bugGNU Parallel - build and execute command lines from standard input in parallel - Bugs: bug #36456, spawn sshs slower to avoid htting...

 
 

bug #36456: spawn sshs slower to avoid htting MaxStartup

Submitted by:  Ole Tange <tange>
Submitted on:  Sat 12 May 2012 11:38:00 PM UTC  
 
Category: NoneSeverity: 3 - Normal
Item Group: NoneStatus: Fixed
Privacy: PublicAssigned to: Ole Tange <tange>
Open/Closed: Closed

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Tue 02 Jul 2013 07:48:24 PM UTC, comment #4:

Probably fixed in 20130630 alpha.

Ole Tange <tange>
Project AdministratorIn charge of this item.
Mon 06 Aug 2012 11:04:04 PM UTC, comment #3:

Using --joblog we can run ssh to all hosts in parallel twice and get the timings with ms accuracity.

It requires --plain to work as we need to be able to ignore all --profile/$PARALLEL etc.

Ole Tange <tange>
Project AdministratorIn charge of this item.
Mon 06 Aug 2012 11:03:56 PM UTC, comment #2:

Auto master connection does not solve this.

https://lists.gnu.org/archive/html/parallel/2012-08/msg00012.html

Ole Tange <tange>
Project AdministratorIn charge of this item.
Tue 22 May 2012 11:30:29 PM UTC, comment #1:

We also need to see if this can be fixed using auto master connection

Ole Tange <tange>
Project AdministratorIn charge of this item.
Sat 12 May 2012 11:38:00 PM UTC, original submission:

sshd has MaxStartup which limits how many ssh connections that can be in login state (typically 10).

To avoid hitting that limit GNU Parallel should wait a little between spawning another ssh to the same host. The time to wait could be the time it takes to run:

ssh remote echo foo

as that will be a full login. It should be run twice and the first be ignored, as DNS may account for the most of the delay.

Maybe a better wait time is the above time / 10 (for MaxStartup) * 2 (for 100% error margin).

To time this use:

use Time::HiRes qw ( time );

time() without hires will give time in seconds and if added 1 second it will give a pessimistic time.

Experiments:

time ssh m echo foo
0.086s
sleep 0.004;ssh m echo & # This works

time ssh l echo foo
5.1s
sleep 0.1;ssh l echo & # This works

time ssh n echo
0.198s
sleep 0.02;ssh n echo & # This works

time ssh n2 echo
0.211s
sleep 0.03;ssh n2 echo & # This works

Ole Tange <tange>
Project AdministratorIn charge of this item.

 

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    Follow 3 latest changes.

    Date Changed By Updated Field Previous Value => Replaced By
    Tue 02 Jul 2013 07:48:24 PM UTCtangeStatusNone=>Fixed
      Open/ClosedOpen=>Closed
    Mon 06 Aug 2012 11:03:56 PM UTCtangeAssigned toNone=>tange

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