System Design - Scalability: Sharding Part 3

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is the main difference between proactive and reactive re-sharding strategies?

Proactive re-sharding anticipates growth and performance issues, while reactive re-sharding responds to detected imbalances or performance degradation.

How does the dual-writes strategy ensure zero-downtime re-sharding?

Dual-writes temporarily write to both old and new shard configurations while reading from the old until migration is complete.

What is the main advantage of the phase-based approach to re-sharding?

The phase-based approach reduces risk and ensures stability by migrating in phases.

How does blue-green deployments ensure zero-downtime re-sharding?

Blue-green deployments maintain two parallel environments to switch traffic seamlessly after the new configuration is fully tested. Signup and view all the answers

What is incremental data copying, and how does it ensure zero-downtime migrations?

Incremental data copying gradually copies data from old shards to new ones in small batches, minimizing impact. Signup and view all the answers

What is the purpose of consistency checks during zero-downtime migrations?

Consistency checks continuously validate data consistency between old and new shards during migration. Signup and view all the answers

How does Facebook's proactive re-sharding strategy manage rapid growth and performance issues?

Facebook proactively re-shards its user data to manage rapid growth and ensure no single shard becomes a bottleneck. Signup and view all the answers

What benefit does Netflix's blue-green deployment strategy provide during database migrations?

Netflix's blue-green deployment strategy allows seamless switching between old and new databases during migration processes. Signup and view all the answers

What approach does Amazon employ to maintain data integrity when moving customer data between different database services?

Consistency checks Signup and view all the answers

What benefit does schema versioning provide in managing database schema changes?

Handling changes without breaking existing queries Signup and view all the answers

What is the primary purpose of having rollback procedures in place during database migration?

Quick recovery in case of issues Signup and view all the answers

What is the main difference between Two-Phase Commit (2PC) and Three-Phase Commit (3PC)?

An extra phase to mitigate the blocking problem Signup and view all the answers

What is the primary advantage of using asynchronous replication in database replication strategies?

Higher performance Signup and view all the answers

What is the purpose of automated failover in a primary-replica configuration?

To switch to a replica if the primary fails Signup and view all the answers

What is the main challenge in dealing with cross-shard queries?

Complexity and latency Signup and view all the answers

What is the primary benefit of using distributed SQL engines in optimizing cross-shard queries?

Efficient execution of queries across shards Signup and view all the answers

What is the key advantage of deploying shards across multiple data centers?

Ensuring availability during regional outages Signup and view all the answers

What is the primary goal of monitoring database migration processes?

To detect anomalies and roll back if necessary Signup and view all the answers

How does Facebook's TAO system route queries across data centers and aggregate results?

TAO, a geographically distributed data store, directs parts of the query to the appropriate shards and aggregates results. Signup and view all the answers

What is the purpose of pre-aggregation in reducing cross-shard queries?

Pre-aggregation pre-computes and stores aggregates to reduce the need for real-time cross-shard queries. Signup and view all the answers

How does MongoDB support sharding?

MongoDB offers built-in support for sharding with automated data distribution and balancing. Signup and view all the answers

How does CockroachDB handle sharding and replication?

CockroachDB is a distributed SQL database that automatically shards and replicates data across nodes. Signup and view all the answers

What is the purpose of Vitess in sharding for MySQL databases?

Vitess is an open-source sharding middleware for MySQL, providing scaling and sharding capabilities for large databases. Signup and view all the answers

How does Apache HBase support sharding?

Apache HBase supports sharding through region servers and automatic splitting. Signup and view all the answers

What is the purpose of Gizzard in sharding?

Gizzard is a sharding framework that provides APIs for managing data distribution and routing across shards. Signup and view all the answers

What is the advantage of using a composite shard key in sharding?

A composite shard key combines multiple attributes, optimizing data distribution based on multiple factors. Signup and view all the answers

What is the purpose of dynamic sharding in a FinTech application?

Dynamic sharding monitors shard load and adjusts the number of shards based on data volume and traffic patterns. Signup and view all the answers

What is the purpose of a Two-Phase Commit protocol in sharding?

