NDB Cluster Configuration Files The  type  attribute represents an NDB thread type. The thread types supported, and the range of permitted  count  values for each, are provided in the following list: Each LDM thread is normally grouped with 1 query thread to form an LDM group. A set of 4 to 8 LDM groups is grouped into a round robin groups. Each LDM thread can be assisted in execution by any query or threads in the same round robin group.  NDB  attempts to form round robin groups such that all threads in each round robin group are locked to CPUs that are attached to the same L3 cache, within the limts of the range stated for a round orbin group’s size. Changing the number of LDM threads normally requires a system restart to be effective and safe for cluster operations; this requirement is relaxed in certain cases, as explained later in this section. This is also true when this is done using  MaxNoOfExecutionThreads . Adding large tablespaces (hundreds of gigabytes or more) for Disk Data tables when using more than the default number of LDMs may cause issues with resource and CPU usage if DiskPageBufferMemory  is not sufficiently large. A query thread also acts as a recovery thread (see next item), although the reverse is not true. Changing the number of query threads requires a node restart. Changing the number of recovery threads requires a node restart. Optimally, every new transaction can be assigned to a new TC thread. In most cases 1 TC thread per 2 LDM threads is sufficient to guarantee that this can happen. In cases where the number of writes is relatively small when compared to the number of reads, it is possible that only 1 TC thread per 4 LQH threads is required to maintain transaction states. Conversely, in applications that perform a 4136 • tc : Transaction coordinator thread ( DBTC  kernel block) containing the state of an ongoing transaction. In NDB 8.0.23 and later, the maximum number of TC threads is 128; previously, this was 32. • recover  (Added in NDB 8.0.23): A recovery thread restores data from a fragment as part of an LCP. • query  (Added in NDB 8.0.23): A query thread is tied to an LDM and together with it forms an LDM group; acts only on  READ COMMITTED  queries. The number of query threads must be set to 0, 1, 2, or 3 times the number of LDM threads. Query threads are not used, unless this is overridden by setting query  to a nonzero value, or by enabling the  AutomaticThreadConfig  parameter, in which case LDMs behave as they did prior to NDB 8.0.23. • ldm : Local query handler ( DBLQH  kernel block) that handles data. The more LDM threads that are used, the more highly partitioned the data becomes. (Beginning with NDB 8.0.23, when ClassicFragmentation  is set to 0, the number of partitions is independent of the number of LDM threads, and depends on the value of  PartitionsPerNode  instead.) Each LDM thread maintains its own sets of data and index partitions, as well as its own redo log. Prior to NDB 8.0.23, the value set for ldm  must be one of the values 1, 2, 4, 6, 8, 12, 16, 24, or 32. In NDB 8.0.23 and later, it is possible to set  ldm  to any value in the range 1 to 332 inclusive; it also becomes possible to set it to 0, provided that  main ,  rep , and  tc  are also 0, and that  recv  is set to 1; doing this causes  ndbmtd  to emulate ndbd . thread_prio  value Windows thread priority 8 - 10 THREAD_PRIORITY_HIGHEST