This can break scripts that rely on the exact format of the output. For this reason, we encourage programs which consume the output of the commandline client to consider using the --xml option, or accessing Subversion through the various bindings interfaces. Below is an example of the new output:
Main features[ edit ] Distributed Every node in the cluster has the same role. There is no single point of failure. Data is distributed across the cluster so each node contains different databut there is no master as every node can service any request.
Supports replication and multi data center replication Replication strategies are configurable. Scalability Designed to have read and write throughput both increase linearly as new machines are added, with the aim of no downtime or interruption to applications. Fault-tolerant Data is automatically replicated to multiple nodes for fault-tolerance.
Replication across multiple data centers is supported. Failed nodes can be replaced with no downtime. Tunable consistency Cassandra is typically classified as an AP systemmeaning that availability and partition tolerance are generally considered to be more important than consistency in Cassandra Writes and reads offer a tunable level of consistencyall the way from "writes never fail" to "block for all replicas to be readable", with the quorum level in the middle.
There is support also for Apache Pig and Apache Hive. CQL adds an abstraction layer that hides implementation details of this structure and provides native syntaxes for collections and other common encodings.
Known issues[ edit ] Up to Cassandra 1. One update may affect one column while another affects the other, resulting in sets of values within the row that were never specified or intended. Its data model is a partitioned row store with tunable consistency. Rather, Cassandra emphasizes denormalization through features like collections.
Column families contain rows and columns. Each row is uniquely identified by a row key. Each row has multiple columns, each of which has a name, value, and a timestamp. Unlike a table in an RDBMS, different rows in the same column family do not have to share the same set of columns, and a column may be added to one or multiple rows at any time.
Each key has values as columns, and columns are grouped together into sets called column families.
Thus, each key identifies a row of a variable number of elements. These column families could be considered then as tables. A table in Cassandra is a distributed multi dimensional map indexed by a key. Furthermore, applications can specify the sort order of columns within a Super Column or Simple Column family.
The JMX-compliant nodetool utility, for instance, can be used to manage a Cassandra cluster adding nodes to a ring, draining nodes, decommissioning nodes, and so on. This section may contain indiscriminateexcessiveor irrelevant examples.
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The Access Log Valve creates log files in the same format as those created by standard web servers. These logs can later be analyzed by standard log analysis tools to track page hit counts, user session activity, and so on.
This Valve uses self-contained logic to write its log files, which can be automatically rolled over at midnight each day.