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On Oracle NoSQL Database -Interview with Dave Segleau
On October 3, 2011 Oracle announced the Oracle NoSQL Database, and on December 17, 2012, Oracle shipped Oracle NoSQL Database R2. I wanted to know more about the status of the Oracle NoSQL Database. I have interviewed Dave Segleau, Director of Product Management,Oracle NoSQL Database.
Q1. Who is currently using Oracle NoSQL Database, and for what kind of domain specific applications? Please give us some examples.
Dave Segleau: There are a range of users from segments such as Web-scale Transaction Processing, to Web-scale Personalization and Real-time Event Processing. To pick the area where I would say we see the largest adoption, it would be the Real-time Event Processing category. This is basically the use case that covers things like Fraud Detection, Telecom Services Billing, Online Gaming and Mobile Device Management.
Q2. What is new in Oracle NoSQL Database R2?
Dave Segleau: We added significant enhancements to NoSQL Database in the areas of Configuration Management/Monitoring (CM/M), APIs and Application Developer Usability, as well as Integration with the Oracle technology stack.
In the area of CM/M, we added "Smart Topology" ( an automated capacity and reliability-aware data storage allocation with intelligent request routing), configuration elasticity and rebalancing, JMX/SNMP support. In the area of APIs and Application Developer Usability we added a C API, support for values as JSON objects (with AVRO serialization), JSON schema definitions, and a Large Object API (including a highly efficient streaming interface). In the area of Integration we added support for accessing NoSQL Database data via Oracle External Tables (using SQL in the Oracle Database), RDF Graph support in NoSQL Database, Oracle Coherence as well as integration with Oracle Event Processing.
Q3. How would you compare Oracle NoSQL with respect to other NoSQL data stores, such as CouchDB, MongoDB, Cassandra and Riak?
Dave Segleau: The Oracle NoSQL Database is a key-value store, although it also supports JSON as a value type similar to a document store. Architecturally it is closer to Riak, Cassandra and the Amazon Dynamo-based implementations, rather than the other technologies, at least at the highest level of abstraction. With regards to features, Oracle NoSQL Database shares a lot of commonality with Riak. Our performance and scalability characteristics are showing up with the best results in YCSB benchmarks.
Q4. What is the implication of having Oracle Berkeley DB Java Edition as the core engine for the Oracle NoSQL database?
Dave Segleau: It means that Oracle NoSQL Database provides a mission-critical proven database technology at the heart of the implementation. Many of the other NoSQL databases use relatively new implementations for data storage and replication. Databases in general, and especially distributed parallel databases, are hard to implement well and achieve high product quality and reliability. So we see the use of Oracle Berkeley DB, a pervasively deployed database engine for 1000′s of mission-critical applications, as a big differentiation. Plus, many of the early NoSQL technologies are based on Oracle Berkeley DB, for example LinkedIn's Voldemort, Amazon's Dynamo and other popular commercial and enterprise social media products like Yammer.
The bottom line is that we went down the path of building Oracle NoSQL database because of explicit request from some of our largest Oracle Berkeley DB installations that wanted to move away from maintaining home grown sharding implementations and very much wanted an out of box technology that can replicate the robustness of what they had built "out of box".
Q5. What is the relationships between the underlying "cleaning" mechanism to free up unused space in Oracle Berkeley DB, and the predictability and throughput in Oracle NoSQL Database?
Dave Segleau: As mentioned in the previous section, Oracle NoSQL Database uses Oracle Berkeley DB Java Edition as the key-value storage mechanism within the Storage Nodes. Oracle Berkeley DB Java Edition uses a no-overwrite log file system to store the data and a configurable multi-threaded background log cleaner task to compact and clean log files and free up unused disk space. The Oracle Berkeley DB log cleaner has underdone many years of in-house and real world high volume validation and tuning. Oracle NoSQL Database pre-defines the BDB cleaner parameters for optimal configuration for this particular use case. The cleaner enhances system throughput and predictability by a) running as a low level background task, b) being preconfigured to minimize impact on the running system. The combination of these two characteristics leads to more predictable system throughput.
