# Ruby queue : rq-2.3.1 **URL:** \ **Category:** Ruby\ **Created:** [December 12, 2005, 12:18am UTC](https://www.ruby-forum.com/t/ruby-queue-rq-2-3-1/97195 "2005-12-12T00:18:08Z")\ **Posts on this page:** 1\ **Page:** 1
**Author:** ![casper\_the\_ghost](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/58956e/32.png) [@casper\_the\_ghost](https://www.ruby-forum.com/u/casper_the_ghost)\ **Post date:** [December 12, 2005, 12:18am UTC](https://www.ruby-forum.com/t/ruby-queue-rq-2-3-1/97195/1 "2005-12-12T00:18:08Z")
URIS: [http://codeforpeople.com/lib/ruby/rq/](http://codeforpeople.com/lib/ruby/rq/) [Linux Clustering with Ruby Queue: Small Is Beautiful | Linux Journal](http://www.linuxjournal.com/article/7922) [http://raa.ruby-lang.org/project/rq/](http://raa.ruby-lang.org/project/rq/) HISTORY: * * * 2.3.1: - added ‘stage’ option to submit mode, which allows submission in a ‘holding’ state. thanks to removed\_email\_address@domain.invalid for this fix! README: NAME rq v2.3.1 SYNOPSIS rq (queue | export RQ\_Q=q) mode [mode\_args]\* [options]\* DESCRIPTION ruby queue (rq) is a tool used to create instant linux clusters by managing sqlite databases as nfs mounted priority work queues. multiple instances of rq running from multiples hosts can work from these queues to distribute processing load to n nodes - bringing many dozens of otherwise powerful cpus to their knees with a single blow. clearly this software should be kept out of the hands of free radicals, seti enthusiasts, and mr. jeff safran. ``` the central concept of rq is that n nodes work in isolation to pull ``` jobs from an central nfs mounted priority work queue in a synchronized fashion. the nodes have absolutely no knowledge of each other and all communication if done via the queue meaning that, so long as the queue is available via nfs and a single node is running jobs from it, the system will continue to process jobs. there is no centralized process whatsoever - all nodes work to take jobs from the queue and run them as fast as possible. this creates a system which load balances automatically and is robust in face of node failures. ``` the first argument to any rq command is the name of the queue. ``` this name may be omitted if, and only if, the environment variable RQ\_Q has been set to contain the absolute path of target queue. ``` rq operates in one of the modes create, submit, resubmit, list, ``` status, delete, update, query, execute, configure, snapshot, lock, backup, rotate, feed, or help. depending on the mode of operation and the options used the meaning of ‘mode\_args’ may change. MODES ``` the following mode abbreviations exist c => create s => submit r => resubmit l => list ls => list t => status d => delete rm => delete u => update q => query e => execute C => configure S => snapshot L => lock b => backup R => rotate f => feed h => help not all modes have abbreviations create, c : create a queue. the queue must be located on an nfs mounted file ``` system visible from all nodes intended to run jobs from it. nfs locking must be functional on this file system. ``` examples : 0) to create a queue ~ > rq /path/to/nfs/mounted/q create or simply ~ > rq /path/to/nfs/mounted/q c submit, s : submit jobs to a queue to be proccesed by a feeding node. any ``` ‘mode\_args’ are taken as the command to run. note that ‘mode\_args’ are subject to shell expansion - if you don’t understand what this means do not use this feature and pass jobs on stdin. ``` when running in submit mode a file may by specified as a list of ``` commands to run using the ‘–infile, -i’ option. this file is taken to be a newline separated list of commands to submit, blank lines and comments (#) are allowed. if submitting a large number of jobs the input file method is MUCH, more efficient. if no commands are specified on the command line rq automatically reads them from STDIN. yaml formatted files are also allowed as input ([http://www.yaml.org/](http://www.yaml.org/)) - note that the output of nearly all rq commands is valid yaml and may, therefore, be piped as input into the submit command. the leading ‘—’ of yaml file may not be omitted. ``` when submitting the '--priority, -p' option can be used here to ``` determine the priority of jobs. priorities may be any whole number - zero is the default. note that submission of a high priority job will NOT supplant currently running low priority jobs, but higher priority jobs WILL always migrate above lower priority jobs in the queue in order that they be run as soon as possible. constant submission of high priority jobs may create a starvation situation whereby low priority jobs are never allowed to run. avoiding this situation is the responsibility of the user. the only guaruntee rq makes regarding job execution is that jobs are executed in an ‘oldest highest priority’ order and that running jobs are never supplanted. jobs submitted with the ‘–stage’ option will not be run by any node and will remain in a ‘holding’ state until updated (see update mode) into the ‘pending’ mode, this option allows jobs to entered, or staged, in the queue and made candidates for running at a later date. ``` examples : 0) submit the job ls to run on some feeding host ~ > rq q s ls 1) submit the job ls to run on some feeding host, at priority 9 ~ > rq -p9 q s ls 2) submit 42000 jobs (quietly) from a command file, marking ``` them as restartable should the node they are running on reboot. ``` ~ > wc -l cmdfile 42000 ~ > rq q s --quiet --restartable < cmdfile 3) submit 42 priority 9 jobs from a command file. ~ > wc -l cmdfile 42 ~ > rq -p9 q s < cmdfile 4) submit 42 priority 9 jobs from a command file, marking them ``` as ‘important’ using the ‘–tag, -t’ option. ``` ~ > wc -l cmdfile 42 ~ > rq -p9 -timportant q s < cmdfile 5) re-submit all the 'important' jobs (see 'query' section ``` below) ``` ~ > rq q query tag=important | rq q s 6) re-submit all jobs which are already finished (see 'list' ``` section