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http://www.agildata.com/database-sharding/
When Database Sharding is Appropriate
Database Sharding is an excellent fit for many types of business applications, those with general purpose database requirements. It can also be used effectively for Data Warehousing applications, and as there are many available products and technologies to accomplish this, we will not focus on this element here.
The general purpose database requirements that are a fit for sharding include:
- High-transaction database applications
- Mixed workload database usage
- Frequent reads, including complex queries and joins
- Write-intensive transactions (CRUD statements, including INSERT, UPDATE, DELETE)
- Contention for common tables and/or rows
- General Business Reporting
- Typical “repeating segment” report generation
- Some data analysis (mixed with other workloads)
To determine if Database Sharding is applicable to your specific application or environment, the most important thing to evaluate is how well your database schema lends itself to sharding. In essence, Database Sharding is a method of “horizontal” portioning, meaning that database rows (as opposed to columns) for a single schema table are distributed across multiple shards. To understand the characteristics of how well sharding fits a given situation, here are the important things to determine:
- Identify all transaction-intensive tables in your schema.
- Determine the transaction volume your database is currently handling (or is expected to handle).
- Identify all common SQL statements (SELECT, INSERT, UPDATE, DELETE), and the volumes associated with each.
- Develop an understanding of your “table hierarchy” contained in your schema; in other words the main parent-child relationships.
- Determine the “key distribution” for transactions on high-volume tables, to determine if they are evenly spread or are concentrated in narrow ranges.