sendmail, 4th Edition

btree

The db(3) form of database V8.1 and later

The term btree stands for “balanced tree.” It is a grow-only form of database. Lookups and insertions are fast, but deletions do not shrink the size of the database file.^[343] A good description of this form of database can be found in The Art of Computer Programming, Vol. 3: Sorting and Searching, by D.E. Knuth. The btree type is available only if sendmail was compiled with NEWDB defined and the Berkeley or Sleepycat db library linked (The Sleepycat DB Library on page 104). In most cases, the hash type (hash on page 908) will perform slightly better.

Quite a few database switches are available with this database-map type. They are listed in Table 23-7.

Table 23-7. The btree database-map type K command switches

Switch	§	Description
-A	-A on page 886	Append values for duplicate keys.
-a	-a on page 887	Append tag on successful match.
-D	-D on page 887	Don’t use this database map if DeliveryMode=defer.
-f	-f on page 887	Don’t fold keys to lowercase.
-m	-m on page 888	Suppress replacement on match.
-N	-N on page 889	Append a null byte to all keys.
-O	-O on page 889	Never add a null byte.
-o	-o on page 889	The database map is optional.
-q	-q on page 889	Don’t strip quotes from key.
-S	-S on page 890	Space replacement character.
-T	-T on page 890	Suffix to append on temporary failure.
-t	-t on page 891	Ignore temporary errors.

One use for this btree type might be to look up users for whom permission to ...