Databases & data
Development, infrastructure, SEO, AI and IT for business — short and to the point.
70 articles
- Databases & data4 min
Database Transactions and ACID Explained Simply
A transaction groups several database operations into one all-or-nothing unit; ACID means it either fully happens or not at all (atomicity), keeps data valid (consistency), does not get confused by parallel transactions (isolation) and survives a crash once committed (durability).
Basics - Databases & data4 min
Change Data Capture (CDC) with Debezium Explained
Log-based CDC reads the database transaction log and turns every insert, update and delete into an event; Debezium does this for PostgreSQL, MySQL and others and publishes the events to Kafka, keeping warehouses, search indexes and caches in sync within seconds instead of after the next batch job.
Advanced - Databases & data4 min
Data Cleaning: How to Prepare Data for Analysis
Data cleaning is a sequence of steps: find and remove duplicates, decide how to treat missing values, bring formats to one standard, flag outliers and document every rule so the process can be repeated.
Practice - Databases & data4 min
Data Lake vs Data Warehouse vs Lakehouse
A data warehouse stores cleaned, structured data for reporting, a data lake stores any raw data cheaply in its original form, and a lakehouse adds warehouse-style tables and transactions on top of a lake. Many small companies only need a regular database and a BI tool.
Basics - Databases & data4 min
Database Deadlocks: Why They Happen and How to Fix Them
A deadlock happens when two transactions each hold a lock the other needs, so the database kills one of them; you fix it by acquiring locks in the same order everywhere, keeping transactions short, and retrying the transaction that was rolled back.
Advanced - Databases & data4 min
Common Database Design Mistakes and How to Avoid Them
Most data problems start in the schema: keep one value per cell, enforce constraints in the database, use numeric for money, consistent names, timestamps and timestamptz for time.
Practice - Databases & data4 min
Database Indexes Explained: How They Speed Up Queries
An index is a separate sorted structure, usually a B-tree, that lets the database jump straight to matching rows instead of reading the whole table; it speeds up reads but slows down every insert, update and delete, so add indexes for real queries, not just in case.
Basics - Databases & data4 min
Database Migrations: How to Change Schema Safely
Change the schema only through numbered migrations in your repository, apply them automatically on deploy, and split risky changes into compatible steps so old and new code can both work with the database.
Practice - Databases & data5 min
Database Normalization: 1NF, 2NF, 3NF with Examples
Normalization means splitting data into tables so that every fact is stored once: 1NF removes lists inside cells, 2NF removes columns that depend on only part of a composite key, 3NF removes columns that depend on other non-key columns; denormalize only deliberately, for measured read performance or reporting.
Basics - Databases & data4 min
How to Add Full-Text Search to a Site with Elasticsearch
Create an index with separate fields per language and proper analyzers, keep it in sync with your main database through events or periodic reindexing, and use fuzziness plus search_as_you_type for typos and autocomplete.
Practice - Databases & data4 min
Elasticsearch Analyzers for Russian and Uzbek Search
Index each product name twice — once with a Russian analyzer (stemming, synonyms) and once through a Cyrillic-to-Latin transliteration analyzer — then query both with fuzziness so that “non”, “нон” and “nonn” all find bread.
Practice - Databases & data3 min
ETL vs ELT: How Data Pipelines Work
ETL transforms data first and then loads it into the warehouse, while ELT loads raw data first and transforms it inside the warehouse. Cloud warehouses usually favor ELT because their compute is cheap to scale.
Basics - Databases & data4 min
The N+1 Query Problem: How to Detect and Fix It
N+1 happens when code runs one query for a list and then one more query per item; you fix it by loading related data up front in one or two queries with eager loading, JOINs or batching.
Practice - Databases & data4 min
How to Choose a Database for Your Project
For most projects start with PostgreSQL as the main database and add Redis, a search engine or a document store only when a specific, measured need appears.
