Re: [HACKERS] Supporting huge pages on Windows

From: Amit Kapila [mailto:amit.kapila16@gmail.com]
> Hmm.  It doesn't work even on a command prompt with administrative
> privileges. It gives below error:
> 
> waiting for server to start....2017-01-17 11:20:13.780 IST [4788] FATAL:
> could not create shared memory segment: error code 1450
> 2017-01-17 11:20:13.780 IST [4788] DETAIL:  Failed system call was
> CreateFileMap ping(size=148897792,
> name=Global/PostgreSQL:E:/WorkSpace/PostgreSQL/master/Data)
> .
> 2017-01-17 11:20:13.780 IST [4788] LOG:  database system is shut down
> stopped waiting
> pg_ctl: could not start server
> Examine the log output.
> 
> 
> Now, error code 1450 can occur due to insufficient system resources, so
> I have tried by increasing the size of shared memory (higher value of
> shared_buffers) without your patch and it works.  This indicates some
> problem with the patch.

Hmm, the large-page requires contiguous memory for each page, so this error could occur on a long-running system where
thememory is heavily fragmented.  For example, please see the following page and check the memory with RAMMap program
referredthere.
 

http://blog.dbi-services.com/large-pages-and-memory_target-on-windows/

BTW, is your OS or PostgreSQL 32-bit?


> >  It seems that Windows removes many privileges, including "Lock Pages
> in Memory", when starting the normal command prompt.  As its evidence, you
> can use the attached priv.c to see what privileges are assigned and and
> enabled/disabled.  Build it like "cl priv.c" and just run priv.exe on each
> command prompt.  Those runs show different privileges.
> >
> 
> This is bad.
> 
> > Should I need to do something, e.g. explain in the document that the user
> should use the command prompt with administrative privileges when he uses
> huge_pages?
> >
> 
> I think it is better to document in some way if we decide to go-ahead with
> the patch.

Sure, I added these sentences. 

+        To start the database server on the command prompt as a standalone process,
+        not as a Windows service, run the command prompt as an administrator or
+        disable the User Access Control (UAC). When the UAC is enabled, the normal
+        command prompt revokes the user right Lock Pages in Memory.

Regards
Takayuki Tsunakawa


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