Database on Nalar

Transaction Isolation and Safe Database Retries

Tue, 01 Sep 2026 00:00:00 +0700

Database transactions make groups of reads and writes atomic, but atomicity alone does not answer what concurrent transactions are allowed to observe. That is the job of isolation.

The practical challenge appears when correct transactions conflict. Strong isolation can intentionally abort one transaction rather than allow an invalid interleaving. Applications need to distinguish those retryable concurrency failures from ordinary errors.

Isolation protects invariants, not just statements

Consider two concurrent requests that reserve the last available item.

Configuring Remote MySQL Access on Linux

Thu, 29 Sep 2022 00:00:00 +0700

MySQL installations are commonly configured to listen only on a local interface. If a database must accept connections from another machine, you need to adjust the server’s listening address, create an appropriately scoped account, and make sure the network firewall allows only the required clients.

Step 1: Update the MySQL Configuration

Edit the MySQL configuration file

On Ubuntu and Debian installations, a common file is:
$el.innerText = 'Copy', 2000)" class="absolute top-2 right-2 bg-neutral-700 text-white text-xs px-2 py-1 rounded opacity-0 group-hover:opacity-100 transition-opacity" > Copy
```
sudo nano /etc/mysql/mysql.conf.d/mysqld.cnf
```
Change bind-address

Exporting and Restoring MongoDB Databases with `mongodump` and `mongorestore`

Wed, 06 Oct 2021 00:00:00 +0700

Backups are an important part of MongoDB administration. Two standard command-line tools for logical backups and restores are mongodump and mongorestore, which work with BSON data and collection metadata.

1. Back Up a Database with `mongodump`

Use mongodump to create a BSON backup that can later be restored.

Basic syntax:

$el.innerText = 'Copy', 2000)" class="absolute top-2 right-2 bg-neutral-700 text-white text-xs px-2 py-1 rounded opacity-0 group-hover:opacity-100 transition-opacity" > Copy

mongodump -d <database_name> -o <backup_directory>

-d <database_name> → the database to back up.
-o <backup_directory> → the directory where the dump will be written.

Example:

Using MongoDB Aggregation to Build Hierarchical Category Structures

Tue, 05 Oct 2021 00:00:00 +0700

Applications often need to represent hierarchical data such as parent categories, child categories, and deeper descendants. MongoDB’s aggregation framework includes $graphLookup, which can recursively traverse relationships within a collection.

This article shows how to use $graphLookup to retrieve a category hierarchy from documents that reference their parent category.

1. Data Structure

Consider the following documents in a MongoDB collection:

$el.innerText = 'Copy', 2000)" class="absolute top-2 right-2 bg-neutral-700 text-white text-xs px-2 py-1 rounded opacity-0 group-hover:opacity-100 transition-opacity" > Copy

{ "_id" : 1, "cat_id" : 1, "title" : "Parent Category", "parent" : null }
{ "_id" : 2, "cat_id" : 2, "title" : "Child Category", "parent" : 1 }
{ "_id" : 3, "cat_id" : 3, "title" : "Sub Child Category", "parent" : 2 }

The relationships are:

How to Create Users and Databases in MySQL

Wed, 08 Sep 2021 00:00:00 +0700

Managing users and databases is a fundamental MySQL administration task. This guide shows how to create a user, create a database, and grant that user the permissions needed to work with the database.

1. Create a New MySQL User

Start by creating a user with its own login credentials.

Basic syntax:

$el.innerText = 'Copy', 2000)" class="absolute top-2 right-2 bg-neutral-700 text-white text-xs px-2 py-1 rounded opacity-0 group-hover:opacity-100 transition-opacity" > Copy

CREATE USER 'user' IDENTIFIED BY 'password';

'user': the username to create.
'password': the password for that user.

Example:

Database on Nalar

Transaction Isolation and Safe Database Retries

Isolation protects invariants, not just statements

Configuring Remote MySQL Access on Linux

Step 1: Update the MySQL Configuration

Exporting and Restoring MongoDB Databases with `mongodump` and `mongorestore`

1. Back Up a Database with mongodump

Using MongoDB Aggregation to Build Hierarchical Category Structures

1. Data Structure

How to Create Users and Databases in MySQL

1. Create a New MySQL User

1. Back Up a Database with `mongodump`