Kbase P49032: What are the advantages of a multi-volume versus a single-volume database?
| Autor |
Progress Software Corporation - Progress |
| Acesso |
Público |
| Publicação |
06/04/2004 |
|
Status: Unverified
GOAL:
What are the advantages of a multi-volume versus a single-volume database?
GOAL:
What are the differences between a single-volume and multi-volume database?
FACT(s) (Environment):
Progress 7.x
FACT(s) (Environment):
Progress 8.x
FIX:
The following is adapted from the v8 documentation. From v9 onwards all Progress databases are multi-volume.
Multi-volume vs. Single-volume Databases
PROGRESS applications operate identically, whether you use a multi-volume or single-volume database. To decide whether to use a multi-volume or single-volume database, you must understand the structural differences between these types of databases -
1. Single-volume Databases
A single-volume database is a database that is limited to one file system or physical volume. When you create a database with the PRODB utility, the Data Dictionary, or the Data Administration tool, PROGRESS creates a single-volume database.
Each PROGRESS database is contained in two files: your database (DB) file and your before-image (BI) file. The DB file defines the structure of your database and contains all of the data for your application tables and indexes. As you work with a single-volume database, PROGRESS logs all changes to your before-image file. This file contains data sufficient to undo active transactions and recover your database to a consistent state in the event of a system failure.
2. Multi-volume Databases
A multi-volume database extends across up to 256 disk volumes or file systems. Because of the distinct structural differences between single-volume and multi-volume databases, there are more steps involved in creating a multi-volume database than there are in creating a single-volume database. However, multi-volume databases can significantly improve performance and eliminate disk space and I/O contention issues, since files can be spread across different disks.
3. Choosing a Single-volume or Multi-volume Database
Consider the following guidelines when deciding whether to use a single-volume or multi-volume database:
- PROGRESS limits the size of individual files to a maximum of 2GB; however, some operating systems have lower limits. The maximum database size for UNIX and Windows is 2GB. You can overcome the single-volume database restrictions caused by operating system file size limitations. Because single-volume databases are, by definition, restricted to one file system, a database might eventually reach the limit of the file system on which it resides.
- Using multi-volume databases generally improves system performance. Extents for a multi-volume database can be stored across several disks, for example, reducing I/O resource contention.
- With a multi-volume database, you can back up your after-image (AI) files without shutting down your database.
- Because a multi-volume database contains more files than a single-volume, more file descriptors may be required on UNIX systems.
Note that prior to v9 the total bi file size (the total sum of all bi extents) cannot exceed 2GB, even for a multi-volume database.