Repair and compact database in MongoDB
Answer:
To repair and compact a database in MongoDB, you can use the following command in the mongodb Interactive shell.
1. Select the database
use test
2. Repair the current database
db.repairDatabase()
Done.
Count the total number of objects in the collection in MongoDB
Answer:
In MongoDB, to count the total number of objects in the collection, you can use the following statement in the mongodb Interactive shell.
db.test.count()
The above statement will return the total number of objects in the collection "test"
Aug 152011
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.
