Re:What PostgreSQL has over other open source SQL databases:...
by lobster_johnson on Sunday October 25, 2015 @02:16AM
(#10446156)
> HBase is not ACID and therefore not strongly consistent. The consistency in CAP is different than consistency in ACID.
You're arguing the word "consistent" is used wrong, and then you go on to mixing ACID and CAP — two acronyms which use the word "consistent" with completely different meanings.
The "C" in ACID stands for data consistency, which is that you shouldn't be allowed to store any data which isn't internally consistent with the schema's consistency rules. For example, you're not allowed to store a "null" value in a "not null" column, and you can't delete a row that is pointed to by a different table's foreign key constraint.
The "C" in Brewer's original CAP theorem really represents atomic consistency. It's the idea that if you submit data, you should get the exact same data back, even if you ask a different node. It sort of represents both the "A" (atomicity, in the sense that either everything or nothing is updated) in ACID, as well as the "I" (isolation, in the sense that nodes don't see partial writes) and "D" (durability, in the sense that data written stays written).
In CAP terms, HBase is strongly consistent, I believe, as long as you query the primary region server and not a replica. But HBase is not transactional, and therefore it's pretty meaningless to talk about ACID.
You're arguing the word "consistent" is used wrong, and then you go on to mixing ACID and CAP — two acronyms which use the word "consistent" with completely different meanings.
The "C" in ACID stands for data consistency, which is that you shouldn't be allowed to store any data which isn't internally consistent with the schema's consistency rules. For example, you're not allowed to store a "null" value in a "not null" column, and you can't delete a row that is pointed to by a different table's foreign key constraint.
The "C" in Brewer's original CAP theorem really represents atomic consistency. It's the idea that if you submit data, you should get the exact same data back, even if you ask a different node. It sort of represents both the "A" (atomicity, in the sense that either everything or nothing is updated) in ACID, as well as the "I" (isolation, in the sense that nodes don't see partial writes) and "D" (durability, in the sense that data written stays written).
In CAP terms, HBase is strongly consistent, I believe, as long as you query the primary region server and not a replica. But HBase is not transactional, and therefore it's pretty meaningless to talk about ACID.