public String displayName() {
    return displayName;
  }
Operation types representing snapshots of the table.
<li>ALL: all operations, contain optimizing and non-optimizing.
<li>OPTIMIZING: Indicates that this snapshot is generated by optimization.
<li>NON_OPTIMIZING: Indicates that this snapshot is generated by non-optimization.
amoro-common/src/main/java/org/apache/amoro/table/descriptor/OperationType.java