What is a centralized lookup service?

Most distributed systemsNetwork of systems each involved in the organization and storage of a large amount of data. fragment into different nodes/servers that contain different records of large data entities.

However, one node is designated as a master nodeThe privileged node maintaining the servers' metadata such that it maintains an updated hash record of what keys are assigned to each of the further servers of the distributed system.

Note: The unique identifier key is used by applications for obtaining further information associated with the relevant key. The application server contacts the master node in such hierarchies.

Operative sequence

The list of sequential steps involved in distributed system lookup are highlighted below:

1. Primarily, the application server sends a request to the master node defining that it needs relevant data associated with the key.

2. The master node uses its updated hash table to map out what server the key would map onto and informs the application server of the relevant server.

3. The application server then contacts the appropriate server directly and requests information corresponding to the key.

4. The server runs a lookup through its storage, fetches the information, and transmits it back to the application server.

Advantages

• Simple to implement: It is convenient to simply assign a singular master node to be the sole entity that should be responsibly maintained without much coordination between the servers themselves.

• Easily scalable: For a growing system, it is fairly straightforward to add more servers for data storage while adding the relevant entries to the hash table in the master node.

Drawbacks

• Exponentially growing hash-table sizes: Growing data complexity would mean that keys need to be rehashed very often, and this would require a repeated revamping of servers.

• Time-consuming: It might sometimes introduce latency as the application server has to await a response regarding server identity and then query the appropriate server.