But yes, this is a problem on any DB. The moment it hits disk, performance is terrible.
This is an over-simplification for any mature database unless all you care about are massive, completely random read workloads[1]. RAM will obviously be faster but there's a difference between terrible and performing at the level of the underlying disk subsystem. With a decent system, commits per second should track the underlying storage array's IOPS, large read / write traffic should be capable of approaching disk bandwidth, etc.
Where things do get bad is when the database is doing more random I/O than required by the workload – if storage is fragmented, it's playing sim-MySQL and creating lots of temporary tables, etc. you will see performance which is pathologically worse. This is a bug and should be fixed.
1. If writes aren't disk I/O limited, you should expect data loss because it's lying about durability.
Comments
This is an over-simplification for any mature database unless all you care about are massive, completely random read workloads[1]. RAM will obviously be faster but there's a difference between terrible and performing at the level of the underlying disk subsystem. With a decent system, commits per second should track the underlying storage array's IOPS, large read / write traffic should be capable of approaching disk bandwidth, etc.
Where things do get bad is when the database is doing more random I/O than required by the workload – if storage is fragmented, it's playing sim-MySQL and creating lots of temporary tables, etc. you will see performance which is pathologically worse. This is a bug and should be fixed.
1. If writes aren't disk I/O limited, you should expect data loss because it's lying about durability.