套件： libjavaewah-java (0.7.9-1~18.04.1)

Compressed variant of the Java bitset class

The bit array data structure is implemented in Java as the BitSet class. Unfortunately, this fails to scale without compression.

JavaEWAH is a word-aligned compressed variant of the Java bitset class. It uses a 64-bit run-length encoding (RLE) compression scheme. It trades-off some compression for better processing speed. It also has a 32-bit version which compresses better, but is not as fast.

In general, the goal of word-aligned compression is not to achieve the best compression, but rather to improve query processing time. Hence, the class tries to save CPU cycles, maybe at the expense of storage. However, the EWAH scheme implemented is always more efficient storage-wise than an uncompressed bitmap as implemented in the BitSet class). Unlike some alternatives, javaewah does not rely on a patented scheme.