Ubuntu Manpage: paexec - parallel executor, distribute tasks over network or CPUs

NAME

       paexec - parallel executor, distribute tasks over network or CPUs

SYNOPSIS

       paexec [options]

       paexec -C [options] command [args...]

DESCRIPTION

       Suppose you have a long list of AUTONOMOUS tasks that need to be done, for example, you want to convert
       thousands of .wav audio files to .ogg format.  Also suppose that multiple CPUs are available, e.g. multi-
       CPU SMP system (or modern multikernel CPU) or a cluster consisting of individual computers connected to
       the network or internet. paexec can efficiently do this work, that is paexec efficiently distributes
       different tasks to different processors (or computers), receives the results of processing from them and
       sends these results to stdout.

       There are several notions that should be defined: task, command, transport, node.

       Tasks are read by paexec from stdin and are represented as one line of text, i.e. one input line - one
       task.

       node identifier - remote computer or CPU identifier, for example CPU ordinal number or computer's DNS
       name like node12.cluster.company.com.

       Command - user's program that reads one-line task from stdin and sends multiline result to stdout where
       an empty line means JOB_IS_DONE__I_AM_READY_FOR_THE_NEXT_ONE. After sending the empty line to stdout,
       stdout MUST BE FLUSHED. Remember that empty line MUST NOT appears in general result lines. Otherwise
       paexec may hang because of deadlock.

       Transport - special program that helps to run command on the node. It takes the node identifier as its
       first argument and command with its arguments as the rest.  For example, is '/usr/bin/ssh'. Both
       transport and command may be specified with their arguments, i.e. '/usr/bin/ssh -x' is allowed as a
       transport program.

       Algorithm. Commands are run on each node with a help of transport program. Then, tasks are read from
       stdin line-by-line (one task per line) and are sent to free node (exactly one task per node at a time).
       At the same time result lines are read from command's stdout and are output to paexec's stdout. When an
       empty line is obtained from the node (this means that node finished its job) it is marked as free and
       becomes ready for the next job. These steps repeat until the end of stdin is reached and all nodes finish
       their job.

       More formally (to better understand how paexec works):

          run_command_on_each_node
          mark_all_nodes_as_free
          while not(end_of_stdin) or not(all_nodes_are_free)
             while there_is_free_node/i and not(end_of_stdin)
                task = read_task_from_stdin
                send_task_to_node(task, i)
                mark_node_as_busy(i)
             end
             while result_line_from_node_is_available/i
                result = read_result_line_from_node(i)
                send_line_to_stdout(result)
                if is_empty_line(result)
                   # end of job
                   mark_node_as_free(i)
                end
             end
          end
          close_command_on_each_node

       Note that command that does your actual task is run once (per node), it is not restarted for every task.

       Also note that output contains result lines (obtained from different nodes) in the mixed order. That is,
       the first line of the output may contain a result line obtain from the first node, the second line of
       output - from the second node, but the third output line may contain result line from the first node
       again. It is also not guaranteed that the first line of output will be from the first node or from the
       first task. All result lines are output as soon as they are read by paexec, i.e as soon as they are ready
       to be output. paexec works this way for the efficiency reasons.  You can play with -l, -r and -p options
       to see what happens.

OPTIONS

-h Display help information.

-V Display version information.

-c command
Command with its arguments.

-C Command with its arguments are specified following the options.

-t transport
Transport command

-n +number
A number of commands to run in parallel.

-n nodes
List of nodes separated by space character. The first character must be alphanumeric, `_' or `/'.
All other characters are reserved for future extensions.

-n :filename
Filename containing list of nodes, one per line.

-x Run command specificed by -c for each task. Its stdout is passed to paexec. If both "-x" and "-g"
are specified, task is considered failed if command's exit status is non-zero.

-X Implies -x and ignore calculator's stdout.

-r Include node identifier or node number (0-based) to the output, i.e. id/number of node that
produces this particular output line. This identifier or number appears before line number if -l
is also applied. Space character is used as a separator.

-l Include a 0-based task number (input line number) to the output, i.e. line number from which this
particular output line was produced. It appears before pid if -p is also applied. Space character
is used as a separator.

-p Include pid of paexec's subprocess that communicates with node+command to the output. Pid prepends
the actual result line. Space character is used as a separator.

-e When end-of-task marker is obtained from node, an empty line is printed to stdout. This option may
be useful together with -l and/or -r.

-E Imply -e and flushes stdout.

-d Turn on a debugging mode (for debugging purposes only)

-i Copy input lines (i.e. tasks) to stdout.

-I Imply -i and flushes stdout.

-s|-g Orgraph of tasks (partially ordered set) is read from stdin.

Instead of autonomous tasks, graph of the tasks is read from stdin. In this mode every task can
either FAIL or SUCCEED. As always an empty line output by command means end of task. The line
before it shows an EXIT STATUS of the task. The word "failure" means failure, "success" - success
and "fatal" means that the current task is reassigned to another node (and restarted, of course)
(see option -z). See examples/1_div_x/cmd for the sample. An input line (paexec's stdin) should
contain either single task without spaces inside or two tasks separated by single space character,
e.g. task1<SPC>task2. task1<SPC>task2 line means that task1 must be done before task2 and it is
mandatory, that is if task1 fail all dependent tasks (including task2) are also failed recursively.
Tasks having dependencies are started only after all dependencies are succeeded. When a task
succeeds paexec outputs "success" word just before end_of_task marker (see -e or -E), otherwise
"failure" word is output followed by a list of tasks failed because of it.

