public int distributionBits() {
        int distributionBits;
        if (zoneEnvImplies16DistributionBits() && ! zone.equals(Zone.defaultZone())) {
            distributionBits = 16;
        }
        else { // hosted test zone, or self-hosted system
            // hosted test zones: have few nodes and use visiting in tests: This is slow with 16 bits (too many buckets)
            // self-hosted systems: should probably default to 16 bits, but the transition may cause problems
            distributionBits = getDistributionBits(getNodeCountPerGroup(), getDistributionMode());
        }

        // Avoid number of distribution bits being reduced
        if (distributionBitsInPreviousModel.isPresent() && distributionBitsInPreviousModel.get() > distributionBits)
            return distributionBitsInPreviousModel.get();

        return distributionBits;
    }
Returns the distribution bits this cluster should use.
On Hosted Vespa this is hardcoded and not computed from the nodes because reducing the number of nodes is a common
operation, while reducing the number of distribution bits can lead to consistency problems.
This hardcoded value should work fine from 1-200 nodes. Those who have more will need to set this value
in config and not remove it again if they reduce the node count.
config-model/src/main/java/com/yahoo/vespa/model/content/cluster/ContentCluster.java