Why do open source databases like MongoDB and PostgreSQL depend on shared memory for performance?

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Open-source databases like MongoDB and PostgreSQL rely heavily on shared memory to optimize performance because shared memory allows efficient inter-process communication and data sharing without the overhead of disk I/O or redundant data copies. Here’s a breakdown of why shared memory is critical:

🧠 What Is Shared Memory?

Shared memory is a memory segment that multiple processes can access simultaneously. In databases, it enables components like client processes, background workers, and cache systems to read and write data concurrently without duplicating memory.

🚀 Why Shared Memory Boosts Database Performance

1. Efficient Buffer Caching

• PostgreSQL and MongoDB use shared memory to hold a buffer pool — an in-memory cache of frequently accessed database pages.
• This avoids costly disk reads by allowing all processes to access a centralized memory area for cached data.

💡 Example: In PostgreSQL, the shared buffer pool is a shared memory segment where disk pages are cached. All backend processes read/write from this area, reducing redundant I/O operations.