PostgreSQL with Deno - Performance & Optimization

Performance: PostgreSQL with Deno

MEDIUM IMPACT

This affects server response time and data fetching speed, impacting how fast the frontend receives data to render.

Fetching data from PostgreSQL in a Deno app

Deno

import { Client } from "https://deno.land/x/postgres/mod.ts";

const client = new Client();
await client.connect();

const ids = Array.from({ length: 100 }, (_, i) => i + 1);
const queries = ids.map(id => client.queryArray("SELECT * FROM users WHERE id = $1", id));
const results = await Promise.all(queries);
results.forEach(result => console.log(result.rows));

await client.end();

Runs queries in parallel, reducing total wait time and improving server response speed.

📈 Performance GainReduces total query time by parallelizing, lowering LCP and backend blocking.

Fetching data from PostgreSQL in a Deno app

Deno

import { Client } from "https://deno.land/x/postgres/mod.ts";

const client = new Client();
await client.connect();

for (let i = 0; i < 100; i++) {
  const result = await client.queryArray("SELECT * FROM users WHERE id = $1", i + 1);
  console.log(result.rows);
}

await client.end();

Opening a single connection and running many sequential queries blocks the event loop and delays response.

📉 Performance CostBlocks event loop for each query, causing slow response and higher LCP.

Performance Comparison

Pattern	Server Processing	Network Delay	Browser Impact	Verdict
Sequential queries on single connection	High CPU wait, blocking	Longer wait for data	Delays LCP	[X] Bad
Parallel queries with single connection	Reduced wait time	Faster data transfer	Improves LCP	[!] OK
New connection per request	High overhead per request	Slower response	Delays LCP	[X] Bad
Connection pooling reused	Low overhead	Fast response	Best LCP	[OK] Good

Rendering Pipeline

Database queries run on the server before sending data to the browser. Slow queries delay server response, which delays the browser's first contentful paint.

→Server Processing

→Network Transfer

→Browser Rendering

⚠️ BottleneckServer Processing (database query execution and connection management)

Core Web Vital Affected

LCP

This affects server response time and data fetching speed, impacting how fast the frontend receives data to render.

Optimization Tips

1Use connection pooling to reduce connection overhead.

2Run independent queries in parallel to reduce total wait time.

3Avoid creating and closing database connections on every request.

Performance Quiz - 3 Questions

What is a performance benefit of using connection pooling with PostgreSQL in Deno?

A Reduces connection setup overhead and speeds up server response

B Increases the number of connections to the database

C Makes queries run sequentially to avoid conflicts

D Blocks the event loop to ensure data consistency

DevTools: Network

How to check: Open DevTools > Network tab, reload page, and check the time for the main data API request.

What to look for: Look for long server response times indicating slow database queries or connection overhead.

Practice

1. What is the main purpose of using the Client from the postgres module in Deno?

easy

A. To manage file uploads in Deno

B. To create a web server in Deno

C. To connect to a PostgreSQL database and run queries

D. To handle user authentication in Deno

Solution

1. Step 1: Understand the role of Client in postgres module

   The Client is designed to establish a connection to a PostgreSQL database and execute SQL queries.

2. Step 2: Compare with other options

   Creating web servers, managing file uploads, and handling authentication are unrelated to the Client in the postgres module.

3. Final Answer:

   To connect to a PostgreSQL database and run queries -> Option C

4. Quick Check:

   Client connects to DB and runs queries = C [OK]

Hint: Remember: Client is for DB connection and queries [OK]

Common Mistakes:

• Confusing Client with web server modules
• Thinking Client handles file uploads
• Assuming Client manages user authentication

2. Which of the following is the correct way to import the PostgreSQL client in a Deno script?

easy

A. import * as Client from "postgres";

B. import Client from "postgres";

C. const Client = require('postgres');

D. import { Client } from "https://deno.land/x/postgres@v0.17.0/mod.ts";

Solution

1. Step 1: Identify correct import syntax for Deno modules

   Deno uses ES module syntax with full URLs for third-party modules, so import must include the URL and version.

2. Step 2: Check each option

   import { Client } from "https://deno.land/x/postgres@v0.17.0/mod.ts"; uses correct ES module import with URL and version. Options B, C, and D use Node.js style or incomplete imports not valid in Deno.

3. Final Answer:

   import { Client } from "https://deno.land/x/postgres@v0.17.0/mod.ts"; -> Option D

4. Quick Check:

   Deno imports use full URLs = A [OK]

Hint: Deno imports need full URL with version [OK]

Common Mistakes:

• Using Node.js require() syntax
• Omitting the full URL in import
• Using wildcard import incorrectly

3. Given the following Deno code snippet, what will be the output?

import { Client } from "https://deno.land/x/postgres@v0.17.0/mod.ts";

const client = new Client({ user: "user", database: "testdb" });
await client.connect();
const result = await client.queryObject("SELECT 1 AS number");
await client.end();
console.log(result.rows[0].number);

medium

A. undefined

B. 1

C. Error: Connection not established

D. null

Solution

1. Step 1: Analyze the query execution

   The code connects to the database, runs a query selecting the number 1 as 'number', then closes the connection.

2. Step 2: Understand the result object

   The queryObject method returns an object with a rows array. The first row's 'number' field contains 1, so logging it prints 1.

3. Final Answer:

   1 -> Option B

4. Quick Check:

   Query returns 1, printed output = 1 [OK]

Hint: Query returns 1, check rows[0].number for output [OK]

Common Mistakes:

• Forgetting to await client.connect()
• Accessing wrong property of result
• Not closing the client connection

4. Identify the error in this Deno PostgreSQL code snippet:

import { Client } from "https://deno.land/x/postgres@v0.17.0/mod.ts";

const client = new Client({ user: "user", database: "testdb" });
const result = await client.queryObject("SELECT NOW()");
await client.end();
console.log(result.rows);

medium

A. Missing await client.connect() before query

B. Incorrect import statement

C. Using queryObject instead of query

D. Calling client.end() before query

Solution

1. Step 1: Check connection setup

   The code creates a client but never calls await client.connect() before running the query.

2. Step 2: Understand consequences

   Without connecting, the query will fail because the client is not connected to the database.

3. Final Answer:

   Missing await client.connect() before query -> Option A

4. Quick Check:

   Must connect before queries = D [OK]

Hint: Always connect client before running queries [OK]

Common Mistakes:

• Skipping client.connect() call
• Calling client.end() too early
• Confusing queryObject with query

5. You want to insert multiple rows into a PostgreSQL table using Deno's postgres client efficiently. Which approach is best to avoid multiple separate queries and ensure all rows are inserted in one operation?

hard

A. Use a single parameterized query with multiple VALUES tuples

B. Call client.queryObject() multiple times, once per row

C. Run a loop with client.connect() and client.end() for each row

D. Insert rows one by one without parameters

Solution

1. Step 1: Understand batch insertion

   Inserting multiple rows in one query reduces overhead and improves performance.

2. Step 2: Evaluate options

   A uses a single parameterized query with multiple VALUES tuples, which is efficient and safe. B runs multiple queries, increasing overhead. C reconnects repeatedly, which is inefficient. D risks SQL injection and is inefficient.

3. Final Answer:

   Use a single parameterized query with multiple VALUES tuples -> Option A

4. Quick Check:

   Batch insert with one query = A [OK]

Hint: Batch inserts use one query with multiple VALUES [OK]

Common Mistakes:

• Running many separate queries instead of one
• Opening and closing connection repeatedly
• Not using parameterized queries risking SQL injection