NoSQL papers: All content tagged as NoSQL papers in NoSQL databases and polyglot persistence
A paper by Alexander Shraer, Benjamin Reed, Flavio Junqueira (Yahoo) and Dahlia Malkhi (Microsoft):
Dynamically changing (reconfiguring) the membership of a replicated distributed system while preserving data consistency and system availability is a challenging problem. In this paper, we show that reconfiguration can be simplified by taking advantage of certain properties commonly provided by Primary/Backup systems. We describe a new reconfiguration protocol, recently implemented in Apache Zookeeper. It fully automates configuration changes and minimizes any interruption in service to clients while maintaining data consistency. By leveraging the properties already provided by Zookeeper our protocol is considerably simpler than state of the art.
The corresponding ZooKeeper issue has been created in 2008 and the new protocol should be part of ZooKeeper 3.5.0
Doug Laney left a comment to my Big Data Causes Concern and Big Confusion. A Big Data Definition to Help Clarify the Confusion article pointing to the original 3 V’s paper published in 2001 by META Group1:
While enterprises struggle to consolidate systems and collapse redundant databases to enable greater operational, analytical, and collaborative consistencies, chang- ing economic conditions have made this job more difficult. E-commerce, in particular, has exploded data management challenges along three dimensions: volumes, velocity, and variety. In 2001/02, IT organizations must compile various approaches to have at their disposal for dealing with each.
Give Caesar’s what is Caesar’s. Read or download the paper after the break.
The abstract of a new paper from a team at LinkedIn (Roshan Sumbaly, Jay Kreps, Lei Gao, Alex Feinberg, Chinmay Soman, Sam Shah):
Current serving systems lack the ability to bulk load massive immutable data sets without affecting serving performance. The performance degradation is largely due to index creation and modification as CPU and memory resources are shared with request serving. We have ex- tended Project Voldemort, a general-purpose distributed storage and serving system inspired by Amazon’s Dy- namo, to support bulk loading terabytes of read-only data. This extension constructs the index offline, by leveraging the fault tolerance and parallelism of Hadoop. Compared to MySQL, our compact storage format and data deploy- ment pipeline scales to twice the request throughput while maintaining sub 5 ms median latency. At LinkedIn, the largest professional social network, this system has been running in production for more than 2 years and serves many of the data-intensive social features on the site.
Read or download the paper after the break.
This recent paper from a team at Google is presenting details about Tenzing a system that is currently in use at Google:
Tenzing is a query engine built on top of MapReduce for ad hoc analysis of Google data. Tenzing supports a mostly complete SQL implementation (with several extensions) combined with several key characteristics such as heterogeneity, high performance, scalability, reliability, metadata awareness, low latency, support for columnar storage and structured data, and easy extensibility.
A couple of things I’ve highlighted when reading it:
- Tenzing is in production, but doesn’t serve yet a huge amount of queries
- the backend storage can be a mix of various data stores, such as ColumnIO, Bigtable, GFS files, MySQL databases
- when compared with other similar solutions (Sawzall, Flume-Java, Pig, Hive„ HadoopDB), Tenzing’s advantage is low latency
- the paper acknowledges AsterData, GreenPlum, Paraccel, Vertica for using a MapReduce execution model in their engines
- to perform query optimizations, Tenzing is enhancing queries with information from a metadata server
- there is no information about what kind of metadata is needed in Tenzing. I assume it might refer to details about the data sources and data source metadata (indexes, access patterns, etc)
- to reduce query latency, processes are kept running
- Tenzing supports almost all SQL92 standard and some extensions from SQL99
- projection and filtering (for some of these and depending on the data source Tenzing can do some optimizations)
- set operations (implemented in the reduce phase)
- nested queries and subqueries
- aggregation and statistical functions
- analytic functions (syntax similar to PostgreSQL/Oracle)
- OLAP extensions
Tenzing supports efficient joins across data sources, such as ColumnIO to Bigtable; inner, left, right, cross, and full outer joins; and equi semi-equi, non-equi and function based joins. Cross joins are only supported for tables small enough to fit in memory, and right outer joins are supported only with sort/merge joins. Non-equi correlated subqueries are currently not supported. We include distributed implementations for nested loop, sort/merge and hash joins.
