svn commit: r1622566 - /jena/site/trunk/content/documentation/tdb/faqs.mdtext

[an...@apache.org]

Author: andy
Date: Thu Sep  4 21:28:42 2014
New Revision: 1622566

URL: http://svn.apache.org/r1622566
Log:
MSWindows and database delete

Modified:
    jena/site/trunk/content/documentation/tdb/faqs.mdtext

Modified: jena/site/trunk/content/documentation/tdb/faqs.mdtext
URL: http://svn.apache.org/viewvc/jena/site/trunk/content/documentation/tdb/faqs.mdtext?rev=1622566&r1=1622565&r2=1622566&view=diff
==============================================================================
--- jena/site/trunk/content/documentation/tdb/faqs.mdtext (original)
+++ jena/site/trunk/content/documentation/tdb/faqs.mdtext Thu Sep  4 21:28:42 2014
@@ -11,6 +11,7 @@ Title: TDB FAQs
 -   [Should I use a SSD?](#ssd)
 -   [Why do I get the exception *Can't open database at location /path/to/db as it is already locked by the process with PID 1234* when trying to open a TDB database?](#lock-exception)
 -   [I see a warning that *Location /path/to/db was not locked, if another JVM accessed this location simultaneously data corruption may have occurred* in my logs?](#no-lock-warning)
+-   [Why can't I delete a dataset (MS Windows/64 bit)?](#windows-dataset-delete)
 
 <a name="transactions"></a>
 ## Does TDB support transactions?
@@ -148,4 +149,22 @@ This warning can occur in rare circumsta
 database was eligible to be locked but wasn't.  This can usually only occur if you circumvented the normal TDB database opening procedures somehow.
 
 As the warning states data corruption may occur if another JVM accesses the location while your process is accessing it.  Ideally you should follow the
-advice on [multi-JVM usage](#multi-jvm) if this might happen, otherwise the warning can likely be safely ignored.
\ No newline at end of file
+advice on [multi-JVM usage](#multi-jvm) if this might happen, otherwise the warning can likely be safely ignored.
+
+## Deleting Datasets on MS Windows {#windows-dataset-delete}
+
+Java on MS Windows does not provide the ability to delete a memory mapped
+file while the JVM is still running.  The file is properly deleted when the
+JVM exits.  This is a known issue with Java.  
+See the Java bug database e.g. 
+[Bug id: 4724038](http://bugs.java.com/view_bug.do?bug_id=4724038) and several
+others. While there are some workarounds mentioned on the web, 
+none is known to always work on all JVMs.
+
+On 64 bit systems, TDB uses memory mapped to manage datasets on disk.  This
+means that the operating system dynamically controls how much of a file is held in
+RAM, trading off against requests by other applications.  But it also means
+the database files are not properly deleted until the JVM exits.  A new
+dataset can not be created in the same location (directory on disk).
+
+The workaround is to use a different location.