Answer:

To install redis on Mac OSX using homebrew, use

# brew install redis

Answer:

A newer version of MySQL use upstart to autostart when system bootup, to disable it

# sudo mkdir /etc/init.disabled
# sudo mv /etc/init/mysql.conf /etc/init.disabled/

Answer:

You can use the following method to generate random string into a collection in MongoDB:

function randomString() { 
        var chars = 
"0123456789ABCDEFGHIJKLMNOPQRSTUVWXTZabcdefghiklmnopqrstuvwxyz"; 
        var randomstring = ''; 
        var string_length = 100;
        for (var i=0; i<string_length; i++) { 
                var rnum = Math.floor(Math.random() * chars.length); 
                randomstring += chars.substring(rnum,rnum+1); 
        } 
        return randomstring; 
} 

for(var i=0; i<2000000; i++){db.test.save({x:i, data:randomString()});} 

Answer:

In you mongo shell, execute the following command:

var sum = 0; db.getMongo().getDBs()["databases"].forEach(function(x) { sum += db.getMongo().getDB(x.name).stats().indexSize }); print(sum)

Answer:

To see how long a MongoDB instance was running, you can login into the mongo shell, and enter

db.serverStatus().uptime / 3600

The above command reply the value in term of hours.

Answer:

The easiest way is login into the MongoDB using the shell, enter the command:

db.adminCommand({getLog: "startupWarnings" })

Answer:

Simply type the following command in your MongoDB's shell

db.version()

Answer:

The easiest way is to install using the PPA approach.

# sudo add-apt-repository ppa:rwky/redis
# sudo apt-get update
# sudo apt-get install redis-server

That's it.

Answer:

To show the current privileges of a MySQL user, you can use the SHOW GRANTS statement

E.g.

mysql> SHOW GRANTS;

+----------------------------------------------------------------------------------------------------------------------------------------+
| Grants for root@localhost                                                                                                              |
+----------------------------------------------------------------------------------------------------------------------------------------+
| GRANT ALL PRIVILEGES ON *.* TO 'root'@'localhost' IDENTIFIED BY PASSWORD '*****************************************' WITH GRANT OPTION |
+----------------------------------------------------------------------------------------------------------------------------------------+

Answer:

Like in the shell, we can execute the command whoami to find out the current user name, we can use the function CURRENT_USER();

E.g.

mysql> SELECT CURRENT_USER();
+----------------+
| CURRENT_USER() |
+----------------+
| root@localhost |
+----------------+
1 row in set (0.00 sec)