MongoDB Replica Set High Availability Notes

MongoDB offers a strong solution for High Availability via the Replica Set High Availability setup. DBAs work with HA and become familiar with the behaviour during setup and management, there is also a requirement to communicate with application teams some of the HA behaviour. Developers can use this information to design their applications In the examples below - we are using a 3 node cluster set. A 3 node cluster replica set has a fault tolerance supporting unavailability of 1 node while still having a Primary Node and the ability to still write to the Primary. If 2 nodes become... Read more →

mongo : command not found

Question: I've installed the mongo as part of a replicaset . The server is part of a 3 - node replicaset and I can manage through MongoDB Operations Manager. But when i get onto the command line and type "mongo" , I'm getting the -bash: mongo: command not found. How can I fix this issue - as I'd like to be able to have the command line option Answer: Assuming everything is running as expected - the most likely reason is that the relevant mongo binaries are not in the /usr/bin folder. I've had this problem a few times and... Read more →

How to list MongoDB connections - client ip and port

Question: How can I list client ip , port and connection ID of connections to MongoDB? I want to connect through the MongoDB command line and extract this information as I'm testing some HA failover scenarios. Answer: There's a few different ways to extract the MongoDB connection details - for example you can use netstat. But from the command line - this syntax will report the details required db.currentOp(true).inprog.forEach(function(d){if(d.client)print(d.client, d.connectionId)}) Example output - clientip:port clientid: 127.0.0.1:55552 4668364 10.120.xxx.xxx:60942 4668363 10.120.xxx.xxx:60924 4668357 Read More on MongoDB How to read MongoDB system log file MongoDB cheatsheet Read more →

bash: /home/myuser/.ssh/authorized_keys: No such file or directory

Question: When I type in cat ~/.ssh/authorized_keys to a RHEL 7 server I get the following message: cat: /root/.ssh/authorized_keys: No such file or directory I'm going through the process of setting up a SSH to create a connection between BART and client Potgresql servers - to backup Postgresql databases. How can I fix this issue? Answer:You need to create the ssh directory for the first time and create the authorized keys file. Create the .ssh directory. First check if actually already exists mkdir ~/.ssh Set the right permissions for the new .ssh directory. Very important step chmod 700 ~/.ssh Create... Read more →

How to load csv data with quotes and ENCLOSED BY into MariaDB table

Question : I have a csv file , with 1 million rows and would like to import into a MariaDB table.I'm importing successfully but having a problem with a row where the "," is within a double quote. Example row: GenerationX,Rufus,Johnny,"Chat hype, Power crazy" i.e instead of getting 4 columns , I'm getting 5 , because the comma within the 4th column is splitting the data Could you give me an example of how to load the data and maintain the data integrity ? Answer: When loading data into a MariaDB table the optional : ENCLOSED BY can help you.... Read more →

MariaDB /tmp file filling with MAD file

Question: I've received an alert from a RHEL server with MariaDB installed. The alert refers to a MAD file filling the /tmp drive . What is going on? and how can I fix the mysql MAD file filling the /tmp drive? Answer: This is a common problem when under certain circumstances - CREATE & ALTER statements executed on InnoDB tables create a temporary table in mysql's tmpdir. To find out the current value check my.cnf or use SHOW VARIABLES LIKE "TMPDIR During the data load phase MariaDB creates a temporary table in /tmp - which consequently fills the /tmp The... Read more →

MariaDB Cheatsheet

--backup mysqldump -u myun -p MYPW > /mariadb/backups/mydb171117.sql --list indexes SHOW INDEX FROM mytable; --drop index DROP idx1 ON MYTABLE --list tables show tables; --list views SHOW FULL TABLES IN database_name WHERE TABLE_TYPE LIKE 'VIEW'; --list databases show databases; --drop database drop database db1; --show columns show columns FROM MYTABLE; --get index information SHOW INDEX FROM MYTABLE; mysqlshow -k db_name tbl_name --error log file SHOW VARIABLES LIKE 'log_error' tail xxxxx.err tail -f xxxxxx.err --show create table show create table MYTABLE --select version SHOW VARIABLES LIKE "%version%"; --find mariadb commands history find / -name .mysql_history --database collation SELECT COLLATION('myDB'); --or SELECT... Read more →

How to know PostgreSQL is running or installed

Question: How do I know if PostgreSQL is running or installed on a Linux server ? Answer: There are some ways to check whether PostgreSQL is running or installed, but it will depend on how PostgreSQL was installed . It pays to ask the user , how PostgreSQL was installed. Some different methods of PostgreSQL installation & configuration could include: -Installed from rpm packages and started by init script -Installed \ running but the installation is not associated to the default PATH or even the default port -Installed from rpm packages but not set to start As a starter these... Read more →

Notes on MongoDB BI Connector

These are my notes on installing the MongoDB BI Connector. The MongoDB Connector for Business Intelligence (BI) supports users to generate SQL queries against MongoDB databases. Typical client programs include Qlik,Tableau and Excel Details will depend on the overall architecture required. Typically I install MongoDB Connector on a dedicated server - to support wider usage ==Place the executable in /usr/bin mongodrdl mongosqld mongotranslate ==Place the cfg file in /usr/bin/mongobi - mongosqld.conf ===To start it from the command line mongosqld --mongo-uri "mongodb://MY_SERVER:27017" --auth --mongo-username MY_USER --mongo-password MY_PASSWORD --mongo-authenticationSource MY_AUTH_DB ===To start mongosqld with a configuration file (see example of basic configuration... Read more →

Top 10 Yoda tips for the Linux command line

Master these Linux commands and you will feel the Force or become the Linux Yoda . (or even just your job done more efficiently) I don't know anything about myprogram - how can I find out? 10 "info myprogram" or 9 "man myprogram" How can I find myprogram ? 8 "locate -i foo" or 7 "whereis foo" How can I view myprogram ? 6 "less foo" or 5 "emacs foo" How can I view the program's help ? This applies to most programs 4 myprogram "-h" or "--help" . How can I navigate further into a directory? 3 "cd ./mydirectory"... Read more →