Practice - Databases & data4 min
How to Import CSV and Excel Data into PostgreSQL
Load the file into a staging table with text columns first using COPY, \copy, DBeaver or Python, then cast types, remove duplicates and move only validated rows into the real table.
Practice - Databases & data4 min
How to Install and Configure PostgreSQL on Ubuntu
Install PostgreSQL from the Ubuntu repositories with apt, create a separate login role and database for your app, open remote access only for specific IP addresses via listen_addresses and pg_hba.conf, and size shared_buffers, work_mem and connections to your VPS memory.
Practice - Databases & data4 min
How to Build a KPI Dashboard for a Business
Start from the decisions the dashboard must support, pick a few KPIs per department, combine CRM, 1C and spreadsheet data in one store with shared reference data, then build a summary-trends-details layout with a clear refresh schedule.
Practice - Databases & data5 min
Designing a Ledger Database for Payments and Balances
Store every money movement as an immutable transaction with entries that sum to zero, keep amounts as integers in tiyin, make provider callbacks idempotent with a unique key, and lock the account row before debiting it.
Advanced - Databases & data4 min
Looker Studio Guide: Free Dashboards from Google Sheets
Looker Studio turns Google Sheets, BigQuery and dozens of other sources into interactive dashboards for free. What matters most is a clean source table and deliberate sharing settings: whose credentials the data source uses and who can download the data.
Practice - Databases & data4 min
How to Set Up Metabase for Business Dashboards
Run Metabase in Docker with its own PostgreSQL application database, connect your data through a read-only user, build questions into dashboards, restrict access with groups and send dashboards by email on a schedule.
Practice - Databases & data4 min
How to Migrate from MySQL to PostgreSQL
Migrating from MySQL to PostgreSQL is more than copying data: first audit types and application queries, then move the data with pgloader to a test environment, validate it, and only after a rehearsal switch the app over in a short window with a rollback plan.
Practice - Databases & data4 min
MongoDB Aggregation Pipeline: $match, $group, $lookup Explained
An aggregation pipeline is a chain of stages where each one processes the output of the previous; filter with $match as early as possible, aggregate with $group, and run $lookup only on a small result set.
Practice - Databases & data4 min
MongoDB Schema Design: Embedding vs Referencing
Embed data that is read together and bounded in size, reference data that is shared, large or grows without limit, and design the schema around your most frequent queries.
Practice - Databases & data4 min
How to Back Up and Restore a MySQL Database
For most databases, mysqldump with --single-transaction, run on a schedule and copied to another location, is enough; for large databases and fast restores, use Percona XtraBackup.
Practice - Databases & data3 min
OLTP vs OLAP: Transactional vs Analytical Databases
OLTP databases handle many small application operations such as orders, payments and sign-ups. OLAP databases are built for heavy analytical queries over large amounts of history. Mixing both workloads in one database is a common cause of slow production systems.
Basics - Databases & data4 min
Connection Pooling with PgBouncer: Setup and Pitfalls
PgBouncer lets thousands of clients share a small number of real PostgreSQL connections; use transaction mode for most web and serverless apps, but avoid session-level state and handle prepared statements explicitly.
Advanced - Databases & data4 min
PostgreSQL Backup and Restore with pg_dump and pg_restore
Use pg_dump in the custom format (-Fc) for compressed, flexible backups and restore them with pg_restore; save roles separately with pg_dumpall --globals-only. Automate dumps with cron, keep several copies including one off the server, and regularly test that a restore actually works.
Practice - Databases & data4 min
How to Find Slow Queries in PostgreSQL with EXPLAIN ANALYZE
First find the most expensive queries with pg_stat_statements or log_min_duration_statement, then run EXPLAIN (ANALYZE, BUFFERS) on them and look for the node where time is spent, usually a Seq Scan on a large table or an extra sort that the right index fixes.
Practice - Databases & data4 min
PostgreSQL Full-Text Search: Do You Need Elasticsearch
For most sites PostgreSQL is enough: tsvector with a GIN index gives relevant word search and pg_trgm handles typos, while Elasticsearch pays off only with heavy search load, complex ranking or rich faceted search.