Samples:

tasks (examples/make_package/tasks file)

textproc/dictem
devel/autoconf wip/libmaa
devel/gmake wip/libmaa
wip/libmaa wip/dict-server
wip/libmaa wip/dict-client
devel/m4 wip/dict-server
devel/byacc wip/dict-server
devel/byacc wip/dict-client
devel/flex wip/dict-server
devel/flex wip/dict-client
devel/glib2
devel/libjudy

command (examples/make_package/cmd__flex)

#!/usr/bin/awk -f
{
print $0
if ($0 == "devel/flex")
print "failure"
else
print "success"

print "" # end of task marker
fflush()
}

output of "paexec -s -l -c cmd__flex -n +10 \
< tasks"

3 devel/autoconf
3 success
4 devel/gmake
4 success
7 devel/m4
7 success
8 devel/byacc
8 success
9 devel/flex
9 failure
9 devel/flex wip/dict-server wip/dict-client
10 devel/glib2
10 success
11 devel/libjudy
11 success
1 textproc/dictem
1 success
2 wip/libmaa
2 success

-z If applied, read/write(2) operations from/to nodes becomes not critical. In case paexec has lost
connection to the node, it will reassign failed task to another node and, if -s applied, will
output "fatal" string to stdout ("success" + "failure" + "fatal"). This makes paexec resistant to
the I/O errors, as a result you can create paexec clusters even over network consisting of
unreliable hosts (Internet?). Failed hosts are marked as such and will not be used during the
current run of paexec.

-Z timeout
When -z applied, if a command fails, appropriate node is marked as broken and is excluded from the
following task distribution. But if -Z applied, every timeout seconds an attempt to rerun a comand
on a failed node is made. -Z implies -z. This option makes possible to organize clusters over
unreliable networks/hardware.

-w If -Z option were applied, paexec exits with error if ALL nodes failed. With -w it will not exit
and will wait for restoring nodes.

-m s=success
-m f=failure
-m F=fatal
-m t=eot
-m d=delimiter
Set alternative string for 'success', 'failure', 'fatal', '' (end of task) and ' ' (task delimiter
character). An empty string for 'fatal' means it will not be output to stdout in case of fatal
error.

-W num
When multiple machines or CPUs are used for tasks processing, it makes sense to start "heavier"
tasks as soon as possible in order to minimize total calculatiion time. If -W is specified,
special weight is assigned to each tasks which is used for reordering tasks. If num is 0, weights
themselves are used for reordering tasks. The bigger weight is, the more priority of the task is.
If num is 1, the total weight of task is a sum of its own weight (specified on input) and weights
of all tasks depending on it directly or indirectly. If num is 2, the total weight of task is a
maximum value of task's own weight and weights of all tasks depending on it directly or indirectly.
Weights are specified with a help of "weight:" keyword. If weight is not specified, it defaults to
1. The following is the example for input graph of tasks with weights.

weight: gtk2 30
weight: glib2 20
gtk2 firefox
weight: firefox 200
glib2 gtk2
weight: qt4 200
weight: kcachegrind 2
qt4 kcachegrind
qt4 djview4
tiff djview4
png djview4
weight: twm 1
weight: gqview 4

-y If applied, the magic string is used as an end-of-task marker instead of empty line. It is
unlikely that this line appears on calculator's output. This option has higher priority than
PAEXEC_EOT environment variable.

EXAMPLES

       1.
              paexec -t '/usr/bin/ssh -x' -n 'host1 host2 host3' \
                     -le -g -c calculate-me < tasks.txt |
              paexec_reorder -Mf -Sl

       2.
              ls -1 *.wav | paexec -x -n +4 -c 'oggenc -Q'

       3.
              ls -1 *.wav | paexec -xCil -n+4 flac -f --silent

       4.
              { uname -s; uname -r; uname -m; } |
              paexec -x -lp -n+2 -c banner |
              paexec_reorder -l

       For more examples see paexec.pdf and examples/ subdirectory in the distribution.

NOTES

       select(2) system call and non-blocking read(2) are used to read result lines from nodes.

       At the moment blocking write(2) is used to send task to the node. This may slow down an entire processing
       if tasks are too big. So, it is recommended to use shorter tasks, for example, filename or  URI  (several
       tens of bytes in size) instead of multi-megabyte content. Though this may be fixed in the future.

       Original  paexec  tarball  contains  a  number  of  sample  of use in presentation/paexec.pdf file. After
       installation you can find this file under share/doc/paexec/paexec.pdf or nearby.

ENVIRONMENT

       PAEXEC_BUFSIZE
             Overrides the compile time initial size for internal buffers used to store  tasks  and  the  result
             lines.  Versions  of  paexec prior to 0.9.0 used this value as a maximum buffer size.  Now internal
             buffers are resized automatically.  If unsure, do not set PAEXEC_BUFSIZE variable.  See the default
             value in Makefile.

       PAEXEC_ENV
             A list of variables passed to calculator.

       PAEXEC_EOT
             This variable sets the end-of-task marker which is an empty line by default.   Also,  through  this
             variable an end-of-task marker is passed to all calculators.

       PAEXEC_NODES
             Unless option -n was applied, this variables specifies the nodes.

       PAEXEC_TRANSPORT
             Unless option -t was applied, this variables specifies the transport.

BUGS/FEEDBACK

       Please  send  any comments, questions, bug reports etc. to me by e-mail or (even better) register them at
       sourceforge project home.  Feature requests are also welcomed.

HOME

       <http://sourceforge.net/projects/paexec>