This Tcl command is used to open a storage. It takes one, two or three
arguments:
The rest of the arguments are alternating option names and values.
The following options are supported:
- -driver driver-name. The driver
name defaults to "Metakit 2.4".
- -rwmode mode. The read-write mode defaults to "rw" which
means the storage is opened for reading and writing.
- -commitatclose bool. If true, the storage is committed
before closing it if there are any changes. The default setting is true.
- -opengc bool. If true, a garbage collection is performed
when the storage is first opened, to recycle any remaining unreachable
space. The default setting is true.
- -gcbeforecommit bool. If true, a garbage collection is
performed before each commit. The default setting is true.
- -autogc bool. If true, a garbage collection is performed
whenever the tgraph system determines that one or more nodes or
vertices have become unreachable. The default setting is true. If many
changes are applied to a storage over a short period of time, it is
advantageous to delay garbage collection until all changes have been
applied. Setting -autogc to false implements this option.
- -bigprealloc bool. If true, the tgraph system preallocates
many nodes and vertices so that many new nodes and vertices can be
created efficiently. The default setting is false, which means that
fewer nodes and vertices are preallocated. This is a space-time
tradeoff. When many new vertices and nodes are added to a storage over
a short period of time, it is advantageous to set this option to true,
so that the library efficiently preallocates space for many new
entities.
- -compactatclose bool. If true, the tgraph library compacts
the storage as much as possible while preserving its logical
structure, when the storage is closed. This results in a smaller disk
file or database. The default setting is false, which means that when
the storage is closed, no compaction takes place. This is a space-time
tradeoff. It might be advantageous to set this option to true for
storages from which a large number of entities have been removed.
The tgraph::open command returns a Tcl object representing the
new storage just opened. If a storage is opened multiple times, the same
Tcl object is returned on subsequent calls to tgraph::open. The
Tcl storage object can be used to operate
on the e4Graph storage object.
Here is an example showing how to open an e4Graph storage from Tcl and
save the returned object in a Tcl variable for future use.
set mystorage [tgraph::open foo.db]