Read and download the “Tenzing A SQL Implementation on the MapReduce framework” after the break.
From the “Temporal Analytics on Big Data for Web Advertising” paper:
TiMR is a framework that transparently combines a map-reduce (M-R) system with a temporal DSMS1. Users express time-oriented analytics using a temporal (DSMS) query lan- guage such as StreamSQL or LINQ. Streaming queries are declarative and easy to write/debug, real-time-ready, and often several orders of magnitude smaller than equivalent custom code for time-oriented applications. TiMR allows the temporal queries to transparently scale on offline temporal data in a cluster by leveraging existing M-R infrastructure.
Broadly speaking, TiMR’s architecture of compiling higher level queries into M-R stages is similar to that of Pig/SCOPE. However, TiMR specializes in time-oriented queries and data, with several new features such as: (1) the use of an unmodified DSMS as part of compilation, parallelization, and execution; and (2) the exploitation of new temporal parallelization opportunities unique to our setting. In addition, we leverage the temporal algebra underlying the DSMS in order to guarantee repeatability across runs in TiMR within M-R (when handling failures), as well as over live data.
According to the paper, DSMS work well for real-time data, but are not massively scalable. On the other hand, Map-Reduce is extremely scalable, but computation is performed on offline data. TiMR proposes a solution that is getting closer to a real-time map-reduce.
Read or download the paper after the break.
This problem has been approached in a few different ways until now. Google’s graph processing framework Pregel, which has some major differences compared to MapReduce, is one of them. There are also some MapReduce implementations for graph processing. Last, but not least different approaches are being tried for scaling graph databases.
Jimmy Lin and Michael Schatz have published in 2010 a paper on the subject of Design patterns for efficient graph algorithms in MapReduce (pdf):
Graphs are analyzed in many important contexts, including ranking search results based on the hyperlink structure of the world wide web, module detection of protein-protein interaction networks, and privacy analysis of social networks. Many graphs of interest are difficult to analyze because of their large size, often spanning millions of vertices and billions of edges. As such, researchers have increasingly turned to distributed solutions. In particular, MapReduce has emerged as an enabling technology for large-scale graph processing. However, existing best practices for MapReduce graph algorithms have significant shortcomings that limit performance, especially with respect to partitioning, serial- izing, and distributing the graph. In this paper, we present three design patterns that address these issues and can be used to accelerate a large class of graph algorithms based on message passing, exemplified by PageRank. Experiments show that the application of our design patterns reduces the running time of PageRank on a web graph with 1.4 billion edges by 69%.
After the break you can find a video of Jimmy Lin talking about current best practices in designing large-scale graph algorithms in MapReduce and how to avoid some of the shortcomings, especially those related to partitioning, serializing, and distributing the graph. He shows three enhanced design patterns applicable to large class of graph algorithms that address many of these deﬁciencies.
A paper from the Seattle University of Washington (Yingyi Bu, Bill Howe, Magdalena Balazinska, Michael D. Ernst):
The growing demand for large-scale data mining and data analysis applications has led both industry and academia to design new types of highly scalable data-intensive computing platforms. MapReduce and Dryad are two popular platforms in which the dataflow takes the form of a directed acyclic graph of operators. These platforms lack built-in support for iterative programs, which arise naturally in many applications including data mining, web ranking, graph analysis, model fitting, and so on. This paper presents HaLoop, a modified version of the Hadoop MapReduce framework that is designed to serve these applications. HaLoop not only extends MapReduce with programming support for iterative applications, it also dramatically improves their efficiency by making the task scheduler loop-aware and by adding various caching mechanisms. We evaluated HaLoop on real queries and real datasets. Compared with Hadoop, on average, HaLoop reduces query runtimes by 1.85, and shuffles only 4% of the data between mappers and reducers.
The embedded paper and download link after the break