NDB Cluster Configuration Files 3. Setting  ndb_data_node_neighbour  further decreases the effective  Group  value by 50, causing this node to be regarded as the nearest node. This is needed only when all data nodes are on hosts other than that hosts the API node and it is desirable to dedicate one of them to the API node. In normal cases, the default adjustment described previously is sufficient. • ndb_read_backup • ndb_recv_thread_cpu_mask Frequent changes in  ndb_data_node_neighbour  are not advisable, since this changes the state of the cluster connection and thus may disrupt the selection algorithm for new transactions from each thread until it stablilizes. Command-Line Format --ndb-recv-thread-cpu-mask=mask 4187 Command-Line Format --ndb-recv-thread-activation- threshold=# System Variable ndb_recv_thread_activation_threshold Scope Global Dynamic Yes SET_VAR  Hint Applies No Type Integer Default Value 8 Minimum Value 0 (MIN_ACTIVATION_THRESHOLD) Maximum Value 16 (MAX_ACTIVATION_THRESHOLD) Command-Line Format --ndb-read-backup[={OFF|ON}] System Variable ndb_read_backup Scope Global Dynamic Yes SET_VAR  Hint Applies No Type Boolean Default Value ( ≥  8.0.19-ndb-8.0.19) ON Default Value ( ≤  8.0.18-ndb-8.0.18) OFF • ndb_recv_thread_activation_threshold This variable is global in scope. It can also be set at startup. When this number of concurrently active threads is reached, the receive thread takes over polling of the cluster connection. To enable or disable read from any fragment replica for an individual table, you can set the  NDB_TABLE option  READ_BACKUP  for the table accordingly, in a  CREATE TABLE  or  ALTER TABLE  statement; see Section 13.1.20.11, “Setting NDB_TABLE Options” , for more information. Enable read from any fragment replica for any  NDB  table subsequently created; doing so greatly improves the table read performance at a relatively small cost to writes.