When a domain is set up, its servers receive their first versions of the domain's NIS+ tables. These versions are stored on disk, but when a server begins operating, it loads them into memory. When a server receives an update to a table, it immediately updates its memory-based version of the table. When it receives a request for information, it uses the memory-based copy for its reply.
Of course, the server also needs to store its updates on disk. Since updating disk-based tables takes time, all NIS+ servers keep log files for their tables. The log files are designed to temporarily store changes made to the table, until they can be updated on disk. They use the table name as the prefix and append .log. For example:
hosts.org_dir.log bootparams.org_dir.log password.org_dir.log ipnodes.org_dir.log
You should update disk-based copies of a table on a daily basis so that the log files don't grow too large and take up too much disk space. This process is called checkpointing. To do this, use the nisping -C command.