Database Troubleshooting Guide

This guide provides comprehensive commands, techniques, and solutions for troubleshooting common database issues across various database systems including MySQL, PostgreSQL, MongoDB, and Redis.

MySQL Troubleshooting
PostgreSQL Troubleshooting
MongoDB Troubleshooting
Redis Troubleshooting
General Database Performance
Connection Issues
Backup and Recovery
Common Scenarios

MySQL Troubleshooting

Server Status and Information

# Check if MySQL is running
sudo systemctl status mysql

# Get MySQL server version
mysql -V

# Connect to MySQL server
mysql -u username -p -h hostname

# Show MySQL server status
mysqladmin -u username -p status

# Get detailed server status
mysqladmin -u username -p extended-status

# Check MySQL process list
mysql -u username -p -e "SHOW PROCESSLIST"

# Check MySQL server variables
mysql -u username -p -e "SHOW VARIABLES"

Performance and Slow Queries

# Enable slow query log (add to my.cnf)
slow_query_log = 1
slow_query_log_file = /var/log/mysql/mysql-slow.log
long_query_time = 2

# Check if slow query log is enabled
mysql -u username -p -e "SHOW VARIABLES LIKE 'slow_query%'"

# Analyze slow query log
mysqldumpslow /var/log/mysql/mysql-slow.log

# Use the MySQL performance schema
mysql -u username -p -e "SELECT * FROM performance_schema.events_statements_summary_by_digest ORDER BY sum_timer_wait DESC LIMIT 10"

# Check table statistics
mysql -u username -p -e "SHOW TABLE STATUS FROM database_name"

# Show InnoDB status
mysql -u username -p -e "SHOW ENGINE INNODB STATUS\G"

Resource Utilization

# Check max connections and current connections
mysql -u username -p -e "SHOW VARIABLES LIKE 'max_connections'"
mysql -u username -p -e "SHOW STATUS LIKE 'Max_used_connections'"

# Check buffer and cache sizes
mysql -u username -p -e "SHOW VARIABLES LIKE '%buffer%'"
mysql -u username -p -e "SHOW VARIABLES LIKE '%cache%'"

# Check memory usage
mysql -u username -p -e "SELECT * FROM performance_schema.memory_summary_global_by_event_name ORDER BY current_alloc DESC LIMIT 10"

Database and Table Maintenance

# Check and repair tables
mysqlcheck -u username -p --check database_name
mysqlcheck -u username -p --repair database_name

# Optimize tables
mysqlcheck -u username -p --optimize database_name

# Analyze tables
mysqlcheck -u username -p --analyze database_name

# Show table index statistics
mysql -u username -p -e "SHOW INDEX FROM database_name.table_name"

# Check for fragmented tables
mysql -u username -p -e "SELECT table_name, data_free, engine FROM information_schema.tables WHERE table_schema='database_name' AND data_free > 0"

PostgreSQL Troubleshooting

Server Status and Information

# Check if PostgreSQL is running
sudo systemctl status postgresql

# Get PostgreSQL version
psql --version

# Connect to PostgreSQL server
psql -U username -h hostname -d database_name

# Show PostgreSQL server status
pg_ctl status -D /path/to/data/directory

# Check PostgreSQL configuration
sudo cat /etc/postgresql/version/main/postgresql.conf

# List PostgreSQL databases
psql -U username -c "\l"

# List PostgreSQL users
psql -U username -c "\du"

Performance and Slow Queries

# Enable query logging (add to postgresql.conf)
log_min_duration_statement = 200  # ms

# Check currently running queries
psql -U username -c "SELECT pid, age(clock_timestamp(), query_start), usename, query FROM pg_stat_activity WHERE query != '<IDLE>' AND query NOT ILIKE '%pg_stat_activity%' ORDER BY query_start desc;"

