When can an ultra-fast query be considered bad?

In the world of databases, the quest for ultra-fast queries is almost a mantra. DBAs, DevOps, and Tech Leads go to great lengths to optimize every millisecond of response, believing that speed is the only indicator of success. But what if I told you that a query, despite seeming fast, can be a sneaky parasite, sucking the life out of your database and putting your entire infrastructure at risk? Yes, you read that right. A fast execution is not always synonymous with health or efficiency. In fact, it can be the Trojan horse that compromises the performance, availability, and security of your data.

This article from HTI Tecnologia, your partner in database management and optimization, will unveil the mysteries behind “fast and bad queries.” Prepare to question your assumptions and learn how to identify these hidden villains before they cause irreparable damage. If you are an Infrastructure Manager or an IT/CTO Manager, understanding these signs is crucial to protecting the heart of your operation.

The Illusion of Speed: Why Can a Fast Query Be Bad?

Imagine a runner who sprints at the start of a marathon but expends all their energy in the first few meters, compromising the rest of the race. This is exactly what happens with many queries. They can return results quickly to the end-user, giving a false sense of efficiency. However, behind the scenes, this apparent speed can come at a high cost: consuming excessive server resources, blocking other critical operations, causing inconsistencies, or even exposing security vulnerabilities.

HTI Tecnologia has vast experience in diagnosing and solving these complex problems for medium and large-sized companies. Our specialists know that a database’s performance is not just measured by the speed of an isolated query but by the systemic impact it creates.

1. Excessive Resource Consumption: The Silent Vampire of Your Infrastructure

A query can be fast because it “steals” resources from other operations. This means that while it executes quickly, it’s overloading the CPU, RAM, or disk I/O of your server. The result? Other applications and services that depend on the same database begin to experience slowness, timeouts, and eventually, failures. The overall system performance plummets.

Warning Sign: Monitor your server’s resource usage. If a specific query always coincides with CPU or I/O peaks, even if it returns in a few milliseconds, something is wrong.

How HTI Tecnologia Helps: Our 24/7 consulting and support services include proactive monitoring and in-depth performance analysis. We identify these “vampire” queries and apply optimizations that balance resource usage, ensuring the stability of your entire environment.

SELECT TOP 10
    qs.total_worker_time / 1000 AS total_cpu_time_ms,
    qs.total_elapsed_time / 1000 AS total_elapsed_time_ms,
    qs.total_logical_reads AS total_reads,
    qs.total_logical_writes AS total_writes,
    qs.execution_count,
    SUBSTRING(st.text, (qs.statement_start_offset / 2) + 1,
        ((CASE qs.statement_end_offset
            WHEN -1 THEN DATALENGTH(st.text)
            ELSE qs.statement_end_offset
        END - qs.statement_start_offset) / 2) + 1) AS statement_text
FROM
    sys.dm_exec_query_stats AS qs
CROSS APPLY
    sys.dm_exec_sql_text(qs.sql_handle) AS st
ORDER BY
    qs.total_worker_time DESC;

// MongoDB: Identifying active operations with high execution time or blocks
db.currentOp({
    "active": true,
    "secs_running": { "$gt": 5 } // Operations running for more than 5 seconds
})

// Or to see operations that are waiting for locks
db.currentOp({
    "active": true,
    "waitingForLock": true
})

2. Blocks and Deadlocks: Paralyzing Your Database

A query that seems fast in your test environment or during low traffic can become a blocking monster in production. Poorly designed queries, especially those that involve updates on large volumes of data without the proper locking strategy, can hold important resources, preventing other transactions from completing. The worst-case scenario is a deadlock, where two or more transactions are mutually waiting for each other to release resources, paralyzing the system.

Warning Sign: Users complaining about intermittent slowness, transactions that never finish, or deadlock errors in the database logs.

HTI’s Expertise: Our specialized DBAs in SQL and NoSQL (MySQL, MariaDB, PostgreSQL, Oracle, SQL Server, MongoDB, Redis, Neo4J) are masters at identifying and resolving blocking and deadlock issues, optimizing transactions and ensuring operational continuity.

