chore: import upstream snapshot with attribution
This commit is contained in:
wehub-resource-sync
@@ -0,0 +1,557 @@
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# Database Error Patterns
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Common database errors across PostgreSQL, MySQL, MongoDB, Redis, and SQLite.
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## Connection Errors
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### Connection Refused
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```
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Error: connect ECONNREFUSED 127.0.0.1:5432
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FATAL: connection refused
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```
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**Causes**:
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1. Database server not running
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2. Wrong host/port
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3. Firewall blocking connection
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4. Max connections reached
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**Diagnosis**:
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```bash
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# Check if database is running
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# PostgreSQL
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pg_isready -h localhost -p 5432
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# MySQL
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mysqladmin ping -h localhost
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# Check port
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lsof -i :5432
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netstat -an | grep 5432
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# Check process
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ps aux | grep postgres
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ps aux | grep mysql
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```
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**Solutions**:
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```bash
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# Start database
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# PostgreSQL
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brew services start postgresql # macOS
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sudo systemctl start postgresql # Linux
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# MySQL
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brew services start mysql # macOS
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sudo systemctl start mysql # Linux
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# Docker
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docker start postgres_container
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```
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---
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### Authentication Failed
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```
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FATAL: password authentication failed for user "username"
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Access denied for user 'root'@'localhost'
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```
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**Causes**:
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1. Wrong password
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2. User doesn't exist
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3. Wrong authentication method
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4. User lacks permissions
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**Solutions**:
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```bash
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# PostgreSQL - reset password
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sudo -u postgres psql
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ALTER USER username PASSWORD 'newpassword';
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# MySQL - reset password
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mysql -u root
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ALTER USER 'username'@'localhost' IDENTIFIED BY 'newpassword';
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FLUSH PRIVILEGES;
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# Check pg_hba.conf for auth method (PostgreSQL)
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# Change 'peer' to 'md5' or 'scram-sha-256' for password auth
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```
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---
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### Database Does Not Exist
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```
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FATAL: database "mydb" does not exist
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Unknown database 'mydb'
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```
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**Solutions**:
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```bash
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# PostgreSQL
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createdb mydb
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# Or in psql:
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CREATE DATABASE mydb;
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# MySQL
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mysql -u root -p -e "CREATE DATABASE mydb;"
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# Check existing databases
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psql -l # PostgreSQL
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mysql -e "SHOW DATABASES;" # MySQL
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```
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---
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### Connection Timeout
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```
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Error: Connection timed out
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FATAL: connection timeout expired
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```
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**Causes**:
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1. Network latency
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2. Database overloaded
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3. Firewall issues
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4. DNS resolution slow
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**Solutions**:
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```javascript
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// Increase connection timeout
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// Node.js pg
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const pool = new Pool({
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connectionTimeoutMillis: 10000, // 10 seconds
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})
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// Prisma
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datasource db {
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url = "postgresql://...?connect_timeout=10"
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}
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```
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---
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### Too Many Connections
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```
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FATAL: too many connections for role "postgres"
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ERROR 1040 (HY000): Too many connections
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```
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**Causes**:
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1. Connection leaks (not closing connections)
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2. Pool size too large
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3. Max connections too low
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**Diagnosis**:
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```sql
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-- PostgreSQL
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SELECT count(*) FROM pg_stat_activity;
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SELECT * FROM pg_stat_activity WHERE state = 'idle';
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-- MySQL
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SHOW PROCESSLIST;
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SHOW STATUS LIKE 'Threads_connected';
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```
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**Solutions**:
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```sql
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-- PostgreSQL - increase max connections
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ALTER SYSTEM SET max_connections = 200;
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-- Requires restart
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-- MySQL
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SET GLOBAL max_connections = 200;
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```
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```javascript
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// Use connection pooling properly
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const pool = new Pool({
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max: 20, // Pool size
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idleTimeoutMillis: 30000,
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connectionTimeoutMillis: 2000,
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})
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// Always release connections
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const client = await pool.connect()
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try {
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await client.query('...')
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} finally {
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client.release() // Important!
