Q & A: I am running on 64 bit and all of my tasks are waiting on SOS_RESERVEDMEMBLOCKLIST, What is going on?

This wait type represents waiting on multi page allocations inside of SQLOS’s memory manager. As you remember from my description of memory manager’s working internals, it has two major allocators single page allocator, SPA and multi page allocator, MPA. Majority of the time SQL Server internal code uses SPA, however in some cases it will…

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Be Aware: 4GB of VAS under WOW, does it really worth it?

By now you have heard a lot about the fact that under WOW a 32 bit process can get 4GB of VAS.   I agree this is great, but I would like you to be aware of something that might hit you really hard.  As it turns out enabling 4GB VAS can be problematic due to…

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Be Aware: VirtualAlloc with MEM_RESERVE can fail even if you have plenty of VAS inside of the process

 Many developers assume that if you have plenty of free VAS in your process VirtualAlloc (http://msdn.microsoft.com/library/default.asp?url=/library/en-us/memory/base/virtualalloc.asp) and VirtualAllocEx (http://msdn.microsoft.com/library/default.asp?url=/library/en-us/memory/base/virtualallocex.asp) calls with MEM_RESERVE parameter can’t fail. This is not actually true.  Remember that when allocating VAS region OS creates VAD (Virtual Address Descriptor). VAD manages VAS region, for more info read http://blogs.msdn.com/slavao/archive/2005/01/27/361678.aspx. When system is low…

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Be Aware: Using AWE, locked pages in memory, on 64 bit

We have already talked about Windows AWE mechanism on 32 bit and how SQL Server utilizes it. Today I would like to go over AWE & related mechanism on 64 bit platforms.   To some people it comes as a surprise that AWE mechanism is still present and actually could be useful on 64 bit…

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Look at Memory Leaks – Classify and Identify

In my previous post I talked about type of Memory Pressures. Today I would like to talk about related subject – Memory Leaks.  Before you continue reading please make sure that you are familiar with how memory is managed on Windows.   Memory leaks are bugs that happen very often. I think it is very…

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Memory Pressure – Classified

So far I touched on subjects that have been widely discussed in the industry. Today I would like to talk about a subject that you would hardly find information about:  memory pressure..  On a surface the subject appears simple but in reality this is not the case.   There are two types of memory pressure…

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A look at Virtual Address Space – VAS

Memory is a set of common resources shared by applications, their components and operating system. One needs to be very specific when referring to a given memory resource. Mistakenly, in many cases, developers, users, DBAs refer to different memory resources using one generic term memory.   This perfectly worked in DOS times when things were simple,…

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