Linux Certif

Toute la documentation sur la certification Linux LPI

dirfile

NAME

dirfile --- a filesystem based database format for time-ordered binary data

DESCRIPTION

The dirfile database format is designed to provide a fast, simple format for storing and reading binary time-ordered data. Dirfiles can be read using the GetData library.

The dirfile database is centred around one or more time-ordered data streams (a time stream). Each time stream is written to disk in a separate file, in its native binary format. The name of these binary files correspond to the time stream's field name. Two time streams may have different constant sampling frequencies and mechanisms exist within the dirfile format to ensure these time streams remain properly sequenced in time.

To do this, the time streams in the dirfile are subdivided into frames. Each frame contains an integer number of samples of each time stream. When synchronous retrieval of data from more than one time stream is required, position in the dirfile can be specified in frames, which will ensure synchronicity.

The binary files are all located in a central directory, known as the dirfile directory. The dirfile as a whole may be referred to by its dirfile directory path.

Included in the dirfile along with the time streams is the dirfile format specification, which is an ASCII text file called format located in the dirfile directory. This file fully specifies the dirfile's metadata. For the syntax of this file, see dirfile-format(5).

Version 3 of the Dirfile Standards introduced the large dirfile extension. This extension added the ability to distribute the dirfile metadata among multiple files (called fragments) in addition to the format file, as well as the ability to house portions of the database in subdirfiles. These subdirfiles may be fully fledged dirfiles in their own right, but may also be contained within a larger, parent dirfile. See dirfile-format(5) for information on specifying these subdirfiles.

In addition to the raw fields on disk, the dirfile format specification may also specify derived fields which are calculated from one or more raw or derived time streams. Derived fields behave identically to raw fields when read via GetData. See dirfile-format(5) for a complete list of derived field types. Dirfiles may also contain both numerical and character string constant scalar fields, also further outlined in dirfile-format(5).

Dirfiles are designed to be written to and read simultaneously. The dirfile specification dictates that one particular raw field (specified either explicitly or implicitly by the format file) is to be used as the reference field: all other vector fields are assumed to have at least as many frames as the reference field has, and the size (in frames) of the reference field is used as the size of the dirfile as a whole.

Version 6 of the Dirfile Standards added the ability to encode the binary files on disk. Each fragment may have its own encoding scheme. Notably this can be used to compress these files. See dirfile-encoding(5) for information on encoding schemes.

AUTHORS

The dirfile specification was developed by C. B. Netterfield <netterfield@astro.utoronto.ca>.

The dirfile specification is now maintained by D. V. Wiebe <dvw@ketiltrout.net>.

SEE ALSO

dirfile-encoding(5) dirfile-format(5)