06-19-2012
Dealing with a really high amount of reads merged
Quote:
[root@cms_publish content]# cat /sys/block/xvda/stat
720655 296049 40532272 5312020 2567729 5536313 64831540 41190456 0 2004640 46503376
I'm trying to performance tune the I/O of my web server, which is at 41.1% reads merged (If my math is correct), which seems a tad high to just be going along with the defaults. Will modifying read_ahead_kb affect the value of "reads merged" in diskstats? If not, what's a good way of tracking performance progress so I know when I've set read_ahead_kb too high?
Last edited by thmnetwork; 06-19-2012 at 02:56 PM..
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CAT(1) General Commands Manual CAT(1)
NAME
cat - catenate and print
SYNOPSIS
cat [ -u ] [ -n ] [ -s ] [ -v ] file ...
DESCRIPTION
Cat reads each file in sequence and displays it on the standard output. Thus
cat file
displays the file on the standard output, and
cat file1 file2 >file3
concatenates the first two files and places the result on the third.
If no input file is given, or if the argument `-' is encountered, cat reads from the standard input file. Output is buffered in the block
size recommended by stat(2) unless the standard output is a terminal, when it is line buffered. The -u option makes the output completely
unbuffered.
The -n option displays the output lines preceded by lines numbers, numbered sequentially from 1. Specifying the -b option with the -n
option omits the line numbers from blank lines.
The -s option crushes out multiple adjacent empty lines so that the output is displayed single spaced.
The -v option displays non-printing characters so that they are visible. Control characters print like ^X for control-x; the delete char-
acter (octal 0177) prints as ^?. Non-ascii characters (with the high bit set) are printed as M- (for meta) followed by the character of
the low 7 bits. A -e option may be given with the -v option, which displays a `$' character at the end of each line. Specifying the -t
option with the -v option displays tab characters as ^I.
SEE ALSO
cp(1), ex(1), more(1), pr(1), tail(1)
BUGS
Beware of `cat a b >a' and `cat a b >b', which destroy the input files before reading them.
4th Berkeley Distribution May 5, 1986 CAT(1)