Product Documentation

FairCom ISAM for C

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Conditional Expressions and Partition Rules

Conditional expressions make it easy to build a partition rule. A partition rule is a conditional expression ultimately evaluating to a number. That number associates data with a specific partition within the file.

FairCom DB expression parsing can now evaluate an expression into a numeric representation to be used for the partition rule. Many built-in conditional expression functions exist for flexible rule generation. Time and date based functions, numeric functions, and string manipulation functions are all available. FairCom DB expression syntax can even reference complex functions via an external shared library (DLL) in calculating partition numbers.

If the table has an embedded DODA resource and a conditional expression references schema segments, an expression can refer to index key fields explicitly by DODA name. Together with field names, complex expression rules can be crafted.

Prior to FairCom DB V11, partitioned files required these rules to be hard-coded at compile time (specified in ctpart.c) and did not allow run-time flexibility in adapting rules for unique deployed environments.

By combining existing FairCom DB advanced support for conditional expressions with our high performing partitioned files, applications can now create exact expression rules directly when creating partitioned files. In addition, existing partitioned files can have their partition rule changed and subsequently rebuilt based on a new rule logic allowing applications to grow and adapt with their customer needs.

Partitioned files are supported directly from the FairCom DB ISAM API, c-treeDB and FairCom DB SQL.


Additional processing of advanced expression parsing can potentially impact performance to a small degree. Should performance become an issue, you might consider an external DLL to efficiently evaluate partition rules directly.