Practice - Databases & data4 min
PostgreSQL Index Types: B-tree, GIN, GiST, BRIN and When to Use Them
B-tree covers equality, ranges and sorting; GIN covers “contains” searches in jsonb, arrays and full text; GiST covers overlaps, geometry and nearest-neighbour; BRIN covers huge append-only tables ordered by time.
Advanced - Databases & data4 min
PostgreSQL JSONB: When and How to Store JSON in a Table
Store JSON in a jsonb column, index it with GIN and use it for truly flexible data such as product attributes and raw webhooks; anything you filter on, join on or count money with belongs in regular columns.
Practice - Databases & data4 min
PostgreSQL Point-in-Time Recovery with WAL Archiving
Point-in-time recovery restores a base backup and then replays archived WAL files up to a chosen moment, so you can return the database to the second before a bad DELETE; it requires continuous WAL archiving and regular restore tests.
Advanced - Databases & data4 min
PostgreSQL Users, Roles and Permissions Done Right
A sound PostgreSQL permission model uses group roles without login (owner, application, analytics) and separate login roles that are members of them; privileges come from GRANT and ALTER DEFAULT PRIVILEGES, BI gets read-only access, and Row-Level Security isolates rows.
Practice - Databases & data4 min
How to Set Up PostgreSQL Streaming Replication
Allow replication on the primary, create a role and a slot, build the standby with pg_basebackup -R, watch lag in pg_stat_replication, and fail over with pg_promote or automatically with Patroni.
Advanced - Databases & data4 min
PostgreSQL vs MySQL: Which Database to Choose
Both databases are reliable and fit most projects. PostgreSQL is the richer choice for complex logic, reporting, JSON and geodata; MySQL is the simple, widely available option for typical websites, CMSs like WordPress and workloads of simple queries.
Basics - Databases & data4 min
Power BI for Beginners: Build Your First Report
Your first Power BI report takes five steps: connect the sources, clean the data in Power Query, link tables into a star schema, write a few DAX measures and publish to the Power BI Service with scheduled refresh.
Practice - Databases & data4 min
Power BI vs Metabase vs Looker Studio: Which BI Tool to Pick
Looker Studio is the fast free start for teams on Google Sheets and Google services; Metabase is the best fit when data lives in your own SQL database and someone can run a server; Power BI is for complex analytics and companies in the Microsoft ecosystem.
Practice - Databases & data4 min
Primary Key vs Foreign Key: Relationships in Databases
A primary key uniquely identifies each row in its own table, while a foreign key is a column that points to a primary key in another table; together they build relationships between tables and let the database block links to rows that do not exist.
Basics - Databases & data4 min
How to Build a Simple ETL Pipeline in Python
A simple Python ETL is three functions (extract, transform, load) plus four reliability rules: retries on network failures, idempotent loading via upsert, incremental extraction by timestamp, and scheduled runs with logs.
Practice - Databases & data4 min
Redis Persistence: RDB vs AOF and How Not to Lose Data
RDB takes periodic snapshots and can lose changes since the last one, while AOF logs every write and with appendfsync everysec usually loses no more than a second; for sessions and queues enable AOF alongside RDB, for a pure cache persistence is often unnecessary.
Practice - Databases & data3 min
Redis Use Cases: Caching, Sessions, Queues and Rate Limits
Redis is an in-memory store for fast, short-lived data: use it for cache with TTL, sessions, lightweight queues, pub/sub, leaderboards and rate limits, while keeping the source of truth in your main database.
Practice - Databases & data4 min
Database Sharding vs Partitioning: Scaling Large Tables
Partitioning divides one large table into smaller pieces inside a single database server, while sharding spreads data across several servers by a shard key; start with partitioning and shard only when one server truly cannot cope.
