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Full Discussion: Tool to simulate non-sequential disk I/O (simulate db file sequential read) in C POSIX
Top Forums Programming Tool to simulate non-sequential disk I/O (simulate db file sequential read) in C POSIX Post 302531294 by vrghost on Thursday 16th of June 2011 10:25:46 AM
Old 06-16-2011
Tool to simulate non-sequential disk I/O (simulate db file sequential read) in C POSIX
Writing a Tool to simulate non-sequential disk I/O (simulate db file sequential read) in C POSIX

I have over the years come across the same issue a couple of times, and it normally is that the read speed on SAN is absolutely atrocious when doing non-sequential I/O to the disks. Problem being of course that most databases will be doing non-sequential I/O to disks, databases most common read process is db file sequential reads, which would not cause a sequential read of the actual blocks on the device.

My second issue is that it is normally tricky to segregate the different processes enough to be able to clearly test or even show the exact issue with the non-sequential reads and writes, so I end up in very lengthy discussions about possibilities of changing computing theory rather than actually changing the SAN to be able to handle these type of requests, and while that allows for very creative use of similes it is not very efficient use of my time, and I really have little need for more overtime.

So my thought was, how would one go about writing a utility that takes a file that opens a large file and read random blocks of data throughout the file, that way simulating the same effect in a controlled environment.

The general layout I was thinking is

Input for program

name [file to read] [block size] [number of reads]

set block size
set number of reads

get file size

open file

for I << number of reads
set random block address
read random block address from file

close


My problem is, how would I go about reading a random block address from a file.
And is there any way to get the time in milliseconds the operation took

And the POSIX bit, basically the systems I need to use this code on are locked down pretty heavily, and installing a new compiler is a couple of months worth of work, so I want a tool that will be able to be compiled on almost any old compiler.
 

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LEARN ABOUT DEBIAN

space

space(2rheolef) 						    rheolef-6.1 						   space(2rheolef)

NAME

       space -- piecewise polynomial finite element space

DESCRIPTION

       The space class contains some numbering for unknowns and blocked degrees of freedoms related to a given mesh and polynomial approximation.

SYNOPSIS

	   space Q (omega, "P1");
	   space V (omega, "P2", "vector");
	   space T (omega, "P1d", "tensor");

PRODUCT

	   space X = T*V*Q;
	   space Q2 = pow(Q,2);

IMPLEMENTATION

       template <class T>
       class space_basic<T,sequential> : public smart_pointer<space_rep<T,sequential> > {
       public:

       // typedefs:

	   typedef space_rep<T,sequential>   rep;
	   typedef smart_pointer<rep>	     base;
	   typedef typename rep::size_type   size_type;
	   typedef typename rep::valued_type valued_type;

       // allocators:

	   space_basic (const geo_basic<T,sequential>& omega = (geo_basic<T,sequential>()),
			 std::string approx = "", std::string valued = "scalar");
	   space_basic (const space_mult_list<T,sequential>& expr);
	   space_basic (const space_constitution<T,sequential>& constit);

       // accessors:

	   void block  (std::string dom_name);
	   void unblock(std::string dom_name);
	   void block  (const domain_indirect_basic<sequential>& dom);
	   void unblock(const domain_indirect_basic<sequential>& dom);

	   const distributor&  ownership() const;
	   const communicator& comm() const;
	   size_type	       ndof() const;
	   size_type	       dis_ndof() const;

	   const geo_basic<T,sequential>& get_geo() const;
	   const numbering<T,sequential>& get_numbering() const;
	   size_type size() const;
	   valued_type		 valued_tag()	const;
	   const std::string&	 valued()	const;
	   space_component<T,sequential>       operator[] (size_type i_comp);
	   space_component_const<T,sequential> operator[] (size_type i_comp) const;
	   const space_constitution<T,sequential>& get_constitution() const;
	   size_type degree() const;
	   std::string get_approx() const;
	   std::string stamp() const;

	   void dis_idof (const geo_element& K, std::vector<size_type>& dis_idof) const;

	   const distributor& iu_ownership() const;
	   const distributor& ib_ownership() const;

	   bool      is_blocked (size_type     idof) const;
	   size_type	    iub (size_type     idof) const;
	   bool  dis_is_blocked (size_type dis_idof) const;
	   size_type	dis_iub (size_type dis_idof) const;

	   const distributor& ios_ownership() const;
	   size_type idof2ios_dis_idof (size_type idof) const;
	   size_type ios_idof2dis_idof (size_type ios_idof) const;

