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Database Essentials
Administrative Planning : Data layout : Sizing your database areas : Specifying records per block
Specifying records per block
OpenEdge allows you specify a maximum number of records per block per area value within the range of 1 to 256. The number of records per block must be a power of 2 (1, 2, 4, 8..., 256). Depending on the actual size of your record, you might not be able fit the specified maximum number of records in a block.
To determine the number of records per block:
1. Take the mean record size from your table analysis.
2. Add 2 to the record size for the directory entry overhead. The mean record size includes the record overhead, but excludes the directory entry overhead.
3. For an 8K block size, divide 8192 by the number in Step 2. For a 4K block size, divide 4096 by the number in Step 2.
4. Round the number from Step 3 up or down to the closest power of 2.
Most of the time, the record length will not divide into this number evenly so you must make a best estimate. If your estimate includes too many records per block, you run the risk of fragmentation (records spanning multiple blocks). If your estimate includes too few records per block, you waste space in the blocks. The goal is to be as accurate as possible without making your database structure too complex.