Several other NoSQL database products have implemented heavy weight tasks to compact, compress and free up disk space. Running them definitely impacts system throughput and predictability. From our point of view, not only do you want a NoSQL database that has excellent performance, but you also need predictable performance. Routine tasks like Java GCs and disk space management should not cause major impacts to operational throughput in a production system.
Q7. Oracle NoSQL data model is using the concepts of "major" and "minor" key path. Why?
Dave Segleau: We heard from customers that they wanted both even distribution of data as well as co-location of certain sets of records. The Major/Minor key paradigm provides the best of both worlds. The Major key is the basis for the hash function which causes Major key values to be evenly distributed throughput the key-value data store. The Minor key allows us to cluster multiple records for a given Major key together in the same storage location. In addition to being very flexible, it also provided additional benefits:
a) A scalable two-tier indexing structure. A hash map of Major Keys to partitions that contain the data, and then a B-tree within each partition to quickly locate Minor key values.
b) Minor keys allow us to perform efficient lookups and range scans within a Major key. For example, for userID 1234 (Major key), fetch all of the products that they browsed from January 1st to January 15th (Minor key).
c) Because all of the Minor key records for a given Major key are co-located on the same storage location, this becomes our basic unit of ACID transactions, allowing applications to have a transaction that spans a single record, multiple records or even multiple write operations on multiple records for a given major key.
This degree of flexibility is often lacking in other NoSQL database offerings.
Q8. Oracle NoSQL database is a distributed, replicated key-value store using a shared-nothing master-slave architecture. Why did you choose to have a master node architecture? How does it compare with other systems which have no master?
Dave Segleau: First of all, lets clarify that each shard has a master (multi master) and it is an elected master based system. The Oracle NoSQL Database topology is deployed with user-specified replication factor (how many copies of the data should the system maintain) and then using a PAXOS based mechanism, a master is elected. It is quite possible that a new master is elected under certain operating conditions. Plus, if you throw more hardware resources at the system, those "masters" will shift the data for which they are responsible, again to achieve the optimal latency profile. We are leveraging the enterprise grade replication technology that is widely deployed via the Oracle Berkeley DB Java Edition. Also, by using an elected master implementation, we can provide a fully ACID transaction on an operation by operation basis
Q9. It is known that when the master node for a particular key-value fails (or because of a network failure), some writes may get lost. What is the implication from an application point of view?
Dave Segleau: This is a complex question in that it depends largely on the type of durability requested for the operation and that is controlled by the developer. In general though, committed transactions acknowledged by a simple majority of nodes (our default durability) are not lost when a master fails. In the case of less aggressive durability policies, in-flight transactions that have been subject to network, disk, server failures, are handled similar to process failure in other database implementations, the transactions are rolled back. However, a new master will quickly be elected and future requests will go thru without a hitch. The applications can guard against such situations by handling exceptions and performing a retry.
Q10. Justin Sheehy of Basho in an interview said (1): "I would most certainly include updates to my bank account as applications for which eventual consistency is a good design choice. In fact, bankers have understood and used eventual consistency for far longer than there have been computers in the modern sense" Would you recommend to your clients to use Oracle NoSQL database for banking applications?
Dave Segleau: Absolutely. The Oracle NoSQL Database offers a range of transaction durability and consistency options on a per operation basis. The choice of eventual consistency is best made on a case by case basis, because while using it can open up new levels of scalability and performance, it does come with some risk and/or alternate processes which have a cost. Some NoSQL vendors don't provide the options to leverage ACID transactions where they make sense, but the Oracle NoSQL Database does.
Q11. Could you detail how Elasticity is provided in R2?
