I don't know how many people remember this, but this kind of "weird atomic replaces of the read-only data file" was very common on unix-systems for a long time.
Take sendmail: people would have their email-aliases in a /etc/aliases file, with a simple ascii-format, lines formatted according to: "<key>: <values...>". The "newaliases" command then would convert the content of the ASCII file /etc/aliases into the binary (originally: Berkeley db) /etc/aliases.db.
As far as I know, CDB was developed initially for qmail, DJBs email-daemon, for exactly that purpose.
Another example for this is the "Yellow-Pages" (yp) / NIS directory services to distribute usernames/userids/groups/... in a UNIX cluster or network. ASCII files were converted into e.g. /var/yp/DOMAIN/passwd.byname, a .db-file where keys are the usernames from /etc/passwd and values were the full ASCII lines from /etc/passwd, same goes for passwd.byuid, group.byname, and so on. All for fast indicing, so that the network server didn't have to repeatedly parse /etc/passwd.
Take sendmail: people would have their email-aliases in a /etc/aliases file, with a simple ascii-format, lines formatted according to: "<key>: <values...>". The "newaliases" command then would convert the content of the ASCII file /etc/aliases into the binary (originally: Berkeley db) /etc/aliases.db.
As far as I know, CDB was developed initially for qmail, DJBs email-daemon, for exactly that purpose.
Another example for this is the "Yellow-Pages" (yp) / NIS directory services to distribute usernames/userids/groups/... in a UNIX cluster or network. ASCII files were converted into e.g. /var/yp/DOMAIN/passwd.byname, a .db-file where keys are the usernames from /etc/passwd and values were the full ASCII lines from /etc/passwd, same goes for passwd.byuid, group.byname, and so on. All for fast indicing, so that the network server didn't have to repeatedly parse /etc/passwd.