Edit conflict
An edit conflict is a computer problem that may occur when multiple editors edit the same file during a short time period.

Description 
The conflict occurs when an editor gets a copy of a shared document file, changes the copy, and attempts to save the changes to the original file, which has been altered by another editor after the copy was obtained.

Resolution 
The simplest way to resolve an edit conflict is to ignore intervening edits and overwrite the current file. This may lead to a substantial loss of information, and alternative methods are often employed to resolve or prevent conflicts.
 Manual resolution, where the editor determines which version to retain and may manually incorporate edits into the current version of the file.
 Store a backup, or data backup is a copy of computer data taken and stored elsewhere so that it may be used to restore the original after a data loss event or file comparisons of each edit, so there are backups changes of the file once the original is overwritten. Backups can be used to recover data after its loss from data deletion or corruption, or to recover data from an earlier time. Backups provide a simple form of disaster recovery; however not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server. A backup system contains at least one copy of all data considered worth saving. The data storage requirements can be large. An information repository model may be used to provide structure to this storage. There are different types of data storage devices used for copying backups of data that is already in secondary storage onto archive .  There are also different ways these devices can be arranged to provide geographic dispersion, data security, and Portability. Data is selected, extracted, and manipulated for storage. The process can include methods for dealing with live data, including open files, as well as compression, encryption, and de-duplication. Additional techniques apply to enterprise client-server backup. Backup schemes may include dry runs that validate the reliability of the data being backed up. There are limitations[5] and human factors involved in any backup scheme. 
 File locking, which limits the file to one editor at a time to prevent edit conflicts. File locking is a mechanism that restricts access to a computer file, or to a region of a file, by allowing only one user or process to modify or delete it at a specific time and to prevent reading of the file while it's being modified or deleted.

Systems implement locking to prevent the classic interceding update scenario, which is a typical example of a race condition, by enforcing the serialization of update processes to any given file. The following example illustrates the interceding update problem:

    Process A reads a customer record from a file containing account information, including the customer's account balance and phone number.
    Process B now reads the same record from the same file, so it has its own copy.
    Process A changes the account balance in its copy of the customer record and writes the record back to the file.
    Process B, which still has the original stale value for the account balance in its copy of the customer record, updates the account balance and writes the customer record back to the file.
    Process B has now written its stale account-balance value to the file, causing the changes made by process A to be lost.

Most operating systems support the concept of record locking, which means that individual records within any given file may be locked, thereby increasing the number of concurrent update processes. Database maintenance uses file locking, whereby it can serialize access to the entire physical file underlying a database. Although this does prevent any other process from accessing the file, it can be more efficient than individually locking many regions in the file by removing the overhead of acquiring and releasing each lock.

Poor use of file locks, like any computer lock, can result in poor performance or in deadlocks. File locking may also refer to additional security applied by a computer user either by using Windows security, NTFS permissions or by installing a third party file locking software. Computer writer Gary B. Shelly notes that many wiki systems "will block the contributor who is attempting to edit the page from being able to do so until the contributor currently editing the page saves changes or remains idle on the page for an extended period of time."
 Merge, by determining if the edits are in unrelated parts of the file and combining without user intervention. In version control, merging (also called integration) is a fundamental operation that reconciles multiple changes made to a version-controlled collection of files. Most often, it is necessary when a file is modified on two independent branches and subsequently merged. The result is a single collection of files that contains both sets of changes.

In some cases, the merge can be performed automatically, because there is sufficient history information to reconstruct the changes, and the changes do not conflict. In other cases, a person must decide exactly what the resulting files should contain. Many revision control software tools include merge capabilities.
file comparisons.This article compares computer software tools which are used for accomplishing comparisons of files of various types. The file types addressed by individual file comparison apps varies, but may include text, symbols, images, audio, or video. This category of software tool is often called "file comparison" or "diff tool", but those effectively are equivalent terms — where the term "diff" is more commonly associated with the Unix diff utility.

A typical rudimentary case is the comparison of one file against another. However, it also may include comparisons between two populations of files, such as in the case of comparing directories or folders, as part of file management. For instance, this might be to detect problems with corrupted backup versions of a collection of files ... or to validate a package of files is in compliance with standards before publishing.

Note that comparisons must be made among the same file type. Meaning, a text file cannot be compared to a picture containing text, unless an optical character reader (OCR) process is done first to extract the text. Likewise, text cannot be compared to spoken words, unless the spoken words first are transcribed into text. Additionally, text in one language cannot be compared to text in another, unless one is translated into the language of other.

A critical consideration is how the two files being compared must be substantially similar and thus not radically different. Even different revisions of the same document — if there are many changes due to additions, removals, or moving of content — may make comparisons of file changes very difficult to interpret. This suggests frequent version saves of a critical document, to better facilitate a file comparison.

A "diff" file comparison tool is a vital time and labor saving utility, because it aids in accomplishing tedious comparisons. Thus, it is a vital part of demanding comparison processes employed by individuals, academics, legal arena, forensics field, and other professional endeavors — to identify sometimes hard to spot differences needed for detecting.

Occurrences 
The problem is encountered on heavily edited articles in wikis (frequency higher in articles related to a current event or person), distributed data systems (e.g., Google Sites), and  revision control systems not using file locking.  as well as other high-traffic pages. If a significant amount of new text is involved, the editor who receives an "edit conflict" error message can cut and paste the new text into a word processor or similar program for further editing, or can paste that text directly into a newer version of the target document.  Simple copyediting can be done directly on the newer version, and then saved.

See also
 Concurrent Versions System
 Apache Subversion
 Git (software)

References

Wiki concepts
Version control
Distributed computing problems