Release 2.0: converting applications
Mapping the Berkeley DB 1.85 functionality into Berkeley DB version 2 is almost always
simple. The manual page DB->open() replaces the Berkeley DB 1.85 manual
pages dbopen(3), btree(3), hash(3) and
recno(3). You should be able to convert each 1.85 function
call into a Berkeley DB version 2 function call using just the DB->open()
documentation.
Some guidelines and things to watch out for:
- Most access method functions have exactly the same semantics as in Berkeley DB
1.85, although the arguments to the functions have changed in some cases.
To get your code to compile, the most common change is to add the
transaction ID as an argument (NULL, since Berkeley DB 1.85 did not support
transactions.)
- You must always initialize DBT structures to zero before using them with
any Berkeley DB version 2 function. (They do not normally have to be
reinitialized each time, only when they are first allocated. Do this by
declaring the DBT structure external or static, or by calling the C
library routine
bzero(3) or memset(3).)
- The error returns are completely different in the two versions. In Berkeley DB
1.85, < 0 meant an error, and > 0 meant a minor Berkeley DB exception.
In Berkeley DB 2.0, > 0 means an error (the Berkeley DB version 2 functions
return
errno on error) and < 0 means a Berkeley DB exception.
See Error returns to applications
for more information.
- The Berkeley DB 1.85 DB->seq function has been replaced by cursors in Berkeley DB
version 2. The semantics are approximately the same, but cursors require
the creation of an extra object (the DBC object), which is then used to
access the database.
Specifically, the partial key match and range search functionality of the
R_CURSOR flag in DB->seq has been replaced by the DB_SET_RANGE flag in
DBC->get().
- In version 2 of the Berkeley DB library, additions or deletions into Recno
(fixed and variable-length record) databases no longer automatically
logically renumber all records after the add/delete point, by default.
The default behavior is that deleting records does not cause subsequent
records to be renumbered, and it is an error to attempt to add new records
between records already in the database. Applications wanting the
historic Recno access method semantics should call the
DB->set_flags() method with the DB_RENUMBER flag.
- Opening a database in Berkeley DB version 2 is a much heavier-weight operation
than it was in Berkeley DB 1.85. Therefore, if your historic applications were
written to open a database, perform a single operation, and close the
database, you may observe performance degradation. In most cases, this
is due to the expense of creating the environment upon each open. While
we encourage restructuring your application to avoid repeated opens and
closes, you can probably recover most of the lost performance by simply
using a persistent environment across invocations.
While simply converting Berkeley DB 1.85 function calls to Berkeley DB version 2
function calls will work, we recommend that you eventually reconsider your
application's interface to the Berkeley DB database library in light of the
additional functionality supplied by Berkeley DB version 2, as it is likely to
result in enhanced application performance.