# Kill a long-running query
psql -U username -c "SELECT pg_cancel_backend(pid);"

# Find the slowest queries
psql -U username -c "SELECT substring(query, 1, 50) AS short_query, round(total_exec_time::numeric, 2) AS total_exec_time, calls, round(mean_exec_time::numeric, 2) AS mean, round((100 * total_exec_time / sum(total_exec_time::numeric) OVER ())::numeric, 2) AS percentage FROM pg_stat_statements ORDER BY total_exec_time DESC LIMIT 10;"

# Show table statistics
psql -U username -c "SELECT * FROM pg_stat_user_tables;"

# Show index usage statistics
psql -U username -c "SELECT * FROM pg_stat_user_indexes;"

Resource Utilization

# Check database size
psql -U username -c "SELECT pg_size_pretty(pg_database_size('database_name'));"

# Check table sizes
psql -U username -d database_name -c "SELECT table_name, pg_size_pretty(pg_total_relation_size(quote_ident(table_name))) AS total_size FROM information_schema.tables WHERE table_schema = 'public' ORDER BY pg_total_relation_size(quote_ident(table_name)) DESC;"

# Check index sizes
psql -U username -d database_name -c "SELECT indexname, pg_size_pretty(pg_relation_size(indexname::text)) AS index_size FROM pg_indexes WHERE schemaname = 'public' ORDER BY pg_relation_size(indexname::text) DESC;"

# Monitor connections
psql -U username -c "SELECT count(*), datname, usename, client_addr FROM pg_stat_activity GROUP BY datname, usename, client_addr;"

# Check connection limits
psql -U username -c "SHOW max_connections;"
psql -U username -c "SELECT count(*) FROM pg_stat_activity;"

