Linux Ask! is a Q & A web site specific for Linux related questions. Questions are collected, answered and audited by experienced Linux users.
Creates an index in MongoDB
Answer:
In an given collection, if you want to add an index on a specify field, you can do the following in the mongodb Interactive shell.
db.test.ensureIndex( { name : 1 } )
The key "name" from now on will have index enabled.
Show the storage used by a database in MySQL
Answer:
In previous article, we have already discussed how to list the database size in your MySQL server.
But if you want to have a more detail view on an individual database, you can try the following (crazy) SQL.
SELECT s.schema_name,
CONCAT(IFNULL(ROUND((SUM(t.data_length)+SUM(t.index_length))
/1024/1024,2),0.00),"Mb") total_size,
CONCAT(IFNULL(ROUND(((SUM(t.data_length)+SUM(t.index_length))-SUM(t.data_free))/1024/1024,2),0.00),"Mb")
data_used,
CONCAT(IFNULL(ROUND(SUM(data_free)/1024/1024,2),0.00),"Mb") data_free,
IFNULL(ROUND((((SUM(t.data_length)+SUM(t.index_length))-SUM(t.data_free))
/((SUM(t.data_length)+SUM(t.index_length)))*100),2),0) pct_used,
COUNT(table_name) total_tables
FROM INFORMATION_SCHEMA.SCHEMATA s
LEFT JOIN INFORMATION_SCHEMA.TABLES t ON s.schema_name = t.table_schema
WHERE s.schema_name = "mydatabase"
GROUP BY s.schema_name
ORDER BY pct_used DESC\GIt will give you something like the following..
schema_name: mydatabase
total_size: 165.09Mb
data_used: 12.09Mb
data_free: 153.00Mb
pct_used: 7.33
total_tables: 133Update an existing document in MongoDB
Answer:
In an given collection, if you want to perform update on an existing document, the easiest way is to use the following commands.
employee = db.employees.findOne( { name : "Peter" } );
employee.position = "Project Manager";
db.employees.save( employee );Done.
Remove a document in a collection in MongoDB
Answer:
If you want to remove a document in the test collection, with a key "name" equal to "Peter", you can execute the following command in the MongoDB Interactive Shell.
db.test.remove( { name : "Peter" } )
Done.
How to change the MySQL temporary directory
Answer:
To change the temporary directory of your MySQL server to use a non-default directory, you can change the tmpdir parameter in your my.cnf
..
tmpdir = /data/tmp
..Don't forget to change the permission of that temporary directory
# sudo chmod mysql:mysql /data/tmp
Then restart MySQL to take effect.
# /sbin/service mysqld restart
