Out of memory exception when there are plenty of memories in 64 bit system

I make a program.

Part of the program is to set the "differences" between 2 large text files.

The files aren't really that large. Like 10 million lines.

I save them on a hashtable. Again I only save the long hash.

Code:

---

    Private Sub createMD5HashFromFileTheLoop(ByVal fileToWrite As String, ByVal fileToRead As String, ByRef ExisingHashSet As Generic.HashSet(Of Int64), appending As Boolean, ByVal actuallyWrite As Boolean)
        Using sr As New System.IO.StreamReader(fileToRead)
            Using sw As New System.IO.StreamWriter(fileToWrite, appending, defaultEncoding)
                While Not sr.EndOfStream
                    'Dim offset = sr.BaseStream.Position

                    'Dim nextOffset = sr.BaseStream.Position
                    Dim l As String = sr.ReadLine()
                    Dim hashmd5long = compute64bitHash(l)
                    Do ' a trick to put the for each in a "nest" that we can exit from
                        If ExisingHashSet.Contains(hashmd5long) Then
                            Exit Do
                        Else
                            ExisingHashSet.Add(hashmd5long)
                        End If
                        'hashSet.Item(hashmd5long).Add(offset)
                        If actuallyWrite Then
                            sw.WriteLine(l)
                        End If
                    Loop While False
                    'sr.BaseStream.Position = nextOffset
                    System.Windows.Forms.Application.DoEvents()
                End While
            End Using
        End Using
    End Sub

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The computer, and the system, and the program is all 64 bits.

The size of ExisingHashSet is 2893249 when error occurs. Each entry takes a long (4 bytes) so we're talking about 8-10 mb memory at most. Far less than 8 GB ram and virtual memories.

Taskmanager do not work and I got another windows telling I do ran out of memory. I also run mongodb on that same computer.

However I never got out of memory problem without running this program and this program used to run fine. I just wonder how those hastable took so much memory.

Is there a particular reason you need it all in memory right now? Just wondering.


EDIT: This might be a good explanation as to why you're getting an OOM exception despite having enough room physically.

Quote:

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Originally Posted by teguh123

Each entry takes a long (4 bytes)

---

A Long is 8 bytes not 4.

I'm curious. Does your program at the time of the error hold any references to other large objects like arrays, dictionaries or lists ?