static int getSchemaVersion(ZNRecord znRecord) {
    String schemaVersionStr = znRecord.getSimpleField(SCHEMA_VERSION_STR);
    return schemaVersionStr == null ? 0 : Integer.parseInt(schemaVersionStr);
  }
Get the schema version associated with the given instance (if any).
@param znRecord the {@link ZNRecord} associated with the interested instance.
@return the schema version of the information stored. If the field is absent in the InstanceConfig, the version
        is assumed to be 0, and 0 is returned.
ambry-clustermap/src/main/java/com/github/ambry/clustermap/ClusterMapUtils.java