Database and Table Maintenance

# Vacuum a database
vacuumdb -U username database_name

# Vacuum analyze a specific table
psql -U username -d database_name -c "VACUUM ANALYZE table_name;"

# Full vacuum
psql -U username -d database_name -c "VACUUM FULL table_name;"

# Reindex a table
psql -U username -d database_name -c "REINDEX TABLE table_name;"

# Reindex a database
reindexdb -U username database_name

# Check for bloat
psql -U username -d database_name -c "SELECT schemaname, tablename, pg_size_pretty(bloat_size) as bloat_size, pg_size_pretty(table_size) as actual_size, bloat_ratio FROM (SELECT *, table_size-bloat_size AS actual_table_size, round(bloat_size*100/table_size) AS bloat_ratio FROM (SELECT schemaname, tablename, pg_total_relation_size(schemaname || '.' || tablename) AS table_size, ((record_count+CASE WHEN current_setting('block_size')::numeric > 8192 THEN 1 ELSE 0 END)/((bs-page_hdr)/tpl_size)-(sub_pages+CASE WHEN page_hdr>sub_page_hdr THEN 1 ELSE 0 END)) AS bloat_size FROM (SELECT heap.nspname AS schemaname, heap.relname AS tablename, bs, tpl_data_size, tpl_hdr_size, index_tuple_hdr_size, block_size, ma-4 AS page_hdr, block_size-ma - CASE WHEN version >= 80000 THEN block_size/32 ELSE 0 END AS sub_page_hdr, heap.n_tuples AS record_count, count(heap.n_tuples) / (ma/block_size::float) AS sub_pages, ceil(heap.reltuples/floor((block_size-page_hdr-1)/max(index_tuple_hdr_size, tpl_hdr_size+tpl_data_size))) + ceil(heap.reltuples/floor((block_size-page_hdr-1)/(tpl_hdr_size+1))) AS totalpages, block_size, block_size - 24 - ma - CASE WHEN 8 < block_size/10 THEN 8 ELSE block_size/10 END AS tpl_size FROM (SELECT heap.nspname, heap.relname, heap.reltuples, heap.relpages, heap.relkind, bs, tpl_data_size, tpl_hdr_size, index_tuple_hdr_size, block_size, version, ma, setting FROM (SELECT ns.nspname, rel.relname, rel.reltuples, rel.relpages, rel.relkind, (datawidth + (hdr_width + ma - (case when hdr_width % ma = 0 THEN ma ELSE hdr_width % ma END))) + nullhdr2 AS tpl_data_size, 32 AS tpl_hdr_size, 8 AS index_tuple_hdr_size FROM (SELECT hdr + ma-case when hdr%ma=0 THEN ma ELSE hdr%ma END + CASE WHEN oou.attlen > 0 THEN ma-case when ma%oou.attlen=0 THEN ma ELSE ma%oou.attlen END ELSE 0 END AS datawidth, hdr, ma, ns.nspname, rel.relname, reltuples, relpages, relkind FROM (SELECT ma, sum((1-case when attnotnull THEN 0 ELSE 1 END)*ma) AS hdr, ns.nspname, rel.relname, rel.reltuples, rel.relpages, rel.relkind, sum((CASE WHEN atttypid in (ARRAY[1042, 1043]) THEN atttypmod-4 WHEN atttypid in (ARRAY[16, 17, 18, 19, 20, 21, 23, 26, 700, 701, 704, 869, 1082, 1083, 1266, 1700]) THEN getwidth(atttypid) ELSE getwidth(CASE WHEN atttypid IN(ARRAY[1700]) THEN 842 ELSE atttypid END)*(CASE WHEN attlen > 0 THEN attlen ELSE 10 END) END)*(attnotnull+0)) FROM pg_catalog.pg_attribute att JOIN pg_catalog.pg_type typ ON att.atttypid = typ.oid JOIN pg_catalog.pg_class rel ON att.attrelid = rel.oid JOIN pg_catalog.pg_namespace ns ON rel.relnamespace = ns.oid JOIN (SELECT attrelid, max(attnum) as attnum FROM pg_catalog.pg_attribute GROUP BY attrelid) aa ON att.attrelid=aa.attrelid AND att.attnum<=aa.attnum WHERE ns.nspname NOT IN ('pg_catalog','information_schema') AND rel.relkind in ('r','t') AND att.attnum > 0 GROUP BY ma, ns.nspname, rel.relname, rel.reltuples, rel.relpages, rel.relkind ORDER BY ns.nspname, rel.relname, ma) sp JOIN pg_catalog.pg_attribute oou ON sp.relname=oou.attrelid::regclass::text AND oou.attnum = 1) oou, (SELECT current_setting('block_size')::numeric BS) bs) rel, (SELECT count(*) bloat, ma, bs FROM pg_catalog.pg_attribute GROUP BY 2,3) ma_table, (SELECT current_setting('block_size')::numeric BS) bs, version()) AS subq) as heap, (SELECT current_setting('block_size')::numeric BS) bs WHERE schemaname='public') AS tables WHERE bloat_ratio >= 30 AND table_size > 1024 * 1024 * 10 ORDER BY bloat_size DESC LIMIT 10;"

