These older databases often allow the use of indexes as an option. Of course ISAM (Indexed Sequential Access Method) is indexed. But also it is often possible t

These older databases often allow the use of indexes as an option. Of course ISAM (Indexed Sequential Access Method) is indexed. But also it is often possible to add indexes to the networked database internal structures. An alternative is to use hash tables with overflow. In any case you must usually periodically scan through the database reorganizing the indices and/or location of records, which can take up a lot of time and usually requires taking the database offline. Here's a good read(first is PDF): https://www.google.com/url?q=http://advsys.net/ghs/publications/DBReorgPAP.pdf&sa=U&ved=0ahUKEwiznqms3vTNAhVC7GMKHdpyC7cQFggUMAA&usg=AFQjCNGMpZbH9wAWbDq-6FiMhtn1fBIg4w https://www.google.com/url?q=http://advsys.net/ghs/publicati... or the same paper at Google Books: https://books.google.com/books?id=YqM3pqFVt8IC&pg=PA8&lpg=PA4&ots=ehTAPwbseo&focus=viewport&dq=CODASYL++REORG https://books.google.com/books?id=YqM3pqFVt8IC&pg=PA8&lpg=PA...