Advanced - Databases & data4 min
SQL Basics: SELECT, WHERE, ORDER BY and LIMIT
Almost every read query follows the pattern SELECT columns FROM table WHERE condition ORDER BY sorting LIMIT count. Learn these five parts plus LIKE, IN and IS NULL, and you can pull most of the data you need from a database.
Basics - Databases & data3 min
SQL GROUP BY, HAVING and Aggregate Functions
GROUP BY collects rows into groups, aggregate functions compute one value per group, WHERE filters rows before grouping and HAVING filters the finished groups.
Practice - Databases & data4 min
SQL INSERT, UPDATE and DELETE: How to Change Data Safely
INSERT adds rows, UPDATE changes them and DELETE removes them; to change data safely, preview the WHERE clause with SELECT, run the change inside a transaction and check the affected row count before COMMIT.
Basics - Databases & data5 min
SQL JOINs Explained: INNER, LEFT, RIGHT and FULL
A JOIN combines rows from two tables by a matching condition: INNER keeps only matches, LEFT keeps every row of the left table, RIGHT keeps every row of the right table, and FULL keeps everything from both, filling the gaps with NULL.
Basics - Databases & data4 min
NULL in SQL: IS NULL, COALESCE and Common Traps
NULL means an unknown value, so any comparison with it gives UNKNOWN instead of true or false; check it with IS NULL, replace it with COALESCE, and forbid it with NOT NULL wherever a value must always exist.
Basics - Databases & data4 min
SQL Pagination: OFFSET vs Keyset (Cursor) Pagination
OFFSET forces the database to read and discard every skipped row and drifts when rows are inserted; keyset pagination continues from the last shown record with a WHERE on a stable sort and stays equally fast at any depth.
Practice - Databases & data4 min
SQL Query Optimization Checklist
Measure the query with EXPLAIN ANALYZE first, then select only the columns you need, write filters that can use an index, replace OFFSET with keyset pagination and remove N+1 with batched queries.
Practice - Databases & data4 min
SQL Subqueries vs CTE: How to Write Readable Queries
A subquery suits a short check inside a condition, a CTE (WITH) suits multi-step logic you want to read top to bottom, and a recursive CTE is the standard way to walk a hierarchy; in modern databases their speed is usually the same.
Practice - Databases & data4 min
SQL vs NoSQL: Differences and When to Use Each
SQL databases store data in related tables with a strict schema and reliable transactions, while NoSQL stores documents, key-value pairs, columns or graphs with a more flexible structure. Most business apps should start with SQL and add NoSQL for a specific job.
Basics - Databases & data4 min
SQL Window Functions: ROW_NUMBER, RANK, LAG and More
A window function computes a value over a set of related rows but, unlike GROUP BY, does not collapse them: every row stays in the result and gets a number, rank, running sum or a neighboring row's value.
Practice - Databases & data4 min
Star Schema vs Snowflake Schema: Data Modeling for Analytics
Both schemas put measurable events in a central fact table surrounded by dimensions; a star keeps each dimension in one wide table for simple, fast queries, while a snowflake splits dimensions into normalized sub-tables, and most BI tools work best with a star.
Basics - Databases & data4 min
Transaction Isolation Levels: Dirty Reads to Serializable
Isolation levels define which anomalies concurrent transactions can see: Read Committed blocks dirty reads, Repeatable Read also blocks non-repeatable reads, and Serializable behaves as if transactions ran one by one; for read-modify-write logic use SELECT FOR UPDATE or an atomic UPDATE.
Advanced - Databases & data4 min
Data Analytics Basics: Descriptive, Diagnostic, Predictive
Analytics answers four questions in order: what happened (descriptive), why it happened (diagnostic), what will happen (predictive) and what to do about it (prescriptive). Every useful analysis starts with a clear business question and a precisely defined metric, not with the data.
