It means that in the following case both executions are equal: f(a,f(b,c)) = f(f(a,b),c).
In the other side we can classify as not monothonic the operations like: variable overwrites or removals from collections.Īnd this CALM theorem encompasses ACID 2.0 that will be explained in the next section. Among the monothonic operations we can distinguish: variables initialization to specific value or data accumulation inside collections. Any monotonic program can be then eventually consistent without any additional coordination points. What does it mean ? A monotonic operation is the operation that adds new data to the input and, in consequence, it can only increase or decrease the output (the output grows in only 1 direction). In the latter case it means that the consistency must be strengthened.Īs you can see, the monotonic is a keyword of CALM. The monotonicity is used here to determine if given programs are safe under eventual consistency or not. It's a theorem relating the monotonic logic to the data consistency in distributed environments. But before we develop these points, let's stop a moment and focus on another acronym being the departure point for ACID 2.0 - CALM.ĬALM means Consistency As Logical Monotonicity.
The latter one is more about flexibility and robustness because it means: Associative, Commutative, Idempotent and Distributed. The first acronym focuses on correctness and precision (for reminder, it means: Atomicity, Consistency, Isolation, Durability). Shortly speaking, the difference between ACID and ACID 2.0 is expressed in the targeted properties. The last section gives an example of its use. Only the next part talks about ACID 2.0 principles. The first part explains the CALM theorem that is strictly related to the ACID 2.0.
#Acid database software
Durability is ensured by using database backups and transaction logs that facilitate the restoration of committed transactions despite any subsequent software or hardware failures.This post focuses on this another ACID-like acronym.
Durability ensures that any transaction committed to the database is not lost.The isolation property does not ensure which transaction executes first-only that transactions will not interfere with each other. This prevents Joe's transaction from reading intermediate data produced as a side effect of part of Mary's transaction that will not eventually be committed to the database. The database should either perform Joe's transaction before executing Mary's or vice-versa. For example, if Joe issues a transaction against a database at the same time that Mary issues a different transaction, both transactions should operate on the database in an isolated manner. Isolation requires that multiple transactions occurring at the same time not impact each other's execution.On the other hand, if a transaction successfully executes, it takes the database from one state that is consistent with the rules to another state that is also consistent with the rules. If a transaction is executed that violates the database's consistency rules, the entire transaction is rolled back, and the database is restored to a state consistent with those rules. Consistency states that only valid data will be written to the database.It is critical that the database management system maintains the atomic nature of transactions in spite of any DBMS, operating system, or hardware failure. If one part of the transaction fails, the entire transaction fails. Atomicity states that database modifications must follow an all-or-nothing rule.
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