System Design - Scalability: Sharding Part 1

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Questions and Answers

What is sharding, and how does it relate to horizontal partitioning?

Sharding is a form of horizontal partitioning, where rows of a table are distributed across multiple databases.

What is the primary goal of ongoing monitoring and maintenance in a sharded database?

To balance load and ensure optimal performance.

What is the purpose of choosing a shard key in a sharded database?

To select a column that evenly distributes the load.

What is the role of a hash function in hash-based sharding?

To determine the shard based on the user_id. Signup and view all the answers

What is the purpose of implementing shard mapping in a sharded database?

To route queries to the appropriate shard based on the hashed user_id. Signup and view all the answers

How is data insertion handled in a sharded database?

By hashing the user_id to find the target shard and inserting the data. Signup and view all the answers

What is a major challenge in re-sharding data when a shard becomes too large or too small?

It is difficult and resource-intensive. Signup and view all the answers

What is the purpose of the shard key, and why is it crucial to choose the right one?

The shard key is a specific column or set of columns used to determine the distribution of data across shards, and choosing the right shard key is crucial for balancing the load and avoiding hotspots. Signup and view all the answers

What are the three common strategies for shard mapping, and how do they work?

The three common strategies for shard mapping are hash-based sharding, range-based sharding, and directory-based sharding. Signup and view all the answers

What is the purpose of data distribution strategies in sharding, and how do they ensure load balancing?

Data distribution strategies, such as hash-based sharding and range-based sharding, ensure that data is distributed evenly across shards, preventing any single shard from becoming a bottleneck. Signup and view all the answers

What is the importance of replication in sharding, and how does it enhance fault tolerance?

Replication in sharding enhances fault tolerance by ensuring that each shard can be replicated to multiple nodes, making the system more resilient to failures. Signup and view all the answers

What are the benefits of sharding in terms of performance, scalability, and availability?

Sharding improves performance by distributing the load across multiple servers, allows for horizontal scaling, and enhances availability and fault tolerance by isolating failures to individual shards. Signup and view all the answers

What are the challenges of sharding in terms of complexity, data consistency, and query routing?

Sharding adds complexity to database management, requires sophisticated mechanisms for data consistency, and can be challenging for query routing. Signup and view all the answers

How does sharding address the problem of single point of failure, and what are the implications for system availability?

Sharding isolates failures to individual shards, preventing a single point of failure and enhancing overall system availability. Signup and view all the answers

Study Notes

Core Concepts of Sharding

Sharding is a form of horizontal partitioning, where rows of a table are distributed across multiple databases.
A shard key is a specific column or set of columns used to determine the distribution of data across shards.
Shard mapping involves mapping data to specific shards based on the shard key, using strategies such as hash-based, range-based, and directory-based sharding.

Data Distribution Strategies

Hash-Based Sharding: uses a hash function on the shard key to distribute data evenly across shards.
Range-Based Sharding: divides data into contiguous ranges based on the shard key.
Directory-Based Sharding: uses a lookup table to map each shard key to a specific shard.

Load Balancing and Fault Tolerance

Load balancing ensures that each shard holds a balanced amount of data to prevent any single shard from becoming a bottleneck.
Sharding should be combined with replication to enhance fault tolerance, where each shard can be replicated to multiple nodes to ensure high availability.

Benefits of Sharding

Improved Performance: distributes the load across multiple servers, reducing the burden on any single database and improving read and write performance.
Scalability: allows the database to handle increased load by adding more shards, thus enabling horizontal scaling.
Availability and Fault Tolerance: isolates failures to individual shards, preventing a single point of failure and enhancing overall system availability.

Challenges of Sharding

Complexity: adds complexity to database management, requiring sophisticated mechanisms for shard key selection, data distribution, and query routing.
Data Consistency: ensuring consistency across shards can be challenging, especially for cross-shard transactions.
Re-sharding: re-distributing data when a shard becomes too large or too small can be difficult and resource-intensive.
Maintenance: requires ongoing monitoring and maintenance to balance load and ensure optimal performance.

Example of Sharding in Practice

Sharding can be used to distribute user data across multiple databases in a social media platform, improving performance and scalability.
A step-by-step implementation of sharding involves choosing a shard key, determining the sharding strategy, configuring shards, implementing shard mapping, inserting data, and retrieving data.

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