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Tool to simulate non-sequential disk I/O (simulate db file sequential read) in C POSIX

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Top Forums Programming Tool to simulate non-sequential disk I/O (simulate db file sequential read) in C POSIX
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Old 06-18-2011
Happy with it not being completely random, as long as it jumps around enough to not catch itself on the read advance routines when running on the SAN, and as simulation goes, the database would more than likely read specific files or parts of files more than others anyway.

Here comes my next exciting problem, a database will only read a certain amount of time, other bits are sorting, writing and whatever else the database gets up to. So I am thinking of adding how manny cycles there are between reads, because just doing random reads and nothing else is giving rather silly results. In its purest form I seem to be able to get 100% WaitI/O and read about 6-12 Kb/s, which is pretty impressive in its ow right.

And todays exiting question, anyone feel like guessing how many cycles in a million that a rather streamlined database spends reading disk dataSmilie
Anyone who guesses the right answer wins an icecream, collectable in Camden, London (U.K.)

/Ben
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LEARN ABOUT HPUX

prealloc

prealloc(2)							System Calls Manual						       prealloc(2)

NAME

       prealloc - preallocate fast disk storage

SYNOPSIS

DESCRIPTION

       is used to preallocate space on a disk for faster storage operations.

       fildes  is  a  file  descriptor obtained from a or system call for an ordinary file of zero length.  It must be opened writable, because it
       will be written to by size is the size in bytes to be preallocated for the file specified by fildes.  At least size  bytes  will  be  allo-
       cated.	Space  is  allocated  in an implementation-dependent fashion for fast sequential reads and writes.  The EOF in an extended file is
       left at the end of the preallocated area.  The current file pointer is left at zero.  The file is zero-filled.

       Using on a file does not give the file an attribute that is inherited when copying or restoring the file using a program such  as  or  (see
       cp(1)  and  tar(1)).  It simply ensures that disk space has been preallocated for size bytes in a manner suited for sequential access.  The
       file can be extended beyond these limits by operations past the original end of file.  However, this space will not  necessarily  be  allo-
       cated using any special strategy.

RETURN VALUE

       Upon successful completion, returns 0; otherwise, it returns -1 and sets to indicate the error.

ERRORS

       fails and no disk space is allocated if any of the following conditions are encountered:

	      [EBADF]	     fildes is not a valid open file descriptor opened for writing.

	      [EDQUOT]	     User's disk quota block limit has been reached for this file system.

	      [EFBIG]	     size exceeds the maximum file size or the process's file size limit.  See ulimit(2).

	      [ENOSPC]	     Not enough space is left on the device to allocate the requested amount; no space was allocated.

	      [ENOTEMPTY]      fildes not associated with an ordinary file of zero length.

EXAMPLES

       Assuming  a process has opened a file for writing, the following call to preallocates at least 50000 bytes on disk for the file represented
       by file descriptor outfd:

WARNINGS

       Allocation of the file space is highly dependent on current disk usage.	A successful return does not tell  you	how  fragmented  the  file
       actually might be if the disk is nearing its capacity.

AUTHOR

       was developed by HP.

SEE ALSO

       prealloc(1), creat(2), dup(2), fcntl(2), open(2), prealloc64(2), read(2), ulimit(2), write(2).

																       prealloc(2)