The Two-Phase Commit protocol ensures atomic transactions across shards, with fallbacks for compensating transactions. Signup and view all the answers

Study Notes

Re-sharding Strategies

Proactive re-sharding: anticipate growth and performance issues by periodically evaluating data distribution and redistributing before issues arise (e.g., Facebook)
Reactive re-sharding: trigger re-sharding in response to detected imbalances or performance degradation (e.g., online retail platform on Black Friday)

Zero-Downtime Re-sharding Strategies

Dual-writes: temporarily write to both old and new shard configurations while reading from the old until migration is complete (e.g., Twitter)
Phase-based approach: migrate in phases (e.g., start with less critical data) to reduce risk and ensure stability
Blue-green deployments: maintain two parallel environments (old and new shards) to switch traffic seamlessly after the new configuration is fully tested (e.g., Netflix)

Zero-Downtime Migrations

Incremental data copying: gradually copy data from old shards to new ones in small batches to minimize impact (e.g., LinkedIn)
Consistency checks: continuously validate data consistency between old and new shards during migration (e.g., Amazon)
Versioning: implement schema versioning to handle changes without breaking existing queries (e.g., Google Cloud Spanner)
Operational best practices:
- Monitoring and rollback plans: continuously monitor migration process and have rollback procedures in place for quick recovery if issues arise (e.g., Uber)
- Staged migrations: conduct migrations during low-traffic periods and in stages to mitigate risk (e.g., eBay)

Managing Distributed Transactions

Two-Phase Commit (2PC) protocol:
- Ensure atomicity by dividing transaction into two phases: prepare and commit
- Phase 1: each node votes to commit or abort the transaction
- Phase 2: if all nodes vote to commit, transaction is committed; otherwise, it is aborted (e.g., financial institutions)
Challenges with 2PC:
- Blocking nature: participants may be blocked waiting for a response, impacting system performance
- Coordinator failure: failure of the transaction coordinator can lead to uncertainty
Alternative approaches:
- Three-Phase Commit (3PC): adds an extra phase to 2PC to mitigate the blocking problem, but increases complexity and latency (e.g., large-scale retail companies)
- Eventual consistency models: use compensating transactions to resolve inconsistencies over time, suitable for less critical operations (e.g., social media platforms)

Ensuring High Availability

Replication strategies:
- Synchronous replication: ensures immediate consistency by waiting for all replicas to acknowledge writes, but may introduce latency (e.g., banking systems)
- Asynchronous replication: provides higher performance by not waiting for all replicas, at the cost of potential temporary inconsistencies (e.g., e-commerce websites)
Redundancy and failover mechanisms:
- Primary-replica configuration: designate one primary shard for writes and multiple replicas for reads, with automated failover to a replica if the primary fails (e.g., Amazon DynamoDB)
- Multi-data center deployment: deploy shards across multiple data centers to ensure availability during regional outages (e.g., Google Cloud Spanner)

Dealing with Cross-Shard Queries

Challenges with cross-shard queries:
- Complexity: queries involving multiple shards are more complex to design and optimize
- Latency: increased latency due to data being fetched from multiple sources
Techniques to optimize cross-shard queries:
- Distributed SQL engines: use distributed SQL query engines (e.g., Apache Calcite, Google F1) to optimize and execute queries across shards
- Query routing: implement query routers to direct parts of the query to the appropriate shards and aggregate results (e.g., Facebook)
- Pre-aggregation: pre-compute and store aggregates to reduce the need for cross-shard queries in real-time (e.g., Twitter)

Modern Technologies and Frameworks

Sharding support in modern databases:
- MongoDB: offers built-in support for sharding with automated data distribution and balancing (e.g., Craigslist)
- Cassandra: uses partition keys to distribute data across nodes in a cluster, supporting large-scale sharding (e.g., Netflix)
- CockroachDB: a distributed SQL database that automatically shards and replicates data across nodes (e.g., DoorDash)
Frameworks and tools:
- Vitess: an open-source sharding middleware for MySQL, providing scaling and sharding capabilities for large databases (e.g., YouTube)
- Apache HBase: a distributed database that supports sharding through region servers and automatic splitting (e.g., Pinterest)
- Gizzard: a sharding framework that provides APIs for managing data distribution and routing across shards (e.g., Twitter)

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.