What does CRAQ mean in DATABASES

Chain Replication with Apportioned Queries (CRAQ) is an algorithm for distributed systems that enables multiple replicas of one or more databases to be spread across different nodes in a network. This ensures that the data on the database remain consistent and available at all times, even when individual nodes in the network fail or become unavailable. CRAQ is particularly designed for large-scale databases, where it is important to apportion queries across multiple replicas and ensure that all query results are correct and up to date.

In chain replication, each replica node has the entire database in its store. Data replication takes place as a chain reaction - when a change is made at one node, it replicates outwards to subsequent nodes in the chain. This means that if one node fails or becomes disconnected from the network, the next node along can take over providing the same services without any interruption.

Query apportioning involves spreading out queries between different replicas and ensuring that every replica has an equal number of queries so as to balance out their workloads. This ensures good performance and reliability of data throughout the system while also reducing conflict between queries sent by different users or processes.

By apportioning queries between multiple replicas, CRAQ allows for improved parallelism and scalability since more work can be processed simultaneously without increasing latency or contention between competing requests. Furthermore, since each replica holds a full copy of the database, complex computations such as join operations can be performed more efficiently since no communication between different nodes in required.

Yes - through its use of chained replication and query apportionment, CRAQ ensures that all replicas contain identical information and updates are propagated quickly across all nodes in order to maintain consistent data throughout the system.

If two updates are received at different nodes concurrently but conflict with each other (such as both updating the same record), then CRAQ employs an optimistic concurrency control protocol which resolves conflicts by applying either one update first then discarding any conflicting updates or using logical timestamp ordering to determine which update was received first and should therefore take precedence over any other subsequent modifications.

Yes - if there are too few replicas in operation then additional ones can be added on demand (up to an agreed maximum). Also if too many replicas are running for a particular workload then some can be removed in order to better balance resources within the system.

The use of CRAQ should generally be considered for applications where reads vastly exceed writes; i.e., read-heavy workloads where data availability must remain high regardless of how many users/processes send requests simultaneously or how frequently changes occur on individual records within a given dataset.

No - provided you have available network infrastructure capable of carrying traffic between different nodes (which must generally have some degree of physical proximity) then it should not require any specific hardware configuration beyond what would normally be expected for deployment into production environments.