ENSCRIBE

Enscribe is one of the database for HP Non Stop Tandem, it is a file system database which has.

  • High Level Access to Database.

  • Ensures Data Integrity.

  • Partitioned Files.

  • Five disk file structures.

  • Transaction auditing through TMF.

Some of the features & terminology used for Ensribe file systems:

  • File – Collection of records.

  • Format 1 and Format 2 – It’s a static attribute and is established when the file is created. If the size of the file is less then 2GB-1MB then its format 1 file else Format 2 file.

  • Cache buffering.

  • Record locking and file locking.

  • Sector – The smallest unit of disk I/O.

  • Extents – A Unit of storage allocation for a file to be allotted as contiguous space on disk. 1 extent = 2048 byte pages.

  • Block – The unit of physical I/O.

  • Partitioned files – Partitioned files are different copies of same file on different volumes, once can partition a file across network nodes, up to 16 partitions are permitted.

TYPES OF FILE STRUCTURES

UNSTRUCTURED

Thiis type of file is viewed as a string of bytes by the file management system. The file system presents a block of data to the user, and it is up to the user process to deblock the logical records. Mostly these files are used as an edit file. The file system knows the EOF and extent sizes.

STRUCTURED

This type of file is further classified into 4 types.Data transfer between application process and disk files are done in terms of logical records and record keys.

  • Entry-Sequenced – Variable record size and record is inserted at the EOF of file. The primary key is a block number and a record number which is external to data record.

  • Key-Sequenced – Variable record size; record can be inserted in primary key sequence. The primary key is a particular data field, designated by user within each data record.

  • Relative – Variable record size; record can be inserted in any free slot in file. The primary key is an ordinal number which is external to data record.

  • Queue – variable record size with minimum 8 bytes to hold timestamp, record inserted in free space in block or at the End of the file. The primary key resides within the data record and consists of an 8 byte timestamp plus an optional user key.

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