Basics - Databases & data4 min
UUID vs Auto-Increment ID: Choosing a Primary Key
For a typical web or mobile backend a sensible default is UUIDv7 in a native uuid column: it can be generated anywhere, does not reveal volumes and inserts almost like auto-increment; bigint identity is great for internal tables in a single database.
Practice - Databases & data4 min
What Is a Data Warehouse and Why Businesses Need One
A data warehouse (DWH) is a separate database for analytics that regularly pulls in data from your CRM, accounting, website and ads, so every business question is answered from the same verified numbers.
Basics - Databases & data4 min
What Is a Database and How Does It Work
A database is an organized store of information, and a DBMS is the software that saves it to disk, finds what you ask for quickly and keeps the data consistent when many users work with it at once.
Basics - Databases & data4 min
What Is a Graph Database and When to Use Neo4j
A graph database stores data as nodes and the relationships between them and walks chains of relationships of any depth quickly; use it when the core question is who is connected to whom and through what, not how much.
Basics - Databases & data4 min
What Is a Time-Series Database: TimescaleDB, InfluxDB and More
A time-series database is optimized for data that arrives as timestamped measurements, is mostly appended, queried by time ranges and aged out over time; start with PostgreSQL, and move to TimescaleDB, InfluxDB, ClickHouse or Prometheus when volume, retention or rollups make plain tables painful.
Basics - Databases & data3 min
What Is an ORM: Pros, Cons and Popular Examples
An ORM is a library that lets you work with database tables as objects in code and generates the SQL for you. It speeds up routine development, but you still need to know which queries hit the database, or you will run into the N+1 problem and slow pages.
Basics - Databases & data3 min
What Is Business Intelligence (BI) and How It Helps Decisions
Business Intelligence (BI) is a set of tools and processes that turns data from operational systems into regular reports and dashboards, so decisions rely on current numbers instead of gut feeling.
Basics - Databases & data3 min
What Is ClickHouse and Why Analytics Teams Use It
ClickHouse is an open-source columnar database designed for analytics: it scans and aggregates billions of rows quickly because it reads only the needed columns and compresses them well. It is a poor fit for frequent single-row updates and transactions, so it usually works next to PostgreSQL, not instead of it.
Basics - Databases & data4 min
What Is Database Replication and Why It Matters
Replication continuously copies changes from a primary database to one or more replicas, so you can spread read load and switch to a replica if the primary fails. It protects against server failure, not against mistakes: a deleted table is deleted on every replica too, so you still need backups.
Basics - Databases & data4 min
What Is dbt and How It Transforms Data in the Warehouse
dbt is a tool that runs data transformations directly in your warehouse: you write models as plain SELECT queries, and dbt builds them in the right order, tests them and documents them.
Basics - Databases & data4 min
What Is Elasticsearch and How Search Engines Index Data
Elasticsearch is a distributed search engine that stores JSON documents in an inverted index, so it finds matching words across millions of records fast and ranks results by relevance; you need it when database LIKE queries can no longer deliver good full-text search.
Basics - Databases & data4 min
What Is MongoDB and When Should You Use It
MongoDB is a document NoSQL database that stores data as JSON-like documents in collections without a rigid schema. It is handy for flexible and nested data, while linked financial and accounting data is usually safer in a relational database.
Basics - Databases & data4 min
What Is Redis and Why Is It So Fast
Redis is a key-value store that keeps all data in RAM, which is why it responds so quickly. It is used for caching, sessions, queues, counters and leaderboards rather than as the only database for important data.
Basics - Databases & data4 min
What Is SQLite and When Is It Enough
SQLite is a full SQL database packed into a library that keeps everything in a single file, with no separate server. It is enough while one machine accesses the data and writes are moderate; when many processes or servers need to write at once, move to PostgreSQL or MySQL.
Basics - Databases & data4 min
Zero-Downtime Database Schema Changes: Expand and Contract
Never change a live schema in one breaking step: first expand (add new structures that work alongside the old ones), migrate data and code gradually, then contract (remove the old parts) once nothing uses them.
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