Dave Segleau: The Oracle NoSQL database slices data up into partitions within highly available replication groups. Each replication group contains an elected master and a number of replicas based on user configuration. The exact configuration will vary depending on the read latency /write throughput requirements of the application. The processes associated with those replication groups run on hardware (Storage Nodes) declared to the Oracle NoSQL Database. For elasticity purposes, additional Storage Nodes can be declaratively added to a running system, in which case some of the data partitions will be re-allocated onto the new hardware, thereby increasing the number of shards and the write throughput. Additionally, the number of replicas can be increased to improved read latency and increase reliability. The process of rebalancing data partitions, spawning new replicas, and forming new Replication Groups will cause those internal data partitions to automatically move around the Storage Nodes to take advantage of the new storage capacity.
Q12. What is the implication from a developer perspective of having a Avro Schema Support?
Dave Segleau: For the developer, it means better support for seamless JSON storage. There are other downstream implications, like compatibility and integration with Hadoop processing where AVRO is quickly becoming a standard not only for efficient wireline serialization protocols, but for HDFS storage. Also, AVRO is a very efficient serialization format for JSON, unlike other serialization options like BSON which tend to be much less efficient. In the future, Oracle NoSQL Database will leverage this flexible AVRO schema definition in order to provide features like table abstractions, projections and secondary index support.
Q13. How do you handle Large Object Support?
Dave Segleau: Oracle NoSQL Database provides a streaming interface for Large Objects. Internally, we break a Large Object up into chunks and use parallel operations to read and write those chunks to/from the database. We do it in an ordered fashion so that you can begin consuming the data stream before all of the contents are returned to the application. This is useful when implementing functionality like scrolling partial results, streaming video, etc. Large Object operations are restartable and recoverable. Let's say that you start to write a 1 GB Large Object and sometime during the write operation a failure occurs and the write is only partially completed. The application will get an exception. When the application re-issues the Large Object operation, NoSQL resumes where it left off, skipping chunks that were already successfully written.
The Large Object chunking implementation also ensures that partially written Large Objects are not readable until they are completely written.
Q14. A NoSQL Database can act as an Oracle Database External Table. What does it mean in practice?
Dave Segleau: What we have achieved here is the ability to treat the Oracle NoSQL Database as a resource that can participate in SQL queries originating from an Oracle Database via standard SQL query facilities. Of course, the developer has to define a template that maps the "value" into a table representation. In release 2 we provide sample templates and configuration files that the application developer can use in order to define the required components. In the future, Oracle NoSQL Database will automate template definitions for JSON values. External Table capabilities give seamless access to both structured relational and unstructured NoSQL data using familiar SQL tools.
Q15. Why Atomic Batching is important?
Dave Segleau: If by Atomic Batching you mean the ability to perform more than one data manipulation in a single transaction, then atomic batching is the only real way to ensure logical consistency in multi-data update transactions. The Oracle NoSQL Database provides this capability for data beneath a given major key.
Q16 What are the suggested criteria for users when they need to choose between durability for lower latency, higher throughput and write availability?
Dave Segleau: That's a tough one to answer, since it is so case by case dependent. As discussed above in the banking question, in general if you can achieve your application latency goals while specifying high durability, then that's your best course of action. However, if you have more aggressive low-latency/high-throughput requirements, you may have to assess the impact of relaxing your durability constraints and of the rare case where a write operation may fail. It's useful to keep in mind that a write failure is a rare event because of the inherent reliability built into the technology.
Q17. Tomas Ulin mentioned in an interview (2) that "with MySQL 5.6, developers can now commingle the "best of both worlds" with fast key-value look up operations and complex SQL queries to meet user and application specific requirements". Isn't MySQL 5.6 in fact competing with Oracle NoSQL database?
Dave Segleau: MySQL is an SQL database with a KV API on top. We are a KV database. If you have an SQL application with occasional need for fast KV access, MySQL is your best option. If you need pure KV access with unlimited scalability, then NoSQL DB is your best option.
David Segleau is the Director Product Management for the Oracle NoSQL Database, Oracle Berkeley DB and Oracle Database Mobile Server. He joined Oracle as the VP of Engineering for Sleepycat Software (makers of Berkeley DB). He has more than 30 years of industry experience, leading and managing technical product teams and working extensively with database technology as both a customer and a vendor.
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