecture, HA and Fault tolerant, Column based, Highly perform-ant, Schema Less, tunable consistency, great analytical possibilities, easy to scale-up & scale-down, distributed and the list goes on and on and on.

Cassandra already proved it’s mettle and is magical for IoT, Sensor data, Event based, Time series data, voucher generation systems and with other data models. Datastax provides best in class database management software and wide-range services with 24×7 support to get more from your Cassandra. Alongside comes some really cool features and tools i.e. opscenter (GUI), Nodesync (for enti entropy repairs), great SOLR integration, dsetool (similar to nodetool with more capabilities), sstableloader, pre-flight check tool, yaml file compare tools, stress tools, extra commands i.e. dsefs and many more.

DataStax is a pioneer and they have their own Cassandra certification path/track to prove you have valid credentials to work with Cassandra database either as a developer or an administrator. Now question comes where to start ?? – In fact many of you have asked me about my latest credentials ‘Datastax Apache Cassandra 3.x Administrator Associate‘, I was getting questions like how to prepare, how to book the exam and many other related questions. So, this post will be all about covering topics like how to prepare and book exam along with few tips.

I would always prefer to go point wise to make things more ordered and easy to digest.

1. Create your account on Datastax Academy.
Link: https://auth.cloud.datastax.com/auth/realms/CloudUsers/login-actions/registration?client_id=absorb&tab_id=lv4-57nRbu4

2. Go to the option ‘Catalog’ to lookout for courses available.
You have to choose between the Administrator (3 course based curriculum) or Developer (3 Courses based curriculum) track. I have completed the ADMIN path and it has three courses DS101 (Introduction), DS201 (Foundations) and DS210 (Operations with Apache Cassandra). All of the courses are beautifully designed, contains large numbers of demos, presentations, guides, quiz and a pre-build Ubuntu VM where you can all exercises.

Though the presentations and program covers every topic and all major parameters and topics but still if you want to read in depth, they have their own document collection and can be accessed through their website https://docs.datastax.com/en/landing_page/doc/landing_page/current.html or from https://cassandra.apache.org/doc/latest/

Note: There are few other specialized courses available too within the catalog i.e. Kafka connectors, DSE Graph, DSE Analytics, DSE Search etc.

3. Other learning platforms
Github: https://github.com/datastax
Can be very useful specially if you are preparing for developer track.
Youtube: Full of some great presentations, videos and some precious workshops and demos.
https://www.youtube.com/user/DataStaxMedia
Twitter: For news (about webinars etc.), press releases and other exciting information.
https://twitter.com/DataStax (@DataStax)

4. All set!
Once you are done with your all three of your courses under ADMIN track, you are done and ready for the certification. Go to ‘Datastax Certification’ widget within catalog and book your exam by creating your profile on their certification website.
https://certification.mettl.com/datastax/applicant/signup

Currently they are giving one free exam vouchers and those will be issued at the end of the series for participants of the workshop.

5. Once registered you have to choose your exam type – Admin or Developer.
Both of the exams has 60 questions that you have to complete within 90 minutes, exam fees (right now) is $145
Note: It’s good that you check your system comparability before the exam, for more details follow their official guidelines.

So, don’t wait, go and enroll for the course and grab a chance for giving free certification and more importantly stand out from the crowd. These widely accepted and recognized credentials will help you in your continued professional development and is an ideal way to gain a greater understanding of your industry, and to enhance your knowledge and skills. It also offers excellent chances to network among Cassandra geeks.

Hope It Helps!
Prashant Dixit

Posted in Basics, Uncategorized | Tagged: | Leave a Comment »

Passed ‘Datastax Apache Cassandra 3.x Administrator Associate’ Certification

Posted by FatDBA on August 21, 2020

Hi Guys,

News to share, today itself I’ve cleared the ‘Datastax Apache Cassandra 3.x Administrator Associate‘ Certification. Was working towards Cassandra from past few months now, and it’s always good to get certified from the market leaders. Good way to stand out from the crowd!

Will soon write a blog about the preparation and the process to get certified from Datastax, stay tuned!

Hope It Helps!
Prashant D

Posted in Basics | Tagged: | Leave a Comment »

Cassandra node refused to start – MismatchedInputException: No content to map due to end-of-input

Posted by FatDBA on August 5, 2020

Hi All,

This one will be a quick one, kind of error and solution approach.
This time it’s about Cassandra statup error which I have faced while doing some testing on a POC box and how I resolved it.

In this case I was using Datastax Cassandra 6.8.1 on RHEL6, I tried starting the instance but failed with error which says “MismatchedInputException: No content to map due to end-of-input”.
I’ve attempted to start it few more times but ended up with the same error message. Below is the complete/full error details.


