Giving PostgreSQL too much memory, particularly with settings like `maintenance_work_mem` and `work_mem`, can degrade performance instead of enhancing it. A common misconception is that higher memory limits always lead to better performance. The author presents an example involving GIN index builds, where increasing `maintenance_work_mem` from 64MB to 16GB extended duration by 30%. Despite using parallel workers, which initially improved speed, too much memory led to slower processing. The author identifies two main reasons for this problem. First, the speed differences between RAM types matter. On-CPU L3 cache is significantly faster than main memory. When data processing exceeds the L3 cache, the system must access slower main memory, increasing overall processing time. Smaller data chunks that fit within the L3 cache can improve efficiency, even if they require more processing steps. Second, larger memory chunks can create pressure on system resources. If the hash table exceeds the memory limit, it writes temporary data to disk. This can trigger synchronous writes, which stall operations, while smaller, more frequent writes allow the kernel to manage data more effectively. The same logic applies to `work_mem`, which affects regular queries. When operations exceed the L3 cache, performance drops. The author suggests using modest settings, such as 64MB, and only increasing them if clear benefits can be demonstrated. Blindly setting high values may backfire, causing more harm than good.