Product Documentation

FairCom ISAM for C

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Leading Character Compression Keys

Key type 4 is for fixed length keys that are likely to have significant leading character duplication among the key values. The common beginnings of successive key values are represented by a compression byte count. Consider the following sequence of key values:




With leading character compression enabled, these 24-bytes could be represented by the following 18-bytes:




The integers preceding the key values indicate the number of leading characters that the key value shares in common with the immediately preceding key value.

Note: Key compression imposes a significant performance impact, especially when deleting records. Use this feature only when absolutely necessary to keep index space requirements to a minimum.