SELECT
    pg_blocking_pids(pid) AS blocked_by,
    pid AS blocked_pid,
    usename AS blocked_user,
    query AS blocked_query
FROM
    pg_stat_activity
WHERE
    pg_blocking_pids(pid) IS NOT NULL;

SELECT
    p.id AS processid,
    p.user,
    p.host,
    p.db,
    p.command,
    p.time,
    p.state,
    p.info,
    l.lock_mode
FROM
    information_schema.processlist p
JOIN
    performance_schema.data_locks l ON p.id = l.thread_id
WHERE
    l.lock_status = 'WAIT';

BEGIN TRAN;
UPDATE Produtos SET Estoque = Estoque - 1 WHERE Id = 1;

UPDATE Pedidos SET Status = 'Processando' WHERE ProdutoId = 2;
COMMIT TRAN;


BEGIN TRAN;
UPDATE Pedidos SET Status = 'Processando' WHERE ProdutoId = 2;

UPDATE Produtos SET Estoque = Estoque - 1 WHERE Id = 1;
COMMIT TRAN;

3. Lack of Scalability: The Achilles’ Heel of Growth

A fast query today can be slow tomorrow. If it was optimized for a small volume of data and does not account for future growth, it will become a bottleneck as your database expands. What was once a quick execution now drags on for minutes, hours, or even crashes the system during peak demand.

Warning Sign: System performance degrades proportionally to the increase in data volume or number of users, even with few code changes.

HTI’s Solutions: HTI Tecnologia designs and implements robust scalability strategies, reviewing the design of your queries and database schemas to ensure they support your business growth without compromising performance.

SELECT *
FROM Pedidos
WHERE DataPedido BETWEEN '2023-01-01' AND '2023-01-31'
AND ValorTotal > 1000
ORDER BY DataPedido DESC;

EXPLAIN ANALYZE
SELECT *
FROM Pedidos
WHERE DataPedido BETWEEN '2023-01-01' AND '2023-01-31'
AND ValorTotal > 1000
ORDER BY DataPedido DESC;

CREATE INDEX ix_pedidos_data_valor ON Pedidos (DataPedido, ValorTotal);

// MongoDB: Example of a query that may not scale without an index on a large collection
// 'logs' collection with millions of documents, 'timestamp' and 'level' not indexed.
db.logs.find({
    "timestamp": { "$gte": ISODate("2023-01-01T00:00:00Z"), "$lt": ISODate("2023-01-02T00:00:00Z") },
    "level": "ERROR"
}).sort({ "timestamp": -1 }).limit(10).explain("executionStats");

// Optimization: Create a compound index
db.logs.createIndex({ "timestamp": 1, "level": 1 });

4. Data Inconsistency: The Price of Careless Speed

In some cases, to achieve apparent speed, a query may be accessing outdated, incomplete, or even incorrect data. This can happen, for example, with the improper use of hints, outdated indexes, or flawed business logic that prioritizes fast reads over transactional integrity. Inconsistent data is a recipe for disaster, especially in critical financial or inventory systems.

Warning Sign: Discrepant reports, data that doesn’t match between different systems, or user complaints about incorrect information.

The HTI Vision: We prioritize data security and integrity above all else. Our specialists audit your queries and procedures to ensure that speed does not compromise the reliability of your information.

SELECT
    ProdutoId,
    NomeProduto,
    Estoque
FROM
    Produtos WITH (NOLOCK) -- AVOID USING NOLOCK WITHOUT UNDERSTANDING THE RISKS!
WHERE
    Estoque < 10;

UPDATE ContaCorrente SET Saldo = Saldo - 100 WHERE Id = 1;
UPDATE HistoricoTransacoes SET Tipo = 'Débito', Valor = 100 WHERE ContaId = 1;

BEGIN TRANSACTION;
UPDATE ContaCorrente SET Saldo = Saldo - 100 WHERE Id = 1;

IF @@ERROR <> 0
BEGIN
    ROLLBACK TRANSACTION;
    
END;
UPDATE HistoricoTransacoes SET Tipo = 'Débito', Valor = 100 WHERE ContaId = 1;
IF @@ERROR <> 0
BEGIN
    ROLLBACK TRANSACTION;
    
END;
COMMIT TRANSACTION;

5. Hidden Queries and Background Impact: The Domino Effect

The problem isn’t always with the query you see. Often, a “fast” query triggers other operations in the background – triggers, stored procedures, index updates, logs – that, combined, generate a significant systemic impact. The execution time of the main query may be low, but the total cost of the operation is high.

Warning Sign: Inexplicably low database performance, even when “main” queries seem fast, and system logs are full of secondary operations.