WARN  [main] 2020-08-05 13:43:46,277  DatabaseDescriptor.java:1517 - JMX is not enabled to receive remote connections. Please see cassandra-env.sh for more info.
INFO  [main] 2020-08-05 13:43:46,281  DseDelegateSnitch.java:39 - Setting my workloads to [Cassandra]
INFO  [main] 2020-08-05 13:43:46,358  YamlConfigurationLoader.java:77 - Configuration location: file:/home/cassandra/dse-6.8.1_node1/resources/cassandra/conf/cassandra.yaml
INFO  [main] 2020-08-05 13:43:46,360  DseDelegateSnitch.java:41 - Initialized DseDelegateSnitch with workloads [Cassandra], delegating to com.datastax.bdp.snitch.DseSimpleSnitch
INFO  [main] 2020-08-05 13:43:46,424  YamlConfigurationLoader.java:77 - Configuration location: file:/home/cassandra/dse-6.8.1_node1/resources/cassandra/conf/cassandra.yaml
ERROR [main] 2020-08-05 13:43:47,904  DseModule.java:126 - Unable to start server. Exiting...
org.apache.cassandra.io.FSReadError: com.fasterxml.jackson.databind.exc.MismatchedInputException: No content to map due to end-of-input
 at [Source: (BufferedInputStream); line: -1, column: 0]
        at com.datastax.bdp.db.nodes.Nodes.transactionalRead(Nodes.java:195)
        at com.datastax.bdp.db.nodes.Nodes.access$100(Nodes.java:76)
        at com.datastax.bdp.db.nodes.Nodes$Local.(Nodes.java:477)
        at com.datastax.bdp.db.nodes.Nodes.(Nodes.java:97)
        at com.datastax.bdp.db.nodes.Nodes$Instance.setup(Nodes.java:911)
        at org.apache.cassandra.config.DatabaseDescriptor.applyMetadata(DatabaseDescriptor.java:587)
        at org.apache.cassandra.config.DatabaseDescriptor.daemonInitialization(DatabaseDescriptor.java:234)
        at org.apache.cassandra.config.DatabaseDescriptor.daemonInitialization(DatabaseDescriptor.java:249)
        at com.datastax.bdp.DseCoreModule.(DseCoreModule.java:84)
        at com.datastax.bdp.DseModule.getRequiredModules(DseModule.java:163)
        at com.datastax.bdp.server.AbstractDseModule.configure(AbstractDseModule.java:27)
        at com.datastax.bdp.DseModule.configure(DseModule.java:89)
        at com.google.inject.AbstractModule.configure(AbstractModule.java:62)
        at com.google.inject.spi.Elements$RecordingBinder.install(Elements.java:340)
        at com.google.inject.spi.Elements.getElements(Elements.java:110)
        at com.google.inject.internal.InjectorShell$Builder.build(InjectorShell.java:138)
        at com.google.inject.internal.InternalInjectorCreator.build(InternalInjectorCreator.java:104)
        at com.google.inject.Guice.createInjector(Guice.java:96)
        at com.google.inject.Guice.createInjector(Guice.java:73)
        at com.google.inject.Guice.createInjector(Guice.java:62)
        at com.datastax.bdp.ioc.DseInjector.get(DseInjector.java:36)
        at com.datastax.bdp.DseModule.main(DseModule.java:103)
Caused by: com.fasterxml.jackson.databind.exc.MismatchedInputException: No content to map due to end-of-input
 at [Source: (BufferedInputStream); line: -1, column: 0]
 


Now, let’s talk about the fix that I have applied to get rid of the problem, but before that I recalled that the database was abruptly shutdown last time due to server/hsot crashed. This file contains local startup information like data center, release info, scheam version, native transport address, port info (JMX, storage etc.), broadcast address etc.


[cassandra@fatdba-doccass bin]$ cd /var/lib/cassandra/metadata/nodes/
[cassandra@fatdba-doccass nodes]$ ls
local  peers  snapshots
[cassandra@fatdba-doccass nodes]$ rm -rf local
[cassandra@fatdba-doccass nodes]$
[cassandra@fatdba-doccass nodes]$
[cassandra@fatdba-doccass nodes]$ ls -ltrh
total 4.0K
drwxrwxr-x. 2 cassandra cassandra 6 Jul 27 16:07 snapshots
-rw-rw-r--. 1 cassandra cassandra 1 Aug  4 18:29 peers
 

Now let’s try to start the node once again.


[cassandra@fatdba-doccass bin]$
[cassandra@fatdba-doccass bin]$ ./dse cassandra
 


And it got started after clearning the local details/information which was there when node was crashed.

Hope It Helps
Prashant Dixit

Posted in Advanced, troubleshooting | Tagged: , | Leave a Comment »

 
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