Deadly default values in PostgreSQL

While default values in PostgreSQL can be convenient and provide initial values for columns, certain default values can have a detrimental impact on PostgreSQL performance. Here are some examples of potentially deadly default values and their impact:

  1. Default Values that Trigger Expensive Calculations: Setting default values that require complex calculations or extensive data processing can significantly impact performance. Whenever a new row is inserted, the costly calculations are executed, resulting in slower insert operations.
  2. Default Values that Trigger Expensive External Calls: If a default value requires external calls or accesses external resources, such as web services or remote databases, it can introduce delays and potential network issues. This can severely impact the performance of insert or update operations.
  3. Default Values that Trigger Cascade Updates or Deletes: If a default value is set in a column that is part of a foreign key relationship, it can trigger cascading updates or deletes, resulting in expensive operations and potential locking or blocking issues. This can impact both write and read performance.
  4. Default Values that Cause Index Bloat: Setting default values that are not representative of the actual data distribution can lead to index bloat. For example, if a default value is rarely used in queries but is included in an indexed column, it can unnecessarily increase the size of the index, resulting in slower index scans and degraded performance.
  5. Default Values that Cause Data Type Mismatch: Choosing default values that do not match the actual data type of the column can lead to implicit conversions and additional processing overhead. This can result in slower query execution and potential data quality issues.

To avoid these performance pitfalls, it’s essential to carefully consider the default values assigned to columns and their potential impact. Default values should be chosen based on the expected data distribution, query patterns, and the desired performance characteristics of the database system. Regular review and adjustment of default values based on actual usage patterns can help ensure optimal performance and prevent performance bottlenecks.

In conclusion, default values in PostgreSQL can impact performance if they trigger expensive calculations, external calls, cascade updates or deletes, index bloat, or data type mismatch. Careful consideration and testing are necessary when selecting default values to mitigate any adverse impact on PostgreSQL performance.

About Shiv Iyer 219 Articles
Open Source Database Systems Engineer with a deep understanding of Optimizer Internals, Performance Engineering, Scalability and Data SRE. Shiv currently is the Founder, Investor, Board Member and CEO of multiple Database Systems Infrastructure Operations companies in the Transaction Processing Computing and ColumnStores ecosystem. He is also a frequent speaker in open source software conferences globally.