	   const point_basic<T>& xdof (size_type idof) const;
	   const array<point_basic<T>,sequential>& get_xdofs() const;

	   template <class Function>
	   T momentum (Function f, size_type idof) const;

	   template <class Function>
	   point_basic<T> vector_momentum (Function f, size_type idof) const;

	   array<size_type, sequential> build_indirect_array (
	       const space_basic<T,sequential>& Wh, const std::string& dom_name) const;

	   array<size_type, sequential> build_indirect_array (
	       const space_basic<T,sequential>& Wh, const geo_basic<T,sequential>& bgd_gamma) const;

	   const std::set<size_type>& ext_iu_set() const { return base::data().ext_iu_set(); }
	   const std::set<size_type>& ext_ib_set() const { return base::data().ext_ib_set(); }

       // comparator:

	   bool operator== (const space_basic<T,sequential>& V2) const { return base::data().operator==(V2.data()); }
	   bool operator!= (const space_basic<T,sequential>& V2) const { return ! operator== (V2); }
	   friend bool are_compatible (const space_basic<T,sequential>& V1, const space_basic<T,sequential>& V2) {
	       return are_compatible (V1.data(), V2.data()); }
       };

IMPLEMENTATION

       template <class T>
       class space_basic<T,distributed> : public smart_pointer<space_rep<T,distributed> > {
       public:

       // typedefs:

	   typedef space_rep<T,distributed>  rep;
	   typedef smart_pointer<rep>	     base;
	   typedef typename rep::size_type   size_type;
	   typedef typename rep::valued_type valued_type;

       // allocators:

	   space_basic (const geo_basic<T,distributed>& omega = (geo_basic<T,distributed>()),
			 std::string approx = "", std::string valued = "scalar");
	   space_basic (const space_mult_list<T,distributed>&);
	   space_basic (const space_constitution<T,distributed>& constit);

       // accessors:

	   void block  (std::string dom_name);
	   void unblock(std::string dom_name);
	   void block  (const domain_indirect_basic<distributed>& dom);
	   void unblock(const domain_indirect_basic<distributed>& dom);

	   const distributor&  ownership() const;
	   const communicator& comm() const;
	   size_type	       ndof() const;
	   size_type	       dis_ndof() const;

	   const geo_basic<T,distributed>& get_geo() const;
	   const numbering<T,distributed>& get_numbering() const;
	   size_type size() const;
	   valued_type		 valued_tag()	const;
	   const std::string&	 valued()	const;
	   space_component<T,distributed>	operator[] (size_type i_comp);
	   space_component_const<T,distributed> operator[] (size_type i_comp) const;
	   const space_constitution<T,distributed>& get_constitution() const;
	   size_type degree() const;
	   std::string get_approx() const;
	   std::string stamp() const;

	   void dis_idof (const geo_element& K, std::vector<size_type>& dis_idof) const;

	   const distributor& iu_ownership() const;
	   const distributor& ib_ownership() const;

	   bool      is_blocked (size_type     idof) const;
	   size_type	    iub (size_type     idof) const;

	   bool  dis_is_blocked (size_type dis_idof) const;
	   size_type	dis_iub (size_type dis_idof) const;

	   const distributor& ios_ownership() const;
	   size_type idof2ios_dis_idof (size_type idof) const;
	   size_type ios_idof2dis_idof (size_type ios_idof) const;

	   const point_basic<T>& xdof (size_type idof) const;
	   const array<point_basic<T>,distributed>& get_xdofs() const;

	   template <class Function>
	   T momentum (Function f, size_type idof) const;

	   template <class Function>
	   point_basic<T> vector_momentum (Function f, size_type idof) const;

	   array<size_type, distributed> build_indirect_array (
	       const space_basic<T,distributed>& Wh, const std::string& dom_name) const;

	   array<size_type, distributed> build_indirect_array (
	       const space_basic<T,distributed>& Wh, const geo_basic<T,distributed>& bgd_gamma) const;

	   const std::set<size_type>& ext_iu_set() const { return base::data().ext_iu_set(); }
	   const std::set<size_type>& ext_ib_set() const { return base::data().ext_ib_set(); }

       // comparator:

	   bool operator== (const space_basic<T,distributed>& V2) const { return base::data().operator==(V2.data()); }
	   bool operator!= (const space_basic<T,distributed>& V2) const { return ! operator== (V2); }
	   friend bool are_compatible (const space_basic<T,distributed>& V1, const space_basic<T,distributed>& V2) {
	       return are_compatible (V1.data(), V2.data()); }
       };

rheolef-6.1							    rheolef-6.1 						   space(2rheolef)
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