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}
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```
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---
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## Query Errors
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### Syntax Error
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```
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ERROR: syntax error at or near "FROM"
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You have an error in your SQL syntax
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```
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**Common Causes**:
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1. Missing quotes around strings
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2. Reserved word used as identifier
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3. Missing comma in list
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4. Wrong function name
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**Solutions**:
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```sql
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-- Quote reserved words
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SELECT "order", "user" FROM "table"; -- PostgreSQL
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SELECT `order`, `user` FROM `table`; -- MySQL
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-- Check string quoting
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WHERE name = 'John' -- Correct
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WHERE name = "John" -- Wrong in PostgreSQL (double quotes = identifier)
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```
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---
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### Column Does Not Exist
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```
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ERROR: column "username" does not exist
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Unknown column 'username' in 'field list'
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```
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**Causes**:
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1. Typo in column name
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2. Case sensitivity issue
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3. Column not in table
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4. Wrong table alias
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**Diagnosis**:
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```sql
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-- PostgreSQL
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\d table_name
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-- MySQL
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DESCRIBE table_name;
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SHOW COLUMNS FROM table_name;
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```
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**Solutions**:
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```sql
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-- PostgreSQL is case-sensitive with quoted identifiers
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SELECT "Username" FROM users; -- Looks for exact "Username"
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SELECT username FROM users; -- Looks for lowercase
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-- Check actual columns
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SELECT column_name FROM information_schema.columns
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WHERE table_name = 'users';
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```
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---
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### Relation/Table Does Not Exist
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```
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ERROR: relation "users" does not exist
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Table 'database.users' doesn't exist
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```
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**Causes**:
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1. Table not created
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2. Wrong schema/database
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3. Typo in table name
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4. Migrations not run
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**Solutions**:
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```sql
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-- Check existing tables
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-- PostgreSQL
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\dt
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SELECT table_name FROM information_schema.tables
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WHERE table_schema = 'public';
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-- MySQL
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SHOW TABLES;
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-- Check current schema
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SELECT current_schema(); -- PostgreSQL
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SELECT DATABASE(); -- MySQL
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```
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```bash
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# Run migrations
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npx prisma migrate dev
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npx sequelize-cli db:migrate
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```
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---
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### Constraint Violation
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#### Unique Constraint
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```
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ERROR: duplicate key value violates unique constraint
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Duplicate entry 'value' for key 'PRIMARY'
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```
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**Solutions**:
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```sql
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-- Check for existing value
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SELECT * FROM users WHERE email = 'test@example.com';
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-- Upsert instead of insert
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-- PostgreSQL
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INSERT INTO users (email, name) VALUES ('test@example.com', 'Test')
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ON CONFLICT (email) DO UPDATE SET name = EXCLUDED.name;
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-- MySQL (8.0.20+)
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INSERT INTO users (email, name) VALUES ('test@example.com', 'Test') AS new_values
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ON DUPLICATE KEY UPDATE name = new_values.name;
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```
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#### Foreign Key Constraint
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```
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ERROR: insert or update violates foreign key constraint
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Cannot add or update a child row: a foreign key constraint fails
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```
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**Solutions**:
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```sql
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-- Check if referenced record exists
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SELECT * FROM parent_table WHERE id = 123;
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-- Insert parent first, then child
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INSERT INTO parent_table (id) VALUES (123);
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INSERT INTO child_table (parent_id) VALUES (123);
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-- Or use CASCADE
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ALTER TABLE child_table
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ADD CONSTRAINT fk_parent
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FOREIGN KEY (parent_id) REFERENCES parent_table(id)
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ON DELETE CASCADE;
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```
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#### Not Null Constraint
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```
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ERROR: null value in column "email" violates not-null constraint
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Column 'email' cannot be null
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```
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**Solutions**:
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```sql
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-- Provide value
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INSERT INTO users (name, email) VALUES ('Test', 'test@example.com');
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-- Or add default
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ALTER TABLE users ALTER COLUMN email SET DEFAULT 'default@example.com';
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-- Or make nullable
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ALTER TABLE users ALTER COLUMN email DROP NOT NULL; -- PostgreSQL
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ALTER TABLE users MODIFY email VARCHAR(255) NULL; -- MySQL
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```
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---
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### Deadlock
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```
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ERROR: deadlock detected
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Deadlock found when trying to get lock
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```
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**Causes**:
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1. Transactions waiting on each other
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2. Lock ordering inconsistent