How We Unveil: HTI Tecnologia uses advanced profiling and tracing tools to map the complete execution flow of your operations, identifying side effects and optimizing the entire process.

CREATE TABLE LogsAuditoria (
    IdLog SERIAL PRIMARY KEY,
    TabelaAlterada VARCHAR(100),
    Acao VARCHAR(50),
    Usuario VARCHAR(100),
    DataHora TIMESTAMP DEFAULT NOW()
);

CREATE OR REPLACE FUNCTION log_produtos_alteracoes()
RETURNS TRIGGER AS $$
BEGIN
    INSERT INTO LogsAuditoria (TabelaAlterada, Acao, Usuario)
    VALUES ('Produtos', 'UPDATE', CURRENT_USER);
    RETURN NEW;
END;
$$ LANGUAGE plpgsql;

CREATE TRIGGER trg_log_produtos_update
AFTER UPDATE ON Produtos
FOR EACH ROW
EXECUTE FUNCTION log_produtos_alteracoes();

UPDATE Produtos SET Preco = Preco * 1.05 WHERE Categoria = 'Eletronicos';

6. Excessive Complexity and Maintenance Difficulty: A Future Time Bomb

A query can be “fast” by using tricks or overly complex solutions that, while they work in the short term, are impossible for other DBAs or developers to maintain or understand. When the data volume increases or the system needs a new feature, this complexity becomes a nightmare, leading to bugs, rework, and delays.

Warning Sign: Difficulty debugging queries, long periods to implement small changes, or the need for “guru DBAs” to understand the existing code.

The HTI Standard: We promote best practices for query development and maintenance, ensuring that the code is efficient, readable, and scalable, avoiding future headaches.

SELECT
    p.NomeProduto,
    (SELECT AVG(op.Quantidade * op.PrecoUnitario) FROM DetalhesPedido op WHERE op.ProdutoId = p.Id) AS MediaVendaProduto,
    (SELECT COUNT(DISTINCT c.Id) FROM Clientes c JOIN Pedidos pd ON c.Id = pd.ClienteId JOIN DetalhesPedido dp ON pd.Id = dp.PedidoId WHERE dp.ProdutoId = p.Id AND pd.DataPedido BETWEEN DATEADD(month, -6, GETDATE()) AND GETDATE()) AS ClientesNosUltimos6Meses
FROM
    Produtos p
WHERE
    p.Id IN (
        SELECT DISTINCT dp.ProdutoId
        FROM DetalhesPedido dp
        JOIN Pedidos pe ON dp.PedidoId = pe.Id
        WHERE pe.ValorTotal > 500
    )
ORDER BY
    p.NomeProduto;

WITH ProdutosVendidos AS (
    SELECT
        dp.ProdutoId,
        SUM(dp.Quantidade * dp.PrecoUnitario) AS TotalVendido,
        COUNT(DISTINCT pe.ClienteId) AS TotalClientes
    FROM
        DetalhesPedido dp
    JOIN
        Pedidos pe ON dp.PedidoId = pe.Id
    WHERE
        pe.DataPedido BETWEEN DATEADD(month, -6, GETDATE()) AND GETDATE()
    GROUP BY
        dp.ProdutoId
)
SELECT
    p.NomeProduto,
    AVG(dp.Quantidade * dp.PrecoUnitario) AS MediaVendaProduto,
    pv.TotalClientes AS ClientesNosUltimos6Meses
FROM
    Produtos p
LEFT JOIN
    DetalhesPedido dp ON p.Id = dp.ProdutoId
LEFT JOIN
    ProdutosVendidos pv ON p.Id = pv.ProdutoId
GROUP BY
    p.Id, p.NomeProduto, pv.TotalClientes
HAVING
    SUM(dp.Quantidade * dp.PrecoUnitario) > 500 
ORDER BY
    p.NomeProduto;

7. Security Vulnerabilities: The Open Door to Attacks

A fast query can be the result of a design that ignores basic security principles. For example, queries with direct string concatenation instead of parameterized parameters (SQL Injection) can be very fast to execute but open a critical breach for attacks. Similarly, queries that return unnecessary or sensitive data to the client can compromise the confidentiality of the information.

Warning Sign: Lack of input sanitization, the use of excessive permissions for application users, or sensitive data exposed in logs or interfaces.

Security is Essential: At HTI Tecnologia, security is a fundamental pillar of all our services. Our specialists perform security audits and ensure that your queries and your database design are protected against the latest threats.

