Release 10.1A: OpenEdge Getting Started:
Database Essentials

Other block types

There are several other types of blocks that are valuable to understand. These include:

Master blocks
Storage object blocks
Free blocks
Empty blocks

Master blocks

The master block contains the same 16-byte header as other blocks, but this block is used to store status information about the entire database. It is always the first block in the database and is found in Area 6. This block contains the database version number, total allocated blocks, time stamps, and status flags. You can retrieve additional information from this block using the Virtual System Table (VST) _mstrblk. For more information on VSTs, see OpenEdge Data Management: Database Administration .

Storage object blocks

Storage object blocks contain the addresses of the first and last records in every table by each index. If a user runs a program that requests the first or find last record in a table, it is not necessary to traverse the index. The database engine obtains the information from the storage object block and goes directly to the record. Storage object blocks are frequently used, so these blocks are pinned in memory. This availability further increases the efficiency of the request.

Free blocks

Free blocks have a header, but no data is stored in the blocks. These blocks can become any other valid block type. These blocks are below the high-water mark. The high-water mark is a pointer to the last formatted block within the database storage area. Free blocks can be created by extending the high-water mark of the database, extending the database, or reformatting blocks during an index rebuild. If the user deletes many records, the RM blocks are put on the RM Chain. However, index blocks can be reclaimed only through an index rebuild or an index compress.

Empty blocks

Empty blocks do not contain header information. These blocks must be formatted prior to use. These blocks are above the high-water mark but below the total number of blocks in the area. The total blocks are the total number of allocated blocks for the storage area.