Category Archives: General

ACID

In computer science, ACID (Atomicity, Consistency, Isolation, Durability) is a set of properties that guarantee that database transactions are processed reliably. In the context of databases, a single logical operation on the data is called a transaction. For example, a transfer of funds from one bank account to another, even involving multiple changes such as debiting one account and crediting another, is a single transaction.

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Daemon

In Unix and other multitasking computer operating systems, a daemon is a computer program that runs as a background process, rather than being under the direct control of an interactive user. Typically daemon names end with the letter d: for example, syslogd is the daemon that implements the system logging facility and sshd is a daemon that services incoming SSH connections.

In a Unix environment, the parent process of a daemon is often, but not always, the init process. A daemon is usually created by a process forking a child process and then immediately exiting, thus causing init to adopt the child process. In addition, a daemon or the operating system typically must perform other operations, such as dissociating the process from any controlling terminal (tty). Such procedures are often implemented in various convenience routines such as daemon in Unix.

Systems often start daemons at boot time: they often serve the function of responding to network requests, hardware activity, or other programs by performing some task.

Copy-Modify-Merge Solution

Subversion, CVS, and many other version control systems use a copy-modify-merge model as an alternative to locking. In this model, each user’s client contacts the project repository and creates a personal working copy—a local reflection of the repository’s files and directories. Users then work simultaneously and independently, modifying their private copies. Finally, the private copies are merged together into a new, final version. The version control system often assists with the merging, but ultimately, a human being is responsible for making it happen correctly.

Lock-Modify-Unlock Solution

Many version control systems use a lock-modify-unlock model to address the problem of many authors clobbering each other’s work. In this model, the repository allows only one person to change a file at a time. This exclusivity policy is managed using locks. one must lock the before making any changes to the files so that any other can not access the file .