Split-brain (computing)

Split-brain (computing)

Split-brain is a computer term, based on an analogy with the medical Split-brain syndrome. It indicates data or availability inconsistencies originating from the maintenance of two separate data sets with overlap in scope, either because of servers in a network design, or a failure condition based on servers not communicating and synchronizing their data to each other. This last case is also commonly referred to as a network partition. Although the term split-brain typically refers to an error state, Split-brain DNS (or Split-horizon DNS) is sometimes used to describe a deliberate situation where internal and external DNS services for a corporate network are not communicating, so that separate DNS name spaces are to be administered for external computers and for internal ones. This requires a double administration, and if there is domain overlap in the computer names, there is a risk that the same fully qualified domain name (FQDN), may ambiguously occur in both name spaces referring to different computer IP addresses. High-availability clusters usually use a heartbeat private network connection which is used to monitor the health and status of each node in the cluster. For example, the split-brain syndrome may occur when all of the private links go down simultaneously, but the cluster nodes are still running, each one believing they are the only one running. The data sets of each cluster may then randomly serve clients by their own "idiosyncratic" data set updates, without any coordination with the other data sets. This may lead to data corruption or other data inconsistencies that might require operator intervention and cleanup.

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Split releases

A Wild Pear (Split 7" with The Evaporators) (2009, Mint Records, Nardwuar Records) We Got a Groove (Split 7" with Riverboat Gamblers) (2009, Volcom Entertainment)

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Leader of a split party

On 29 October 1941, the police arrested Abdullah Mas'ud and Fahd took over his leadership role. Fahd's leadership style led to a dispute with a prominent member of the leadership, Zhu Nun Ayyub, who repeatedly demanded that Fahd convene a party congress which would adopt rules for the party. Fahd responded by having Ayyub and his supporters expelled in August 1942. In November 1942 Fahd demanded the sacking from the Central Committee of another member, Wadi' Talyah. His opponents on the committee refused to accept this, and accused him of egocentrism and dictatorship. The row had not been resolved when Fahd had to travel abroad. During his absence, Abdullah Mas'ud's supporters called a party congress without informing other members of the Central Committee. The congress, held on 20 November, dismissed all Fahd's supporters - but not Fahd himself - from the committee and elected Mas'ud first secretary. As the new Central Committee had retained control of Al-Sharara, Fahd's supporters started issuing a new journal, entitled al-Qa'ida (the base), in February 1943. Fahd returned to Baghdad in April 1943, and the difficult process of reuniting the party began. However, he was soon able to concentrate on organisational work.

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Almost-split sequences

Suppose that R is an Artin algebra. A sequence 0 A B C 0of finitely generated left modules over R is called an almost-split sequence (or Auslander-Reiten sequence) if it has the following properties: The sequence is not split C is indecomposable and any homomorphism from an indecomposable module to C that is not an isomorphism factors through B. A is indecomposable and any homomorphism from A to an indecomposable module that is not an isomorphism factors through B.For any finitely generated left module C that is indecomposable but not projective there is an almost-split sequence as above, which is unique up to isomorphism. Similarly for any finitely generated left module A that is indecomposable but not injective there is an almost-split sequence as above, which is unique up to isomorphism. The module A in the almost split sequence is isomorphic to D Tr C, the dual of the transpose of C. ExampleSuppose that R is the ring k[x]/(xn) for a field k and an integer n1. The indecomposable modules are isomorphic to one of k[x]/(xm) for 1 m n, and the only projective one has m=n. The almost split sequences are isomorphic to 0 k [ x ] / ( x m ) k [ x ] / ( x m 1 ) k [ x ] / ( x m 1 ) k [ x ] / ( x m ) 0 displaystyle 0

ightarrow k[x]/(x^m)

ightarrow k[x]/(x^m1)oplus k[x]/(x^m-1)

ightarrow k[x]/(x^m)

ightarrow 0 for 1 m