MongoDB Troubleshooting

Server Status and Information

# Check if MongoDB is running
sudo systemctl status mongod

# Get MongoDB version
mongod --version

# Connect to MongoDB server
mongo --host hostname

# Check MongoDB server status
mongo --eval "db.serverStatus()"

# Show MongoDB databases
mongo --eval "show dbs"

# Show MongoDB collections
mongo database_name --eval "show collections"

# Check MongoDB replica set status
mongo --eval "rs.status()"

Performance and Slow Queries

# Enable profiling for slow queries
mongo --eval "db.setProfilingLevel(1, 100)" # Profile queries slower than 100ms

# Check profiling status
mongo --eval "db.getProfilingStatus()"

# View slow queries
mongo --eval "db.system.profile.find().pretty()"

# Get current operations
mongo --eval "db.currentOp()"

# Kill a specific operation
mongo --eval "db.killOp(opid)"

# View database statistics
mongo --eval "db.stats()"

# View collection statistics
mongo --eval "db.collection_name.stats()"

Index Management

# Show collection indexes
mongo --eval "db.collection_name.getIndexes()"

# Create an index
mongo --eval "db.collection_name.createIndex({field_name: 1})"

# Explain a query
mongo --eval "db.collection_name.find({query}).explain('executionStats')"

# Check index usage
mongo --eval "db.collection_name.aggregate([{$indexStats: {}}])"

# Remove an index
mongo --eval "db.collection_name.dropIndex('index_name')"

Resource Utilization

# Check memory usage
mongo --eval "db.serverStatus().mem"

# Check connections
mongo --eval "db.serverStatus().connections"

# Check network traffic
mongo --eval "db.serverStatus().network"

# Check operation counters
mongo --eval "db.serverStatus().opcounters"

# Check lock information
mongo --eval "db.serverStatus().locks"

Redis Troubleshooting

Server Status and Information

# Check if Redis is running
sudo systemctl status redis

# Get Redis version
redis-cli --version

# Connect to Redis server
redis-cli -h hostname -p port -a password

# Check Redis server info
redis-cli info

# Monitor Redis commands in real-time
redis-cli monitor

# Check Redis memory usage
redis-cli info memory

# Check Redis clients
redis-cli info clients

Performance Monitoring

# Check slow log
redis-cli slowlog get 10

# Get statistics about keys
redis-cli --stat

# Check command statistics
redis-cli info commandstats

# Scan for big keys
redis-cli --bigkeys

# Check latency
redis-cli --latency

# Run Redis benchmark
redis-benchmark -h hostname -p port -c 50 -n 10000 -q

Memory Management

# Check memory usage breakdown
redis-cli memory stats

# Find memory usage of a key
redis-cli memory usage key_name

# Check if Redis is swapping
redis-cli info stats | grep process_id
cat /proc/$(redis-cli info stats | grep process_id | cut -d: -f2)/smaps | grep -i swap

# Check maxmemory policy
redis-cli config get maxmemory-policy

# Set maxmemory policy
redis-cli config set maxmemory-policy allkeys-lru

# Flush all data (use with caution)
redis-cli flushall

Replication and Cluster

# Check replication status
redis-cli info replication

# Check cluster status
redis-cli cluster info

# List cluster nodes
redis-cli cluster nodes

# Check for cluster errors
redis-cli cluster check hostname:port

# Manually failover
redis-cli -h master_host -p master_port cluster failover

General Database Performance

Query Optimization Tips

Proper Indexing
- Create indexes on frequently queried columns
- Avoid over-indexing (indexes consume space and slow down writes)
- Use composite indexes for multi-column queries
Query Structure
- Use specific column names instead of SELECT *
- Limit result sets
- Use appropriate JOIN types
- Avoid unnecessary subqueries
Connection Pooling
- Implement connection pooling to reduce connection overhead
- Monitor connection usage and optimize pool size
Caching Strategies
- Use query caching where appropriate
- Implement application-level caching for frequent queries
- Consider Redis or Memcached for caching layers
Regular Maintenance
- Schedule regular vacuum/analyze operations
- Monitor and manage database growth
- Purge old data or archive to secondary storage

Connection Issues

Common Connection Problems

# Check network connectivity
telnet hostname port

# Verify firewall settings
sudo iptables -L

# Check listening ports
sudo netstat -tulpn | grep LISTEN

# Test DNS resolution
nslookup hostname

# Check SSL/TLS certificates
openssl s_client -connect hostname:port

# Check database logs for connection errors
tail -f /var/log/mysql/error.log    # MySQL
tail -f /var/log/postgresql/postgresql-version-main.log    # PostgreSQL
tail -f /var/log/mongodb/mongod.log    # MongoDB
tail -f /var/log/redis/redis-server.log    # Redis

Authentication Issues

# Reset MySQL root password
sudo systemctl stop mysql
sudo mysqld_safe --skip-grant-tables &
mysql -u root
mysql> USE mysql;
mysql> UPDATE user SET authentication_string=PASSWORD('new_password') WHERE User='root';
mysql> FLUSH PRIVILEGES;
mysql> quit;
sudo systemctl start mysql

