Some other projects that arent pure database file systems but that use some

Some other projects that arent pure database file

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Some other projects that aren't "pure" database file systems but that use some aspects of a database file system: A lot of Web-CMS use a relational DBMS to store and retrieve files. Examples: XHTML files are stored as XML or text fields, image files are stored as blob fields; SQL SELECT (with optional XPath) statements retrieve the files, and allow the use of a sophisticated logic and more rich information associations than "usual file systems". Very large file systems, embodied by applications like Apache Hadoop and Google File System, use some database file system concepts. Transactional file systems Some programs need to update multiple files "all at once". For example, a software installation may write program binaries, libraries, and configuration files. If the software installation fails, the program may be unusable. If the installation is upgrading a key system utility, such as the command shell, the entire system may be left in an unusable state. Transaction processing introduces the isolation guarantee, which states that operations within a transaction are hidden from other threads on the system until the transaction commits, and that interfering operations on the system will be properly serialized with the transaction. Transactions also provide the atomicity guarantee, that operations inside of a transaction are either all committed, or the transaction can be aborted and the system discards all of its partial results. This means that if there is a crash or power failure, after recovery, the stored state will be consistent. Either the software will be completely installed or the failed installation will be completely rolled back, but an unusable partial install will not be left on the system. Windows, beginning with Vista, added transaction support to NTFS, abbreviated TxF. There are a number of research prototypes of transactional file systems for UNIX systems, including the Valor file system, [2] Amino, [3] LFS, [4] and a transactional ext3 file system on the TxOS kernel, [5] as well as transactional file systems targeting embedded systems, such as TFFS. [6] Ensuring consistency across multiple file system operations is difficult, if not impossible, without file system transactions. File locking can be used as a concurrency control
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mechanism for individual files, but it typically does not protect the directory structure or file metadata. For instance, file locking cannot prevent TOCTTOU race conditions on symbolic links. File locking also cannot automatically roll back a failed operation, such as a software upgrade; this requires atomicity. Journaling file systems are one technique used to introduce transaction-level consistency to file system structures. Journal transactions are not exposed to programs as part of the OS API; they are only used internally to ensure consistency at the granularity of a single system call.
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