Sorted String Table is a file of key/value string pairs, sorted by keys. An SSTable can be completely mapped into memory, which allows us to perform lookups and scans without touching disks.An SSTable provides a persistent, ordered an immutable map from keys to values, where both keys and values are arbitrary byte strings. Operations are provided to look up the value associated with a specified key and to iterate over all key/value pairs in a specified key range. SSTable is a simple abstraction to efficiently store large numbers of key-value pairs while optioning for high throughput, sequential read/write workloads. Internally, each SSTable contains a sequence of blocks typically each block is 64KB in size, but this is configurable. A block index stored at the end of the SSTable is used to locate blocks; the index is loaded into memory when the SSTable is opened. The features of SSTable are: SSTables are immutable, simplifies caching, sharing across GFS etc., serializable index, serializable data, bloom filter, no need for concurrency control, SSTables of a tablet recorded in METADATA table, Garbage collection of SSTables done by master, on tablet split, split tables can start off quickly on shared SSTables, splitting them lazily. SSTable works in Cassandra (data format, indexing, serialization, searching).
Published in Chapter:
NoSQL Databases
Mainak Adhikari (IMPS College of Engineering and Technology, India) and Sukhendu Kar (IMPS College of Engineering and Technology, India)
Copyright: © 2015
|Pages: 44
DOI: 10.4018/978-1-4666-6559-0.ch006
Abstract
NoSQL database provides a mechanism for storage and access of data across multiple storage clusters. NoSQL dabases are finding significant and growing industry to meet the huge data storage requirements of Big data, real time applications, and Cloud Computing. NoSQL databases have lots of advantages over the conventional RDBMS features. NoSQL systems are also referred to as “Not only SQL” to emphasize that they may in fact allow Structured language like SQL, and additionally, they allow Semi Structured as well as Unstructured language. A variety of NoSQL databases having different features to deal with exponentially growing data intensive applications are available with open source and proprietary option mostly prompted and used by social networking sites. This chapter discusses some features and challenges of NoSQL databases and some of the popular NoSQL databases with their features on the light of CAP theorem.