Database Commands
The database commands provide a conduit into the DB method functions.
They are all fairly straightforward and I describe them in terms of their
DB functions briefly here, with a link to the DB page where appropriate.
The first set of commands are those I believe will be the primary functions
used by most databases. Some are directly related to their DB counterparts,
and some are higher level functions that are useful to provide the user.
> berkdb open [-env env]
[-btree|-hash|-recno|-queue|-unknown]
[-create] [-excl] [-nommap] [-rdonly] [-truncate]
[-mode
mode] [-errfile filename]
[-dup] [-dupsort] [-recnum] [-renumber] [-revsplitoff]
[-snapshot] [-upgrade]
[-ffactor density]
[-nelem size]
[-lorder order]
[-delim delim]
[-len len]
[-pad pad]
[-source file]
[-minkey minkey]
[-cachesize {gbytes bytes ncaches}]
[-pagesize pagesize]
[--]
[filename [subdbname]]
This command will invoke the db_create
function. If the command is given the -env option, then we
will accordingly creating the database within the context of that environment.
After it successfully gets a handle to a database, we bind it to a new
Tcl command of the form dbX, where X is an integer starting
at 0 (e.g. db0, db1, etc). We use the Tcl_CreateObjCommand()
to create the top level database function. It is through this handle
that the user can access all of the commands described in the Database
Commands section. Internally, the database handle is sent as
the ClientData portion of the new command set so that all future
database calls access the appropriate handle.
After parsing all of the optional arguments affecting the setup of the
database and making the appropriate calls to DB to manipulate those values,
we open the database for the user. It translates to the
DB->open
method call after parsing all of the various optional arguments.
We automatically set the DB_THREAD flag. The arguments are:
-
-- - Terminate the list of options and use remaining arguments as
the file or subdb names (thus allowing the use of filenames beginning with
a dash '-')
-
-btree - DB_BTREE database
-
-hash - DB_HASH database
-
-recno - DB_RECNO database
-
-queue - DB_QUEUE database
-
-create selects the DB_CREATE flag to create underlying files
-
-excl selects the DB_EXCL flag to exclusively create underlying
files
-
-nommap selects the DB_NOMMAP flag to forbid mmaping of files
-
-rdonly selects the DB_RDONLY flag for opening in read-only mode
-
-truncate selects the DB_TRUNCATE flag to truncate the database
-
-mode mode specifies the mode for created files
-
-errfile specifies the error file to use for this environment to
filename
by calling DB->set_errfile.
If
the file already exists then we will append to the end of the file
-
-dup selects the DB_DUP flag to permit duplicates in the database
-
-dupsort selects the DB_DUPSORT flag to support sorted duplicates
-
-recnum selects the DB_RECNUM flag to support record numbers in
btrees
-
-renumber selects the DB_RENUMBER flag to support mutable record
numbers
-
-revsplitoff selects the DB_REVSPLITOFF flag to suppress reverse
splitting of pages on deletion
-
-snapshot selects the DB_SNAPSHOT flag to support database snapshots
-
-upgrade selects upgrading databases using the DB->upgrade
method
-
-ffactor sets the hash table key density to the given density
using
the DB->set_h_ffactor
method
-
-nelem sets the hash table size estimate to the given size
using
the DB->set_h_nelem method
-
-lorder sets the byte order for integers stored in the database
meta-data to the given order using the DB->set_lorder
method
-
-delim sets the delimiting byte for variable length records to
delim
using the DB->set_re_delim
method
-
-len sets the length of fixed-length records to len
using the DB->set_re_len
method
-
-pad sets the pad character used for fixed length records to
pad
using the DB->set_re_pad method
-
-source sets the backing source file name to file
using the DB->set_re_source
method
-
-minkey sets the minimum number of keys per Btree page to minkey
using the DB->set_bt_minkey
method
-
-cachesize sets the size of the database cache to the size
specified by gbytes and bytes, broken up into
ncaches
number of caches using the DB->set_cachesize
method
-
-pagesize sets the size of the database page to pagesize using
the DB->set_pagesize method
-
filename indicates the name of the database
-
subdbname indicate the name of the sub-database