Setting TTL for Data

You can delete stale JSON documents in JSON tables automatically by setting a time-to-live (TTL) value on the column family.

TTL is set only on the default column family in a JSON table. The duration that you set applies to each entire JSON document in the JSON table.

NOTE
Only the default column family can exist in order to set TTL; no other column families can exist in the JSON table. You also cannot set the TTL for a JSON table if it has secondary indexes.

Data can become stale. If the data in an JSON document has not been updated within a certain period of time, you might want to delete the document. In the case of a large amount of JSON documents, applications should not have to track the time between updates and then delete the expired documents.

Because the time-to-live that is set on a column family affects an entire JSON table, only the default column family is allowed to have a non-default time-to-live value. In addition, to prevent multiple column families from having non-default time-to-live values, additional column families can not be created in a table if the default column family has a non-default value. This is because if more than one column family had a non-default TTL value, fragments of documents would expire at different times, leading to inconsistent views of data.

Permission Required

The writeAce permission on the volumes where the JSON tables are located. For information about how to set permissions on volumes, see Setting Whole Volume ACEs.

Example: Setting the default column family to a non-default time-to-live value

If you set the time-to-live parameter for the default column family to 864,000 seconds, JSON documents in that table are considered to be stale if the document's data has not been updated within 10 days and are automatically deleted.

The following code example creates a JSON table, the default column family and sets the TTL to a non-default value of 10 days (864,000 seconds). 

/* Create a TableDescriptor for the table to create,
   passing in the path of the table. */
TableDescriptor tableDescriptor = MapRDB.newTableDescriptor(tablePath);

/* Create a FamilyDescriptor for the default column family.
   When you create a table with the API, you must also create
   the default column family.
   Set the TTL to 10 days.
   After creating the FamilyDescriptor, add it to 
   the TableDescriptor. */
FamilyDescriptor defaultfamilyDesc = MapRDB.newDefaultFamilyDescriptor()
   .setTTL(864000);
tableDescriptor.addFamily(defaultfamilyDesc);


// Pass the TableDescriptor to the Admin.createTable() method.
public void createJSONTable(String tablePath, TableDescriptor tableDescriptor) throws DBException {
  try (Admin admin = MapRDB.newAdmin()) {
    if (!admin.tableExists(tablePath)) {
      admin.createTable(tableDescriptor);
    }
  }
}