Btrieve Interactive Maintenance Utility

Btrieve Interactive Maintenance Utility

The Interactive Maintenance utility is a Windows application that runs on Windows 32-bit and 64-bit platforms. Use this utility if you prefer a graphical interface or if you want to create a description file. This section contains the following major topics:

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File Information Editor

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Managing Owner Names

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Statistics Report

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Each major topic contains tasks specific to that topic.

Extended File Support

The size of a MicroKernel data file can be larger than the operating system file size limit. When you export data from an extended MicroKernel file to an unformatted file, the size of the unformatted file can exceed the database engine file size limit because of the differences in the physical format.

When you are exporting large files, the Interactive Maintenance utility detects when the unformatted file exceeds a 2 GB file size limit and starts creating extension files. This process is transparent. Extension files and the original unformatted file must reside on the same volume. (The size limit for a file varies depending on the operating system and file system. The 2 GB size is simply the limit enforced by the database engine.)

The extension file uses a naming scheme in which the file names are similar to the base file name. In contrast to native MicroKernel Engine extension files which use a caret “^” to indicate extension file status, the unformatted extension files use a tilde “~” to avoid overwriting any existing extended engine files with the same base file name. The first export extension file is the same base file name with “.~01” extension. The second extension file is “.~02,” and so on. These extensions are appended in hexadecimal format.

The naming convention supports up to 255 extension files, thus supporting files as large as 256 GB.

Additionally, when you import data from an unformatted file, the utility detects whether the file has extensions and loads the data from the extension file.

Long File Names and Embedded Spaces Support

Long file name support, including support for embedded spaces is available in all supported operating system environments. All references to files can contain embedded spaces and be longer than 8 bytes.

Older versions of Btrieve allowed spaces to be added at the end of a file name in path-based operations such as Open and Create. This is still the default behavior. Existing applications will not break. However, if you want to take advantage of file and directory names with embedded spaces, set the Embedded Spaces configuration setting for the client requester to On. Note that On is the default setting.

Even when you turn the option off an application that accesses a file having a name with embedded spaces can enclose that name in double quotes while making the BTRV/BTRVID/BTRCALL/BTRCALLID call to open or create the file.

Record and Page Compression

PSQL provides two types of data compression: record and page. These two types may be used separately or together. The primary purpose for both compression types is to reduce the size of the data files and to provide faster performance depending on the type of data and on the type of data manipulation.

Record Compression

Record compression requires a file format of 6.0 or later. Record compression can result in a significant reduction of the space needed to store records that contain many repeating characters. The database engine compresses five or more of the same contiguous characters into 3 bytes.

When creating a file, the database engine automatically uses a page size larger than what is specified to allow room for the specified record length. If the uncompressed record length is too large to fit on the largest available page, the database engine automatically turns on record compression.

Because the final length of a compressed record cannot be determined until the record is written to the file, the database engine creates a file with record compression as a variable-length record file. Compressed images of the records are stored as variable-length records. Individual records may become fragmented across several file pages if your application performs frequent insertions, updates, and deletions. The fragmentation can result in slower access times because the database engine may need to read multiple file pages to retrieve a single record.

See also Choosing a Page Size, Estimating File Size, and Record Compression, all in PSQL Programmer's Guide in the Developer Reference.

Page Compression

Page compression requires a file format of 9.5 or later. Internally, a PSQL data file is a series of different types of pages. Page compression controls the compression and decompression of data pages within a file.

As a file is read from physical storage, data pages are decompressed and held in a memory cache. Record reads and updates are performed against the uncompressed data in the memory cache. When a write action occurs, the data page is compressed then written to physical storage. Depending on cache management, the compressed page is also retained in memory until accessed again.

If the type of data cannot be significantly compressed, the database engine writes the data to physical storage uncompressed.

Deciding When To Use Compression

The benefits obtained by using record compression, page compression, or both depends entirely on the type of data being compressed. Given that, the following table discusses some general factors to consider when deciding to use data compression or not.

Table 69

Factors To Consider Pertaining to Data Compression

Factors to Consider

Record compression is most effective for the following conditions:

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Each record has the potential for containing a large number of repeating characters. For example, a record may contain several fields, all of which may be initialized to blanks by your task when it inserts the record into the file. Record compression is more efficient if these fields are grouped together in the record, rather than being separated by fields containing other values.

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The computer running the database engine can supply the extra memory required for compression buffers.

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The records are read much more frequently than they are changed.

If the fixed length portion of a record is longer than the page size minus overhead, compression is used automatically.

Note that you cannot use record compression for key-only files or for files that use blank truncation.

Page compression is most effective for the following conditions:

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Data is highly compressible using a ZIP-type compression algorithm. When the file size can be significantly decreased because of page compression, such as 4 to 1 compression, file performance can be increased significantly.

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The pages are read much more frequently than they are inserted, updated, or deleted.

Note that the database engine writes data pages to physical storage uncompressed if the data cannot be significantly compressed.

The use of record compression and page compression is most effective when records contain a large proportion of blank space and the pages are read much more frequently than they are inserted, updated, or deleted.

The Btrieve Maintenance Utility Interface

Access Maintenance from the operating system Start menu or Apps screen or from the Tools menu in PSQL Control Center. The Maintenance main window looks like the following.

Figure 18 Btrieve Maintenance Utility Main Window

The interactive Maintenance utility provides the following menus:


Options	Allows you to display the File Information Editor, set and clear owner names, generate statistics reports, and exit the utility.
Index	Allows you to create and drop indexes.
Data	Allows you to load data from ASCII files, save data to ASCII files, copy records between data files, and perform a roll forward operation to recover changes made to a data file between the time of the last backup and a system failure.
Help	Provides access to the Maintenance utility help system.

To access the Maintenance utility help system, click Help in the dialog box for which you want help, or choose a command from the Help menu, as follows:


Contents	Provides a list of Maintenance utility help topics.
About	Displays copyright information and the product version number.