DECLARE @NomeUsuario VARCHAR(50) = 'admin'; 
DECLARE @Senha VARCHAR(50) = 'password';   

SET @Senha = ''' OR ''1''=''1 --';

DECLARE @SQL NVARCHAR(MAX);
SET @SQL = 'SELECT * FROM Usuarios WHERE NomeUsuario = ''' + @NomeUsuario + ''' AND Senha = ''' + @Senha + '''';

PRINT @SQL;

DECLARE @NomeUsuarioSeguro NVARCHAR(50) = 'admin';
DECLARE @SenhaSegura NVARCHAR(50) = 'password';

EXEC sp_executesql
    N'SELECT * FROM Usuarios WHERE NomeUsuario = @UserParam AND Senha = @PassParam',
    N'@UserParam NVARCHAR(50), @PassParam NVARCHAR(50)',
    @UserParam = @NomeUsuarioSeguro,
    @PassParam = @SenhaSegura;

// MongoDB: Example of a secure query (MongoDB uses BSON for inputs, preventing injection by default)
// Still, it's important to validate and sanitize inputs.
// Vulnerable (if the application logic builds the filter insecurely, e.g., eval())
// const userInput = "{ '$ne': null }"; // Imagine this comes from a malicious input
// db.usuarios.find({ "nome": eval(`(${userInput})`) }); // DO NOT DO THIS!

// Secure: MongoDB already parametrizes inputs by default
const userInputNome = "admin";
const userInputSenha = "password";
db.usuarios.find({ "nome": userInputNome, "senha": userInputSenha });
// MongoDB treats 'userInputNome' and 'userInputSenha' as literal values, not as part of the query.

The Power of DBA Outsourcing: Why Your Company Needs It Now

Managing the performance, availability, and security of modern databases—whether SQL or NoSQL—is a Herculean task. It requires a vast body of knowledge, practical experience, and 24/7 dedication. Many medium and large companies try to do this internally, only to find that the cost (in time, money, and risk) is prohibitive. This is where DBA outsourcing with HTI Tecnologia becomes not just an option but an essential strategy.

Unmatched Technical Focus: Our DBAs are dedicated specialists, focused solely on database management. They have in-depth knowledge of various technologies (MySQL, MariaDB, PostgreSQL, Oracle, SQL Server, MongoDB, Redis, Neo4J) and are constantly updated with the latest trends and best practices. This means your performance, availability, and security problems will be solved by those who truly understand the subject, freeing up your internal IT team to focus on your core business competencies.

Risk Reduction and Operational Continuity: With HTI, you eliminate the risk of dependency on a single internal DBA. Our multidisciplinary team ensures that specialists are always available to meet your needs, 24 hours a day, 7 days a week. This translates into greater resilience to failures, rapid responses to incidents, and, consequently, operational continuity for your critical applications. Incidents that could paralyze your operation are quickly resolved by an experienced team.

Cost Optimization and Clear ROI: Hiring and maintaining a highly qualified in-house team of DBAs can be extremely expensive. Outsourcing with HTI Tecnologia offers access to a pool of elite talent for a fraction of the cost, without the need for investments in training, tools, or benefits. The return on investment (ROI) is clear: less downtime, better application performance, and greater security, resulting in savings and a competitive advantage.

If you are looking to optimize the performance of your database environment, I recommend reading our article on CPU in SQL. And to understand even more about how proactive management can prevent problems, check out our page on database monitoring.

Don’t Be Fooled by Superficial Speed

An ultra-fast query is desirable, yes, but only when that speed is not accompanied by hidden costs that compromise the health and integrity of your database. DBAs, DevOps, Tech Leads, and especially IT Managers and CTOs need to look beyond the surface and understand the systemic impact of their queries. Identifying and correcting the 7 hidden signs of a “fast and bad” query is fundamental to ensuring the performance, availability, and security of your data.

At HTI Tecnologia, we are specialists in transforming complex database environments into robust and efficient systems. With our 24/7 consulting, support, and maintenance, we ensure that your queries are not only fast but also healthy, scalable, and secure.

Don’t let a false sense of speed put your business at risk.

Want to uncover the secrets of your database and ensure your queries are truly optimized?

Schedule a meeting with an HTI Tecnologia specialist now and discover how we can fortify your environment and boost your business’s performance!

Schedule a meeting here