# Reset PostgreSQL password
sudo -u postgres psql
postgres=# ALTER USER username WITH PASSWORD 'new_password';

# Check MongoDB authentication
mongo --eval "db.getUsers()"

# Reset Redis password
redis-cli config set requirepass "new_password"

Backup and Recovery

Backup Commands

# MySQL backup
mysqldump -u username -p database_name > backup.sql
mysqldump -u username -p --all-databases > full_backup.sql

# PostgreSQL backup
pg_dump -U username database_name > backup.sql
pg_dumpall -U username > full_backup.sql

# MongoDB backup
mongodump --host hostname --db database_name --out backup_directory
mongodump --host hostname --out backup_directory

# Redis backup
redis-cli save    # Synchronous save
redis-cli bgsave    # Asynchronous save

Recovery Commands

# MySQL recovery
mysql -u username -p database_name < backup.sql

# PostgreSQL recovery
psql -U username database_name < backup.sql

# MongoDB recovery
mongorestore --host hostname --db database_name backup_directory/database_name

# Redis recovery
# Redis automatically loads the dump.rdb file on restart

Point-in-Time Recovery

# MySQL binary log recovery
mysqlbinlog binlog.000001 | mysql -u username -p

# PostgreSQL WAL recovery
# Edit recovery.conf:
restore_command = 'cp /path/to/archive/%f %p'
recovery_target_time = '2023-01-01 12:00:00'

# MongoDB oplog replay
mongorestore --host hostname --oplogReplay

Common Scenarios

Scenario 1: MySQL High CPU Usage

Symptoms:

High server load
Slow query responses
Many running processes

Diagnosis:

# Check current processes
mysql -u username -p -e "SHOW PROCESSLIST" | grep -v Sleep

# Find slow queries
tail -f /var/log/mysql/mysql-slow.log

# Check query cache hit rate
mysql -u username -p -e "SHOW GLOBAL STATUS LIKE 'Qcache%'"

Solution:

Optimize problematic queries

EXPLAIN SELECT * FROM large_table WHERE non_indexed_column = 'value';
# Add appropriate indexes based on EXPLAIN output
ALTER TABLE large_table ADD INDEX (non_indexed_column);

Adjust MySQL configuration

# Add to my.cnf
innodb_buffer_pool_size = 4G  # Adjust based on server memory
query_cache_type = 1
query_cache_size = 128M

Implement connection pooling at application level

Scenario 2: PostgreSQL Database Bloat

Symptoms:

Increasing disk usage
Slower query performance over time
High I/O activity during queries

Diagnosis:

# Check table and index sizes
psql -U username -d database_name -c "SELECT pg_size_pretty(pg_total_relation_size('table_name'));"

