Should I Dispose() DataSet and DataTable? - datatable

Question

DataSet and DataTable both implement IDisposable, so, by conventional best practices, I should call their Dispose() methods.
However, from what I've read so far, DataSet and DataTable don't actually have any unmanaged resources, so Dispose() doesn't actually do much.
Plus, I can't just use using(DataSet myDataSet...) because DataSet has a collection of DataTables.
So, to be safe, I'd need to iterate through myDataSet.Tables, dispose of each of the DataTables, then dispose of the DataSet.
So, is it worth the hassle to call Dispose() on all of my DataSets and DataTables?
Addendum:
For those of you who think that DataSet should be disposed:
In general, the pattern for disposing is to use using or try..finally, because you want to guarantee that Dispose() will be called.
However, this gets ugly real fast for a collection. For example, what do you do if one of the calls to Dispose() thrown an exception? Do you swallow it (which is "bad") so that you can continue on to dispose the next element?
Or, do you suggest that I just call myDataSet.Dispose(), and forget about disposing the DataTables in myDataSet.Tables?

Answer 1

Here are a couple of discussions explaining why Dispose is not necessary for a DataSet.
To Dispose or Not to Dispose ?:
The Dispose method in DataSet exists ONLY because of side effect of inheritance-- in other words, it doesn't actually do anything useful in the finalization.
Should Dispose be called on DataTable and DataSet objects? includes some explanation from an MVP:
The system.data namespace (ADONET) does not contain
unmanaged resources. Therefore there is no need to dispose any of those as
long as you have not added yourself something special to it.
Understanding the Dispose method and datasets? has a with comment from authority Scott Allen:
In pratice we rarely Dispose a DataSet because it offers little benefit"
So, the consensus there is that there is currently no good reason to call Dispose on a DataSet.

Answer 2

Update (December 1, 2009):
I'd like to amend this answer and concede that the original answer was flawed.
The original analysis does apply to objects that require finalization – and the point that practices shouldn’t be accepted on the surface without an accurate, in-depth understanding still stands.
However, it turns out that DataSets, DataViews, DataTables suppress finalization in their constructors – this is why calling Dispose() on them explicitly does nothing.
Presumably, this happens because they don’t have unmanaged resources; so despite the fact that MarshalByValueComponent makes allowances for unmanaged resources, these particular implementations don’t have the need and can therefore forgo finalization.
(That .NET authors would take care to suppress finalization on the very types that normally occupy the most memory speaks to the importance of this practice in general for finalizable types.)
Notwithstanding, that these details are still under-documented since the inception of the .NET Framework (almost 8 years ago) is pretty surprising (that you’re essentially left to your own devices to sift though conflicting, ambiguous material to put the pieces together is frustrating at times but does provide a more complete understanding of the framework we rely on everyday).
After lots of reading, here’s my understanding:
If an object requires finalization, it could occupy memory longer than it needs to – here’s why: a) Any type that defines a destructor (or inherits from a type that defines a destructor) is considered finalizable; b) On allocation (before the constructor runs), a pointer is placed on the Finalization queue; c) A finalizable object normally requires 2 collections to be reclaimed (instead of the standard 1); d) Suppressing finalization doesn’t remove an object from the finalization queue (as reported by !FinalizeQueue in SOS)
This command is misleading; Knowing what objects are on the finalization queue (in and of itself) isn’t helpful; Knowing what objects are on the finalization queue and still require finalization would be helpful (is there a command for this?)
Suppressing finalization turns a bit off in the object's header indicating to the runtime that it doesn’t need to have its Finalizer invoked (doesn’t need to move the FReachable queue); It remains on the Finalization queue (and continues to be reported by !FinalizeQueue in SOS)
The DataTable, DataSet, DataView classes are all rooted at MarshalByValueComponent, a finalizable object that can (potentially) handle unmanaged resources
Because DataTable, DataSet, DataView don’t introduce unmanaged resources, they suppress finalization in their constructors
While this is an unusual pattern, it frees the caller from having to worry about calling Dispose after use
This, and the fact that DataTables can potentially be shared across different DataSets, is likely why DataSets don’t care to dispose child DataTables
This also means that these objects will appear under the !FinalizeQueue in SOS
However, these objects should still be reclaimable after a single collection, like their non-finalizable counterparts
4 (new references):
http://www.devnewsgroups.net/dotnetframework/t19821-finalize-queue-windbg-sos.aspx
http://blogs.msdn.com/tom/archive/2008/04/28/asp-net-tips-looking-at-the-finalization-queue.aspx
http://issuu.com/arifaat/docs/asp_net_3.5unleashed
http://msdn.microsoft.com/en-us/magazine/bb985013.aspx
http://blogs.msdn.com/tess/archive/2006/03/27/561715.aspx
Original Answer:
There are a lot of misleading and generally very poor answers on this - anyone who's landed here should ignore the noise and read the references below carefully.
Without a doubt, Dispose should be called on any Finalizable objects.
DataTables are Finalizable.
Calling Dispose significantly speeds up the reclaiming of memory.
MarshalByValueComponent calls GC.SuppressFinalize(this) in its Dispose() - skipping this means having to wait for dozens if not hundreds of Gen0 collections before memory is reclaimed:
With this basic understanding of finalization we
can already deduce some very important
things:
First, objects that need finalization
live longer than objects that do not.
In fact, they can live a lot longer.
For instance, suppose an object that
is in gen2 needs to be finalized.
Finalization will be scheduled but the
object is still in gen2, so it will
not be re-collected until the next
gen2 collection happens. That could be
a very long time indeed, and, in fact,
if things are going well it will be a
long time, because gen2 collections
are costly and thus we want them to
happen very infrequently. Older
objects needing finalization might
have to wait for dozens if not
hundreds of gen0 collections before
their space is reclaimed.
Second, objects that need finalization
cause collateral damage. Since the
internal object pointers must remain
valid, not only will the objects
directly needing finalization linger
in memory but everything the object
refers to, directly and indirectly,
will also remain in memory. If a huge
tree of objects was anchored by a
single object that required
finalization, then the entire tree
would linger, potentially for a long
time as we just discussed. It is
therefore important to use finalizers
sparingly and place them on objects
that have as few internal object
pointers as possible. In the tree
example I just gave, you can easily
avoid the problem by moving the
resources in need of finalization to a
separate object and keeping a
reference to that object in the root
of the tree. With that modest change
only the one object (hopefully a nice
small object) would linger and the
finalization cost is minimized.
Finally, objects needing finalization
create work for the finalizer thread.
If your finalization process is a
complex one, the one and only
finalizer thread will be spending a
lot of time performing those steps,
which can cause a backlog of work and
therefore cause more objects to linger
waiting for finalization. Therefore,
it is vitally important that
finalizers do as little work as
possible. Remember also that although
all object pointers remain valid
during finalization, it might be the
case that those pointers lead to
objects that have already been
finalized and might therefore be less
than useful. It is generally safest to
avoid following object pointers in
finalization code even though the
pointers are valid. A safe, short
finalization code path is the best.
Take it from someone who's seen 100s of MBs of non-referenced DataTables in Gen2: this is hugely important and completely missed by the answers on this thread.
References:
1 -
http://msdn.microsoft.com/en-us/library/ms973837.aspx
2 -
http://vineetgupta.spaces.live.com/blog/cns!8DE4BDC896BEE1AD!1104.entry
http://www.dotnetfunda.com/articles/article524-net-best-practice-no-2-improve-garbage-collector-performance-using-finalizedispose-pattern.aspx
3 -
http://codeidol.com/csharp/net-framework/Inside-the-CLR/Automatic-Memory-Management/

