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What is the architecture of PostgreSQL?
Question: Can you explain the architecture of PostgreSQL?
Answer: PostgreSQL has a client-server architecture that includes:
Postmaster: The main server process managing connections.
Shared Buffers: Stores frequently accessed data for faster operations.
Background Processes: Includes processes like WAL writer, autovacuum, and stats collector.
Storage Layer: Manages data files and WAL logs for durability.
Libpq: The communication interface between the client and the server.
How do you optimize slow queries in PostgreSQL?
Question: How do you identify and optimize slow queries?
Answer:
Analyze with EXPLAIN/EXPLAIN ANALYZE: Shows the query execution plan.
Indexing: Add indexes to columns frequently used in WHERE, JOIN, or GROUP BY.
Vacuum and Analyze: Regularly optimize table statistics.
Rewrite Queries: Simplify complex queries or break them into smaller ones.
Partitioning: Use table partitioning for large datasets.
What are the differences between physical and logical replication?
Question: Can you explain the differences between physical and logical replication?
Answer:
Physical Replication:
Copies the entire database cluster.
Used for standby servers.
Operates at the WAL level.
Logical Replication:
Replicates individual tables.
Supports selective replication.
Uses a plugin-based system for decoding.
How do you troubleshoot a PostgreSQL database crash?
Question: What steps do you take to investigate and recover from a database crash?
Answer:
Check Logs: Review postgresql.log for error details.
Verify Disk Space: Ensure enough space for data and WAL logs.
Restart Service: Use pg_ctl or systemctl.
WAL Recovery: Ensure WAL files are intact for recovery.
Inspect Configuration: Check for misconfigurations in postgresql.conf.
Hardware Check: Look for disk or memory failures.
What is the role of pg_hba.conf?
Question: What is pg_hba.conf, and how does it work?
Answer: pg_hba.conf (host-based authentication) controls access to the PostgreSQL database. It specifies:
Host: IP addresses allowed to connect.
Database: Databases that can be accessed.
User: Specific users with access permissions.
Method: Authentication methods like MD5, SCRAM-SHA-256, or trust.
How do you implement connection pooling in PostgreSQL?
Question: How do you set up connection pooling for PostgreSQL?
Answer: Connection pooling reduces the overhead of creating new connections. You can use tools like:
PgBouncer: A lightweight connection pooler for PostgreSQL.
Pgpool-II: Provides connection pooling along with load balancing and replication.
Configuration: Set parameters like max_connections and idle_in_transaction_session_timeout.
What is auto vacuum, and why is it important?
Question: What is the purpose of auto vacuum in PostgreSQL?
Answer: Auto vacuum automatically reclaims storage occupied by dead tuples, updates table statistics, and prevents transaction ID wraparound. It ensures optimal database performance without manual intervention.
How do you upgrade a PostgreSQL cluster?
Question: What methods can you use to upgrade PostgreSQL?
Answer:
In-Place Upgrade (pg_upgrade): Migrates data to the new version with minimal downtime.
Dump and Restore: Uses pg_dump for exporting and importing data.
Logical Replication: Replicates data to a new server running the upgraded version.
What are the common challenges in PostgreSQL replication?
Question: What issues can arise during PostgreSQL replication?
Answer:
Lag in Streaming Replication: Caused by network latency or high transaction volume.
WAL File Retention: Missing or deleted WAL files can break replication.
Configuration Errors: Misconfigured primary_conninfo or recovery.conf.
Disk Space Issues: Insufficient space for WAL files or replication slots.
What are PostgreSQL partitioning and sharding?
Question: What are the differences between partitioning and sharding?
Answer:
Partitioning: Splits a table into smaller, manageable pieces within the same database. Useful for performance optimization.
Sharding: Distributes data across multiple databases or servers. Used for scalability in large systems.
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