# Check for bloat
psql -U username -d database_name -c "SELECT schemaname, tablename, pg_size_pretty(bloat_size) AS bloat_size, pg_size_pretty(table_size) AS actual_size, bloat_ratio FROM (SELECT *, table_size-bloat_size AS actual_table_size, round(bloat_size*100/table_size) AS bloat_ratio FROM (SELECT schemaname, tablename, pg_total_relation_size(schemaname || '.' || tablename) AS table_size, ((record_count+CASE WHEN current_setting('block_size')::numeric > 8192 THEN 1 ELSE 0 END)/((bs-page_hdr)/tpl_size)-(sub_pages+CASE WHEN page_hdr>sub_page_hdr THEN 1 ELSE 0 END)) AS bloat_size FROM (SELECT heap.nspname AS schemaname, heap.relname AS tablename, bs, tpl_data_size, tpl_hdr_size, index_tuple_hdr_size, block_size, ma-4 AS page_hdr, block_size-ma - CASE WHEN version >= 80000 THEN block_size/32 ELSE 0 END AS sub_page_hdr, heap.n_tuples AS record_count, count(heap.n_tuples) / (ma/block_size::float) AS sub_pages, ceil(heap.reltuples/floor((block_size-page_hdr-1)/max(index_tuple_hdr_size, tpl_hdr_size+tpl_data_size))) + ceil(heap.reltuples/floor((block_size-page_hdr-1)/(tpl_hdr_size+1))) AS totalpages, block_size, block_size - 24 - ma - CASE WHEN 8 < block_size/10 THEN 8 ELSE block_size/10 END AS tpl_size FROM (SELECT heap.nspname, heap.relname, heap.reltuples, heap.relpages, heap.relkind, bs, tpl_data_size, tpl_hdr_size, index_tuple_hdr_size, block_size, version, ma, setting FROM (SELECT ns.nspname, rel.relname, rel.reltuples, rel.relpages, rel.relkind, (datawidth + (hdr_width + ma - (case when hdr_width % ma = 0 THEN ma ELSE hdr_width % ma END))) + nullhdr2 AS tpl_data_size, 32 AS tpl_hdr_size, 8 AS index_tuple_hdr_size FROM (SELECT hdr + ma-case when hdr%ma=0 THEN ma ELSE hdr%ma END + CASE WHEN oou.attlen > 0 THEN ma-case when ma%oou.attlen=0 THEN ma ELSE ma%oou.attlen END ELSE 0 END AS datawidth, hdr, ma, ns.nspname, rel.relname, reltuples, relpages, relkind FROM (SELECT ma, sum((1-case when attnotnull THEN 0 ELSE 1 END)*ma) AS hdr, ns.nspname, rel.relname, rel.reltuples, rel.relpages, rel.relkind, sum((CASE WHEN atttypid in (ARRAY[1042, 1043]) THEN atttypmod-4 WHEN atttypid in (ARRAY[16, 17, 18, 19, 20, 21, 23, 26, 700, 701, 704, 869, 1082, 1083, 1266, 1700]) THEN getwidth(atttypid) ELSE getwidth(CASE WHEN atttypid IN(ARRAY[1700]) THEN 842 ELSE atttypid END)*(CASE WHEN attlen > 0 THEN attlen ELSE 10 END) END)*(attnotnull+0)) FROM pg_catalog.pg_attribute att JOIN pg_catalog.pg_type typ ON att.atttypid = typ.oid JOIN pg_catalog.pg_class rel ON att.attrelid = rel.oid JOIN pg_catalog.pg_namespace ns ON rel.relnamespace = ns.oid JOIN (SELECT attrelid, max(attnum) as attnum FROM pg_catalog.pg_attribute GROUP BY attrelid) aa ON att.attrelid=aa.attrelid AND att.attnum<=aa.attnum WHERE ns.nspname NOT IN ('pg_catalog','information_schema') AND rel.relkind in ('r','t') AND att.attnum > 0 GROUP BY ma, ns.nspname, rel.relname, rel.reltuples, rel.relpages, rel.relkind ORDER BY ns.nspname, rel.relname, ma) sp JOIN pg_catalog.pg_attribute oou ON sp.relname=oou.attrelid::regclass::text AND oou.attnum = 1) oou, (SELECT current_setting('block_size')::numeric BS) bs) rel, (SELECT count(*) bloat, ma, bs FROM pg_catalog.pg_attribute GROUP BY 2,3) ma_table, (SELECT current_setting('block_size')::numeric BS) bs, version()) AS subq) as heap, (SELECT current_setting('block_size')::numeric BS) bs WHERE schemaname='public') AS tables WHERE bloat_ratio >= 30 AND table_size > 1024 * 1024 ORDER BY bloat_size DESC LIMIT 10;"

Solution:

Perform regular vacuum operations

# Regular vacuum (can run while system is online)
VACUUM ANALYZE table_name;

# Full vacuum (exclusive lock, reclaims more space)
VACUUM FULL table_name;

Adjust autovacuum settings

# Add to postgresql.conf
autovacuum = on
autovacuum_vacuum_threshold = 50
autovacuum_analyze_threshold = 50
autovacuum_vacuum_scale_factor = 0.1
autovacuum_analyze_scale_factor = 0.05

Reindex tables
```
REINDEX TABLE table_name;
```

Scenario 3: MongoDB High Memory Usage

Symptoms:

