Notes Archives - Page 4 of 5

TCP Congestion control algorithm 1

Apr

4

2013

Re-transmissions, Timeouts and Duplicate Acknowledgements TCP is relegated to rely mostly upon implicit signals it learns from the network and remote host. TCP must make an educated guess as to the state of network and trust the information from the remote host in order to control the rate of data flow. A sender’s implicit ...

Spanning Trees

Apr

4

2013

Let G = (V, E) be a connected graph in which each edge (u, v) E has an associated cost C(u, v). A Spanning Tree for G is a subgraph of G that it is a free tree connecting all vertices in V. The cost of a spanning tree is the sum of costs on its edges. Minimum Spanning Tree An MST of G is a spanning tree of G having a minimum cost. ...

Serializability

Apr

4

2013

Basic Assumption – Each transaction preserves database consistency Thus, serial execution of set of transactions preserves database consistency. A (possibly concurrent) schedule is serializable if it os equivalent to serial schedule (say, Transaction T1 follows Transaction T2 or T2 follows T1) Different form of schedule equivalence gives rise to the notions of 1. ...

Recoverable and Cascadeless Schedules 36

Apr

4

2013

Recoverability A recoverable schedule is one where, for each pair of Transaction Ti and Tj such that Tj reads data item previously written by Ti the commit operation of Ti appears before the commit operation Tj . Suppose that the system allows T9 to commit immediately after execution of read(A) instruction.Thus T9 commit before T8 does. Now suppose that T8 fails ...

Normal Forms in Database

Apr

4

2013

INF A relation is in first normal form if the domain of each attributes contains only atomic values and value of each attribute contains only a single value from that hand. #Eliminate duplicative columns from the same table #Create separate table for each group of related data and identify each row with unique column(primary ...

Kernel mode and User mode

Apr

4

2013

Kernel mode In the kernel mode, the executing code has complete and unrestricted access to the underlying hardware. It can execute any CPU instruction and reference any memory address.Kernel mode is generally reserved for the lowest level, most trusted function of operating system. User mode In user mode, the executing code has no ability ...

Interrupts

Apr

4

2013

An interrupt is a signal to the processor emitted by hardware or software indicating an occurrence of an event that needs immediate attention.The processor responds by suspending its current activities, saving its state, and executing a small program called an interrupt handler (or interrupt service routine, ISR) to deal with the event. This interruption is temporary, and after ...

Floyd’s Algorithm for shortest path

Apr

4

2013

Based on Dynamic Programming It is a graph analysis algorithm for finding shortest paths in a weighted graph with positive or negative edge(but without negative cycle)(shortest path between all pairs) The single execution of the algorithm will find the lengths(summed weights) of the shortest paths between all pairs of vertices. though it does not ...

C Calling convention and stack

Apr

3

2013

The formal arguments and local variables are defined inside a function are created at a place in memory called ‘stack’.When the control returns from the function the stack is cleaned up either by the ‘Calling function’ or by the ‘Called function’, which would do this is decided by the calling convention. Standard calling convention in ...

Timestamp Based Protocol 1

Apr

1

2013

Timestamps With each transaction Ti in the system, we associate a unique fixed timestamp, denoted by TS (Ti ). This timestamp is assigned by the database system before the Transaction Ti starts execution. If a transaction Ti has been assigned timestamp TS(Ti) and a new transaction Tj enters the system, then TS(Ti )