Should I Dispose DataSet and 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

User · Answer

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

User · Answer

Try to use Clear   function   It works great for me for disposing   DataTable dt   GetDataSchema      populate dt  do whatever    dt Clear

User · Answer

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

User · Answer

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  quot Dispose it when not using anymore quot   so that s what I would do

User · Answer

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   amp  amp   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

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

And this can be the best proper way to Dispose and release the memory consumed by DataSet  try               DataSet ds   new DataSet  quot DS quot              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  gt   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

User · Answer

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

User · Answer

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

User · Answer

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

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