1. Distributed DBMSs

Parallel DBMSs:

• Nodes are physically close to each other.
• Nodes connected with high-speed LAN.
• Communication cost is assumed to be small.

Distributed DBMSs:

• Nodes can be far from each other.
• Nodes connected using public network.
• Communication cost and problems cannot be ignored.

2. System Architectures

Specifying what shared resources are directly accessible to CPUs.

This affects how CPUs coordinate with each other and where they retrieve/store objects in the database.

2.1 Shared Memory

Same OS instance

CPUs have access to common memory address space via a fast interconnect.

• Each processor has a global view of all the in-memory data structures.
• Each DBMS instance on a processor has to "know" about the other instances.

2.2 Shared Disk

Nodes have their own buffer pool and are considered stateless.

A node crash does not affect the state of the database since that is stored separately on the shared disk.

The storage layer persists the state in the case of crashes.

All CPUs can access a single logical disk directly via an interconnect, but each have their own private memories.

• Can scale execution layer independently from the storage layer.
• Must send messages between CPUs to learn about their current state.

2.3 Shared Nothing