Re: limiting performance impact of wal archiving.

[Kenneth Marshall <ktm@xxxxxxxx>]

On Tue, Nov 10, 2009 at 12:55:42PM +0100, Laurent Laborde wrote:
> Hi !
> We recently had a problem with wal archiving badly impacting the
> performance of our postgresql master.
> And i discovered "cstream", that can limite the bandwidth of pipe stream.
> 
> Here is our new archive command, FYI, that limit the IO bandwidth to 500KB/s  :
> archive_command = '/bin/cat %p | cstream -i "" -o "" -t -500k | nice
> gzip -9 -c | /usr/bin/ncftpput etc...'
> 
> 
> PS : While writing that mail, i just found that i could replace :
> cat %p | cstream -i "" ...
> with
> cstream -i %p ...
> *grins*
> 

And here is a simple perl program that I have used for a similar
reason. Obviously, it can be adapted to your specific needs.

Regards,
Ken

----throttle.pl-------
#!/usr/bin/perl -w

require 5.0;            # written for perl5, hasta labyebye perl4

use strict;
use Getopt::Std;

#
# This is an simple program to throttle network traffic to a
# specified  KB/second to allow a restore in the middle of the
# day over the network.
#

my($file, $chunksize, $len, $offset, $written, $rate, $buf );
my($options, $blocksize, $speed, %convert, $inv_rate, $verbose);

%convert = (              # conversion factors for $speed,$blocksize
	'',	'1',
	'w',	'2',
	'W',	'2',
	'b',	'512',
	'B',	'512',
	'k',	'1024',
	'K',	'1024',
);

$options = 'vhs:r:b:f:';

#
# set defaults
#
$speed = '100k';
$rate = '5';
$blocksize = '120k';              # Works for the DLT drives under SunOS
$file = '-';
$buf = '';
$verbose = 0;                     # default to quiet

sub usage {
  my($usage);

  $usage = "Usage: throttle [-s speed][-r rate/sec][-b blksize][-f file][-v][-h]
  (writes data to STDOUT)
  -s speed       max data rate in B/s - defaults to 100k 
  -r rate        writes/sec - defaults to 5
  -b size        read blocksize - defaults to 120k
  -f file        file to read for input - defaults to STDIN
  -h             print this message
  -v             print parameters used
";

  print STDERR $usage;
  exit(1);
}

getopts($options) || usage;

if ($::opt_h || $::opt_h) {
  usage;
}

usage unless $#ARGV < 0;

$speed = $::opt_s      if $::opt_s;
$rate = $::opt_r       if $::opt_r;
$blocksize = $::opt_b  if $::opt_b;
$file = $::opt_f       if $::opt_f;

#
# Convert $speed and $blocksize to bytes for use in the rest of the script
if ( $speed =~ /^(\d+)([wWbBkK]*)$/ ) {
  $speed = $1 * $convert{$2};
}
if ( $blocksize =~ /^(\d+)([wWbBkK]*)$/ ) {
  $blocksize = $1 * $convert{$2};
}
$inv_rate = 1/$rate;
$chunksize = int($speed/$rate);
$chunksize = 1 if $chunksize == 0;

if ($::opt_v || $::opt_v) {
  print STDERR "speed = $speed B/s\nrate = $rate/sec\nblocksize = $blocksize B\nchunksize = $chunksize B\n";
}

# Return error if unable to open file
open(FILE, "<$file") or die "Cannot open $file: $!\n";

# Read data from stdin and write it to stdout at a rate based
# on $rate and $speed.
#
while($len = sysread(FILE, $buf, $blocksize)) {
  #
  # print out in chunks of $speed/$rate size to allow a smoother load
  $offset = 0;
  while ($len) {
    $written = syswrite(STDOUT, $buf, $chunksize, $offset);
      die "System write error: $!\n" unless defined $written;
    $len -= $written;
    $offset += $written;
    #
    # Now wait 1/$rate seconds before doing the next block
    #
    select(undef, undef, undef, $inv_rate);
  }
}

close(FILE);

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