MongoDB using excessive RAM
Slow query performance
High read/write latency

Diagnosis:

# Check current memory usage
mongo --eval "db.serverStatus().mem"

# Check working set size
mongo --eval "db.serverStatus().wiredTiger.cache['bytes currently in the cache']"

# Identify largest collections
mongo --eval "db.stats()" database_name

# Check index sizes
mongo --eval "db.collection_name.stats().indexSizes"

Solution:

Limit MongoDB cache size

# Add to mongod.conf
wiredTiger:
  engineConfig:
    cacheSizeGB: 2  # Set appropriate value based on server memory

Optimize or remove unnecessary indexes

# Find unused indexes
mongo --eval "db.collection_name.aggregate([{$indexStats: {}}])"

# Remove unused indexes
mongo --eval "db.collection_name.dropIndex('unused_index_name')"

Consider sharding for very large datasets

# Enable sharding for a database
mongo --eval "sh.enableSharding('database_name')"

# Shard a collection
mongo --eval "sh.shardCollection('database_name.collection_name', {shard_key: 1})"

Scenario 4: Redis Connection Overload

Symptoms:

"Max number of clients reached" errors
Slow response times
Connection timeouts

Diagnosis:

# Check current connections
redis-cli info clients

# Check max clients setting
redis-cli config get maxclients

# Monitor client connections in real-time
redis-cli --stat

Solution:

Increase maximum clients

# Temporarily
redis-cli config set maxclients 10000

# Permanently in redis.conf
maxclients 10000

Implement proper connection pooling in application

# Example in Python using redis-py with connection pooling
import redis

pool = redis.ConnectionPool(host='hostname', port=6379, db=0, max_connections=100)
r = redis.Redis(connection_pool=pool)

Identify and fix clients that aren't properly closing connections

# List client connections and their idle times
redis-cli client list

# Set timeout for idle connections in redis.conf
timeout 300

Remember to always back up your database before making significant changes, especially in production environments. The commands and techniques in this guide should be tested in a development environment first before applying to production systems.

Navigation Menu

Database Troubleshooting Guide

Table of Contents

MySQL Troubleshooting

Server Status and Information

Performance and Slow Queries

Resource Utilization

Database and Table Maintenance

PostgreSQL Troubleshooting

Server Status and Information

Performance and Slow Queries

Resource Utilization

Database and Table Maintenance

MongoDB Troubleshooting

Server Status and Information

Performance and Slow Queries

Index Management

Resource Utilization

Redis Troubleshooting

Server Status and Information

Performance Monitoring

Memory Management

Replication and Cluster

General Database Performance

Query Optimization Tips

Connection Issues

Common Connection Problems

Authentication Issues

Backup and Recovery

Backup Commands

Recovery Commands

Point-in-Time Recovery

Common Scenarios

Scenario 1: MySQL High CPU Usage

Scenario 2: PostgreSQL Database Bloat

Scenario 3: MongoDB High Memory Usage

Scenario 4: Redis Connection Overload

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Database Troubleshooting Guide

Table of Contents

MySQL Troubleshooting

Server Status and Information

Performance and Slow Queries

Resource Utilization

Database and Table Maintenance

PostgreSQL Troubleshooting

Server Status and Information

Performance and Slow Queries

Resource Utilization

Database and Table Maintenance

MongoDB Troubleshooting

Server Status and Information

Performance and Slow Queries

Index Management

Resource Utilization

Redis Troubleshooting

Server Status and Information

Performance Monitoring

Memory Management

Replication and Cluster

General Database Performance

Query Optimization Tips

Connection Issues

Common Connection Problems

Authentication Issues

Backup and Recovery

Backup Commands

Recovery Commands

Point-in-Time Recovery

Common Scenarios

Scenario 1: MySQL High CPU Usage

Scenario 2: PostgreSQL Database Bloat

Scenario 3: MongoDB High Memory Usage

Scenario 4: Redis Connection Overload