Nosql Questions Long
In NoSQL databases, there are different transaction models used to ensure data consistency and integrity. These models vary from traditional ACID (Atomicity, Consistency, Isolation, Durability) transactions used in relational databases. The different transaction models used in NoSQL databases are as follows:
1. BASE (Basically Available, Soft state, Eventually consistent): This model focuses on providing high availability and scalability by relaxing the consistency guarantees. It allows for eventual consistency, where data may be inconsistent for a short period but will eventually converge to a consistent state. BASE transactions are often used in distributed systems to handle large-scale data processing.
2. Eventual Consistency: This model guarantees that if no updates are made to a data item, eventually all accesses to that item will return the last updated value. It allows for concurrent updates and replication across multiple nodes, but there may be a delay in propagating updates, leading to temporary inconsistencies.
3. Optimistic Concurrency Control: This model allows multiple transactions to proceed concurrently without locking the data. Each transaction is assigned a timestamp, and conflicts are resolved during the commit phase. If conflicts occur, the transaction is rolled back and can be retried.
4. Multi-Version Concurrency Control (MVCC): This model maintains multiple versions of data items to allow concurrent transactions to read and write without blocking each other. Each transaction sees a consistent snapshot of the database at the start of the transaction, and changes made by other transactions are isolated.
5. Distributed Transactions: This model deals with transactions that span multiple nodes or partitions in a distributed database. It ensures that all operations within a transaction are either committed or rolled back atomically across all participating nodes, maintaining data consistency across the distributed system.
6. Read-Committed Isolation: This model provides a higher level of consistency than eventual consistency. It ensures that a transaction only reads committed data, preventing dirty reads and non-repeatable reads. However, it does not guarantee serializability or isolation from concurrent writes.
It's important to note that not all NoSQL databases support all of these transaction models. The choice of transaction model depends on the specific requirements of the application and the trade-offs between consistency, availability, and scalability.