How do you use Journaling for write concern in MongoDB

Question

With the help of code can you tell me How do you use Journaling for write concern in MongoDB?

Answer 1

Using Journaling for Write Concern in MongoDB

Journaling is a mechanism in MongoDB that helps ensure data durability by writing changes to a journal file before applying them to the actual database files. This protects against unexpected crashes and power failures.

How Journaling Works

MongoDB writes operations to an in-memory buffer.

These operations are then written to a journal file before they are applied to the actual database storage.

If MongoDB crashes before committing changes to disk, the journal file is used to recover the data on restart.

Configuring Write Concern with Journaling

Write concern in MongoDB specifies the level of acknowledgment required for write operations. You can configure it to use journaling for durability.

1. Using j: true in Write Concern

You can explicitly enable journaling in write operations by setting { j: true } in the write concern.

Example: Ensuring Data is Written to the Journal

db.users.insertOne(

   { name: "Ram", age: 23 },

   { writeConcern: { j: true } }

)

2. Using Journaling in w and j Together

You can combine replication (w) and journaling (j) to increase reliability.

Example: Write Acknowledged After Journal and One Replica Confirmation

db.orders.insertOne(

   { item: "Laptop", price: 1000 },

   { writeConcern: { w: 2, j: true } }

)

3. Enabling Journaling at Server Level

By default, journaling is enabled in MongoDB when running with the WiredTiger storage engine.

To check if journaling is enabled, run:

db.serverStatus().storageEngine

It should return:

{

  "name": "wiredTiger",

  "supportsCommittedReads": true,

  "persistent": true

}