public static long nextSegmentId() {
        long mine = nextSegmentId.incrementAndGet();
        if (mine > MAX_SEGMENT_ID) {
            throw new Error("Run out of segment id, knock the guy who wrote this code and reboot process.");
        }
        return mine;
    }
The id for IntegratedSegment, unique in local JVM.
Only used for cache.
indexr-segment/src/main/java/io/indexr/segment/cache/MemCache.java