Answer 3

You should assume it does something useful and call Dispose even if it does nothing in current .NET Framework incarnations. There's no guarantee it will stay that way in future versions leading to inefficient resource usage.

Answer 4

Even if an object has no unmanaged resources, disposing might help GC by breaking object graphs. In general, if an object implements IDisposable, Dispose() should be called.
Whether Dispose() actually does something or not depends on the given class. In case of DataSet, Dispose() implementation is inherited from MarshalByValueComponent. It removes itself from container and calls Disposed event. The source code is below (disassembled with .NET Reflector):
protected virtual void Dispose(bool disposing)
{
if (disposing)
{
lock (this)
{
if ((this.site != null) && (this.site.Container != null))
{
this.site.Container.Remove(this);
}
if (this.events != null)
{
EventHandler handler = (EventHandler) this.events[EventDisposed];
if (handler != null)
{
handler(this, EventArgs.Empty);
}
}
}
}
}

Answer 5

Do you create the DataTables yourself? Because iterating through the children of any Object (as in DataSet.Tables) is usually not needed, as it's the job of the Parent to dispose all its child members.
Generally, the rule is: If you created it and it implements IDisposable, Dispose it. If you did NOT create it, then do NOT dispose it, that's the job of the parent object. But each object may have special rules, check the Documentation.
For .NET 3.5, it explicitly says "Dispose it when not using anymore", so that's what I would do.

Answer 6

I call dispose anytime an object implements IDisposeable. It's there for a reason.
DataSets can be huge memory hogs. The sooner they can be marked for clean up, the better.
update
It's been 5 years since I answered this question. I still agree with my answer. If there is a dispose method, it should be called when you are done with the object. The IDispose interface was implemented for a reason.

Answer 7

If your intention or the context of this question is really garbage collection, then you can set the datasets and datatables to null explicitly or use the keyword using and let them go out of scope. Dispose does not do much as Tetraneutron said it earlier. GC will collect dataset objects that are no longer referenced and also those that are out of scope.
I really wish SO forced people down voting to actually write a comment before downvoting the answer.

Answer 8

Datasets implement IDisposable thorough MarshalByValueComponent, which implements IDisposable. Since datasets are managed there is no real benefit to calling dispose.

Answer 9

Try to use Clear() function.
It works great for me for disposing.
DataTable dt = GetDataSchema();
//populate dt, do whatever...
dt.Clear();

Answer 10

No need to Dispose()
because DataSet inherit MarshalByValueComponent class and MarshalByValueComponent implement IDisposable Interface

Answer 11

This is the right way to properly Dispose the DataTable.
private DataTable CreateSchema_Table()
{
DataTable td = null;
try
{
td = new DataTable();
//use table DataTable here
return td.Copy();
}
catch { }
finally
{
if (td != null)
{
td.Constraints.Clear();
td.Clear();
td.Dispose();
td = null;
}
}
}

Answer 12

And this can be the best/proper way to Dispose and release the memory consumed by DataSet.
try
{
DataSet ds = new DataSet("DS");
//use table DataTable here
}
catch { }
finally
{
if (ds != null)
{
ds.EnforceConstraints = false;
ds.Relations.Clear();
int totalCount = ds.Tables.Count;
for (int i = totalCount - 1; i >= 0; i--)
{
DataTable td1 = ds.Tables[i];
if (td1 != null)
{
td1.Constraints.Clear();
td1.Clear();
td1.Dispose();
td1 = null;
}
}
ds.Tables.Clear();
ds.Dispose();
ds = null;
}
}