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3. Long-running transactions
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**Solutions**:
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```sql
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-- Always access tables in same order across transactions
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-- Keep transactions short
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BEGIN;
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-- Quick operations only
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COMMIT;
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-- Use appropriate isolation level
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SET TRANSACTION ISOLATION LEVEL READ COMMITTED;
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```
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```javascript
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// Helper function
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const sleep = (ms) => new Promise(resolve => setTimeout(resolve, ms))
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// Retry on deadlock
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async function withRetry(fn, maxRetries = 3) {
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for (let i = 0; i < maxRetries; i++) {
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try {
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return await fn()
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} catch (error) {
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if (error.code === '40P01' && i < maxRetries - 1) { // Deadlock
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await sleep(100 * (i + 1))
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continue
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}
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throw error
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}
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}
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}
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```
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---
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## MongoDB Errors
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### MongoServerSelectionError
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```
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MongoServerSelectionError: connect ECONNREFUSED 127.0.0.1:27017
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```
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**Solutions**:
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```bash
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# Start MongoDB
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brew services start mongodb-community # macOS
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sudo systemctl start mongod # Linux
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# Check status
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mongosh --eval "db.adminCommand('ping')"
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```
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---
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### MongoError: E11000 duplicate key error
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```
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MongoError: E11000 duplicate key error collection: db.users index: email_1
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```
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**Solutions**:
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```javascript
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// Upsert
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await User.findOneAndUpdate(
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{ email: 'test@example.com' },
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{ $set: { name: 'Test' } },
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{ upsert: true }
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)
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// Or handle error
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try {
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await user.save()
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} catch (error) {
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if (error.code === 11000) {
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// Handle duplicate
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}
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}
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```
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---
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### MongooseError: Operation timed out
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```
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MongooseError: Operation `users.find()` buffering timed out after 10000ms
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```
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**Causes**:
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1. Not connected to database
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2. Connection dropped
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3. Query too slow
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**Solutions**:
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```javascript
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// Wait for connection
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await mongoose.connect(uri)
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console.log('Connected to MongoDB')
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// Then start server
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app.listen(3000)
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// Add connection events
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mongoose.connection.on('error', console.error)
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mongoose.connection.on('disconnected', () => {
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console.log('MongoDB disconnected')
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})
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```
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---
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## Redis Errors
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### ECONNREFUSED
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```
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Error: Redis connection to 127.0.0.1:6379 failed - connect ECONNREFUSED
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```
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**Solutions**:
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```bash
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# Start Redis
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brew services start redis # macOS
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sudo systemctl start redis # Linux
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# Test connection
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redis-cli ping
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```
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---
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### WRONGTYPE
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```
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WRONGTYPE Operation against a key holding the wrong kind of value
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```
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**Causes**:
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1. Key exists with different type
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2. Using wrong command for data type
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**Solutions**:
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```bash
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# Check key type
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TYPE mykey
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# Delete and recreate with correct type
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DEL mykey
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```
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---
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### OOM command not allowed
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```
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OOM command not allowed when used memory > 'maxmemory'
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```
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**Solutions**:
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```bash
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# Increase max memory
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redis-cli CONFIG SET maxmemory 2gb
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# Set eviction policy
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redis-cli CONFIG SET maxmemory-policy allkeys-lru
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# In redis.conf
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maxmemory 2gb
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maxmemory-policy allkeys-lru
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```
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---
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## Quick Reference Table
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| Error | Database | Quick Fix |
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|-------|----------|-----------|
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| Connection refused | All | Start database service |
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| Auth failed | All | Check credentials, reset password |
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| DB doesn't exist | All | Create database |
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| Too many connections | All | Use connection pooling |
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| Unique constraint | All | Use upsert |
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| Foreign key violation | All | Insert parent first |
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| Deadlock | All | Retry with backoff |
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| E11000 duplicate | MongoDB | Use findOneAndUpdate with upsert |
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| WRONGTYPE | Redis | Check key type with TYPE |
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Reference in New Issue
Block a user