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The Lamport timestamp algorithm is a simple logical clock algorithm used to determine the order of events in a distributed computer system.As different nodes or processes will typically not be perfectly synchronized, this algorithm is used to provide a partial ordering of events with minimal overhead, and conceptually provide a starting point for the more advanced vector clock method.
Software timekeeping systems vary widely in the resolution of time measurement; some systems may use time units as large as a day, while others may use nanoseconds.For example, for an epoch date of midnight UTC (00:00) on 1 January 1900, and a time unit of a second, the time of the midnight (24:00) between 1 January 1900 and 2 January 1900 is represented by the number 86400, the number of ...
The term "timestamp" derives from rubber stamps used in offices to stamp the current date, and sometimes time, in ink on paper documents, to record when the document was received. Common examples of this type of timestamp are a postmark on a letter or the "in" and "out" times on a time card.
In computer science and computer programming, system time represents a computer system's notion of the passage of time. In this sense, time also includes the passing of days on the calendar . System time is measured by a system clock , which is typically implemented as a simple count of the number of ticks that have transpired since some ...
update: Update the files in a working copy with the latest version from a repository; lock: Lock files in a repository from being changed by other users; add: Mark specified files to be added to repository at next commit; remove: Mark specified files to be removed at next commit (note: keeps cohesive revision history of before and at the remove.)
Some of the metadata is maintained by the file system, for example last-modification date (and various other dates depending on the file system), location of the beginning of the file, the size of the file and if the file system backup utility has saved the current version of the files. These items cannot usually be altered by a user program.
For example, if a programmer declares a function as returning a timestamp type, this documents the function when the timestamp type can be explicitly declared deeper in the code to be an integer type. Advantages provided by compiler-specified type systems include: Optimization – Static type-checking may provide useful compile-time information ...
A vector clock of a system of N processes is an array/vector of N logical clocks, one clock per process; a local "largest possible values" copy of the global clock-array is kept in each process. Denote V C i {\displaystyle VC_{i}} as the vector clock maintained by process i {\displaystyle i} , the clock updates proceed as follows: [ 1 ]