How do distributed systems handle concurrent operations?

Distributed systems handle concurrent operations through techniques like locking, optimistic concurrency control, and distributed transactions.

In a distributed system, multiple nodes work together to perform operations concurrently. This can lead to conflicts if not managed properly. One common way to handle concurrent operations is through locking. Locking is a mechanism where a node locks a data item when it wants to perform an operation on it. This prevents other nodes from accessing or modifying the data item until the lock is released. This ensures that operations are performed in a controlled manner, avoiding conflicts and inconsistencies.

Another technique used is optimistic concurrency control (OCC). Unlike locking, OCC allows multiple nodes to access and modify data items concurrently. It operates under the assumption that conflicts are rare. When a node wants to commit its changes, it checks if any other node has modified the data item since it last accessed it. If there has been a modification, the node must discard its changes and start over. This technique is beneficial in scenarios where read operations are more frequent than write operations.

Distributed transactions are another method used to handle concurrent operations. A distributed transaction is a set of operations that are performed across multiple nodes. These operations are treated as a single logical unit, meaning either all operations are successful, or none are. This is known as atomicity. Distributed transactions also ensure consistency, isolation, and durability (ACID properties). Consistency ensures the system remains in a consistent state before and after the transaction. Isolation ensures that each transaction is executed in isolation from other transactions. Durability ensures that once a transaction is committed, it remains so, even in the event of failures.

In addition to these techniques, distributed systems also use replication for handling concurrent operations. Replication involves maintaining multiple copies of the same data item on different nodes. This allows operations to be performed on any copy, increasing availability and performance. However, replication also introduces the challenge of maintaining consistency among the copies. This is typically handled through replication strategies like primary-backup or multi-master replication.

In conclusion, handling concurrent operations in distributed systems is a complex task that involves managing conflicts and ensuring consistency. Various techniques like locking, OCC, distributed transactions, and replication are used to achieve this.