Memory using by a Hashtable object in .Net

Question

We have a web application which is using HttpRuntime Cache for storing frequently using DB data. code snippet is:

public static void Add(string cacheName, Hashtable cacheValue)
{
  System.Web.HttpRuntime.Cache.Add(cacheName, cacheValue, null, DateTime.Now.AddSeconds(60), TimeSpan.Zero, System.Web.Caching.CacheItemPriority.High, null);
}

Here a hashtable object receives data from database and adding to HttpRuntime Cache. How to find out the memory taken by this hashtable object by using code.....Thanks.

possible duplicate of [How to get object size in memory?](http://stackoverflow.com/questions/605621/how-to-get-object-size-in-memory) — Jonathon Reinhart, May 15 '13 at 07:40

animaonline · Accepted Answer · 2013-05-15T08:15:41.240

There is no way to get the size of a managed object, it differs from implementation to implementation.

See this link for more details: Size of a managed object

For an inaccurate estimate you can try using GC.GetTotalMemory(false) just before the HashTable is initialized and right after it is filled with data:

        Console.Write("How many entries would you like to store in the Hashtable?:");

        int hashTableEntries;
        int.TryParse(Console.ReadLine(), out hashTableEntries);

        var memBeforeHashInit = GC.GetTotalMemory(true);

        var hashTable = new Hashtable();

        for (int i = 0; i < hashTableEntries; i++)
            hashTable.Add(i, i);

        var memAfterHashInit = GC.GetTotalMemory(false);

        var diff = memAfterHashInit - memBeforeHashInit;

        Console.WriteLine("Memory used since startup: {0} bytes" +
            "\r\n" +
            "Hashtable entries: {1}" +
            "\r\n" +
            "Press any key to exit", diff, hashTableEntries);
        Console.ReadLine();

As it appears, that once a Hashtable is initialized, 8192 bytes are allocated in memory, it also appears that it allocates memory for 64 of its elements, giving 128 bytes per element. As soon as you add the 65th element to the Hashtable it reserves another 8192 bytes for another 64 elements.

It may differ on another system, it's up to the CLR to decide that :)

Memory using by a Hashtable object in .Net

1 Answers1