Run-length compression of index keys

摘要

The invention is a compression method which provides the advantages of run-length compression while preserving the natural collating order of the data. The method of the invention replaces sequential repetitions of a target pattern beyond a threshold value followed by a single number which encodes both the repetition count and the collating relationship between the target pattern and the pattern which follows it in the uncollated sequence. In the preferred embodiment of the invention, the code is preceded by at least one repetition of the pattern. In the preferred embodiment of the invention, the numerical code is set as the difference between the run count and the threshold count if the following pattern is less than the target pattern, or if there is no following pattern. If the following pattern is greater than the compression sequence, the code is set as a predetermined number, preferably the maximum binary value of the sequence length, minus the difference between the run count and the threshold count.