Notes on Working with Data (D) Nodes
For performance reasons, the SSR ndbmtd processes on data (D) nodes are configured to execute under the UNIX root account by default, as opposed to the UNIX hadm account. In particular, this allows the ndbmtd processes to lock data in physical memory, which is faster, as opposed to allowing the OS to use swap space on disk, which is slower. The UNIX root account privilege is required in order to lock data in physical memory.
The relevant configuration item is the #sbrd-ndbd-run-as-root = true parameter in the [ndbd] section of the /opt/JNPRhadm/my.cnf file. Note that the leading # character is required to distinguish this parameter as a sbrd script parameter; this parameter is not a comment and is always active. When the value of this parameter is true, the ndbmtd processes execute under the UNIX root account. When the value of this parameter is false (or if the parameter is missing entirely), the ndbmtd processes execute under the UNIX hadm account. The value of this parameter can only be changed immediately after configuring a data (D) node. The value of this parameter cannot be changed after the SSR processes are running.
We recommend, although it is not necessary, that the parameter be configured the same on all data (D) nodes. In order to change the value of this parameter at a later time, you must unconfigure the data (D) node and then reconfigure it again.
When the ndbmtd processes are executed under the UNIX root account, it is extremely important that the DataMemory parameter in the [ndbd default] section of the /opt/JNPRhadm/config.ini file be configured properly with respect to the amount of physical memory that is actually available on the data (D) node. If the data (D) node does not have enough physical memory available, then the ndbmtd processes can starve the entire machine, including the OS itself, for memory. By default, SBRC is configured under the assumption that at least 8 GB of memory is available solely for ndbmtd processes. In practice, more than 8 GB is required to support the OS and other applications.