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Scaling Databases Horizontally: A Solution for High-Concurrency Systems
By Sukan   |   September 20, 2023   |   Posted in : TiDB
Blog post on how TiDB handles the OLAP requests without compromising OLTP

6 Interesting Features In MongoDB 6.0
By Thivakar   |   June 19, 2023   |   Posted in : MongoDB
Upgrade to MongoDB 6.0 for improved index management, error handling, powerful aggregation, replicaset enhancements, time series collection improvements, and embedded field exclusion. Experience efficient database management.

Access Control & Account Management In MySQL 8
By Sukan   |   June 08, 2023   |   Posted in : MySQL
Discover how MySQL 8 enhances security through features like password expiry, password validation, account lock/unlock, privilege management, and dual passwords. Safeguard your valuable data and streamline access control in your MySQL environment.

Significance of using Invisible Primary key (GIPK) with MySQL 8.0
By Sukan   |   February 21, 2023   |   Posted in : MySQL
How Generated Invisible Primary Keys (GIPK) Can Boost Your Database Efficiency

Achieving High Availability Using Log Shipping
By Sujith   |   February 21, 2018   |   Posted in : SQL Server
Here we will get the detailed explanation of how we can achieve HA using Log Shipping.

 Home  /  Mongodb  
Insight on MongoDB Transactions
By AKumar   |   July 10, 2019   |   Posted in : Mongodb

Before version 4.0, MongoDB uses $isolated operator to update multiple documents but it does not provide “all-or-nothing” atomicity for write operations.

MongoDB resolved this issue in version 4.0 and provides the support of Multi-Document transactions. 
Prior to starting a transaction, a session must be created. A transaction cannot be run outside a session.

At any given time you may have multiple running sessions in the system, but each session may run only a single transaction at a time. You can run transactions in parallel according to how many open sessions you have.

The following mongo shell methods are available for Transactions to Start & Commit or Abort :

How it works?

Below example clearly explains how transactions work in MongoDB. Here we will be implementing transactions by creating two different sessions.

Session 1 :

In this session 1, I am starting a transaction and inserting a document without commiting the transaction.

Session 2 :

Lets find the inserted document.

Before Commiting the transaction: No result set, as Session 1 did not commit the transaction.

Session 1:

Now again in the session 1, lets commit the transaction.

Session 2 :

Now, when we find the document, we could see the same data that we have inserted already in session1.

Note : By default, trananaction uses Read Commited isolation and we can't change the isolation level. 

Limitations of Transactions :
  1. A collection cannot be dropped or created inside a transaction.

  2. It is not possible to read and write into a system.* collection.

  3. An index cannot be created or dropped inside a transaction.

  4. We can’t use transactions on a standalone server, we need to configure it as a replica set.

  5. By default, a transaction that executes for longer than 60 seconds will automatically expire.

  6. A transaction cannot read or write in config, admin, and local databases.

  7. Size of a transaction is limited to 16MB.

Note: From upcoming MongoDB version(4.2), transaction will get supported in shared cluster as well.


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