I’m just reviewing Oracle NoSQL database. This database is part of BigData and Oracle has an interesting view about the coexistence of NoSQL, Hadoop, Traditional SQL.
Check out this image:
Oracle view is really impressive and may become a real challenge.
Oracle claims to have a BASE compliant database but this seems not true. Reading documentation you can discover that sometimes eventual consistency model is not obeyed.
I’m also impressed from this technical aspect: ACID compliant transactions. Is this the first NoSQL database ACID compliant? Is Oracle able to deal against a paradigm? Is it able to change the theory? Of course not.
Support for atomic transactions is not provided in fact and this is in contrast with A of ACID.
Ending, I can suggest the interesting overview offered by Daniel Abadi, available here. Furthermore you may also check this cool link too.
This is a really interesting question. Many people are force to think that MySQL is not totally ACID compliant due to some limitation of MySQL itself or limits introduced by some particular storage engine.
We cannot hide that old versions of MySQL were not aware of the concept to transaction and transaction is a concept must be present in an ACID database. Also ACID implying a good design of application and data, as said by Alex Popescu:
That’s because you are basically taking your data and vomiting it on the hard drive without any consideration as to if your data you are writing is sensible or simply dreamed up by magic pixies.
You may also find an interesting bug opened to MySQL: bug #62209. There is a nice complain about ACID functionalities when MySQL is used with InnoDB. Jordan Hall also made a simple test about the functionalities of CHECK constraints in MySQL showing that ACID is not totally supported.
At the end, this famous video:
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by: gar1t
This concept is almost unknown by people. Googling for Oracle Transaction Isolation Level the first post is a PowerPoint file from the University of Indiana about Oracle Locking mechanisms that is not strictly related and sometime confused with transaction isolation level.
Transaction Isolation Level is a property of ACID model called Isolation and is described here on wikipedia.
Oracle talks about its own isolation level in the Concepts Book, chapter 13. Probably with Oracle you’ve never heard anything about this because:
- You’ve not read carefully the Concepts book
- You don’t know all about ACID model
- You don’t know anything that is not Oracle and it’s normal workig way
- Most developers don’t use Isolation Level (probably because they don’t know it)
It’s important to understand that oracle use the read consistency isolation level and in particular Oracle use if at statement level. Thus you are sure that data for every query comes from a single point. This does not eliminate the possibilty to change isolation level for a particular transaction.
Locking mechanism is important but is not strictly related to isolation level. Locking mechanism prevent destructive interaction between transactions accessing the same resource. Particular attention have to be used when you force isolation level to serialize because the way of locking and possibile locks