below) ``` ~ > rq q l f | rq q s 7) stage the job wont_run_yet to the queue in a 'holding' ``` state. no feeder will run this job until it’s state is upgraded to ‘pending’ ``` ~ > rq q s --stage wont_run_yet resubmit, r : resubmit jobs back to a queue to be proccesed by a feeding node. ``` resubmit is essentially equivalent to submitting a job that is already in the queue as a new job and then deleting the original job except that using resubmit is atomic and, therefore, safer and more efficient. read docs for delete and submit for more info. ``` examples : 0) resubmit job 42 to the queue. afterwards list, l, ls : list mode lists jobs of a certain state or job id. state may be ``` one of pending, holding, running, finished, dead, or all. any ‘mode\_args’ that are numbers are taken to be job id’s to list. ``` states may be abbreviated to uniqueness, therefore the following ``` shortcuts apply : ``` p => pending h => holding r => running f => finished d => dead a => all examples : 0) show everything in q ~ > rq q list all or ~ > rq q l all or ~ > export RQ_Q=q ~ > rq l 1) show q's pending jobs ~ > rq q list pending 2) show q's running jobs ~ > rq q list running 3) show q's finished jobs ~ > rq q list finished 4) show job id 42 ~ > rq q l 42 5) show q's holding jobs ~ > rq q list holding status, t : status mode shows the global state the queue. there are no ``` ‘mode\_args’. the meaning of each state is as follows: ``` pending => no feeder has yet taken this job holding => a hold has been placed on this job, thus no feeder ``` will start it running =\> a feeder has taken this job finished =\> a feeder has finished this job dead =\> rq died while running a job, has restarted, and moved this job to the dead state ``` note that rq cannot move jobs into the dead state unless it has ``` been restarted. this is because no node has any knowledge of other nodes and cannot possibly know if a job was started on a node that died, or is simply taking a very long time. only the node that dies, upon restart, can determine that is has jobs that ‘were started before it started’ and move these jobs into the dead state. normally only a machine crash would cause a job to be placed into the dead state. dead jobs are never automatically restarted, this is the responsibility of an operator. ``` examples : 0) show q's status ~ > rq q t delete, d : delete combinations of pending, holding, finished, dead, or jobs ``` specified by jid. the delete mode is capable of parsing the output of list and query modes, making it possible to create custom filters to delete jobs meeting very specific conditions. ``` 'mode_args' are the same as for list. note that it is NOT possible to delete a running job. rq has a decentralized architechture which means that compute nodes are ``` completely independant of one another; an extension is that there is no way to communicate the deletion of a running job from the queue the the node actually running that job. it is not an error to force a job to die prematurely using a facility such as an ssh command spawned on the remote host to kill it. once a job has been noted to have finished, whatever the exit status, it can be deleted from the queue. ``` examples : 0) delete all pending, finished, and dead jobs from a queue ~ > rq q d all 1) delete all pending jobs from a queue ~ > rq q d p 2) delete all finished jobs from a queue ~ > rq q d f 3) delete jobs via hand crafted filter program ~ > rq q list | yaml_filter_prog | rq q d an example ruby filter program (you have to love this) require 'yaml' joblist = YAML::load STDIN y joblist.select{|job| job['command'] =~ /bombing_program/} this program reads the list of jobs (yaml) from stdin and ``` then dumps only those jobs whose command matches ‘bombing\_program’, which is subsequently piped to the delete command. ``` update, u : update assumes all leading arguments are jids to update with ``` subsequent key=value pairs. currently only the ‘command’, ‘priority’, and ‘tag’ fields of pending jobs can be generically updated and the ‘state’ field may be toggled between pending and holding. ``` examples: 0) update the priority of job 42 ~ > rq q update 42 priority=7 1) update the priority of all pending jobs ~ > rq q update pending priority=7 2) query jobs with a command matching 'foobar' and update their ``` command to be ‘barfoo’ ``` ~ > rq q q "command like '%foobar%'" |\ rq q u command=barfoo 3) place a hold on jid 2 ~ > rq q u 2 state=holding 4) place a hold on all jobs with tag=disk_filler ~ > rq q q tag=disk_filler | rq q u state=holding 5) remove the hold on jid 2 ~ > rq q u 2 state=pending query, q : query exposes the database more directly the user, evaluating the ``` where clause specified on the command line (or read from STDIN). this feature can be used to make a fine grained slection of jobs for reporting or as input into the delete command. you must have a basic understanding of SQL syntax to use this feature, but it is fairly intuitive in this limited capacity. ``` examples: 0) show all jobs submitted within a specific 10 minute range ~ > rq q query "started >= '2004-06-29 22:51:00' and started ``` \< ‘2004-06-29 22:51:10’" ``` 1) shell quoting can be tricky here so input on STDIN is also ``` allowed to avoid shell expansion ``` ~ > cat constraints.txt started >= '2004-06-29 22:51:00' and started < '2004-06-29 22:51:10' ~ > rq q query < contraints.txt or (same thing) ~ > cat contraints.txt| rq q query 2) this query output might then be used to delete those jobs ~ > cat contraints.txt | rq q q | rq q d 3) show all jobs which are either finished or dead ~ > rq q q "state='finished' or state='dead'" 4) show all jobs which have non-zero exit status ~ > rq q query exit_status!=0 5) if you plan to query groups of jobs with some common feature ``` consider using the ‘–tag, -t’ feature of the submit mode which allows a user to tag a job with a user defined string which can then be used to easily query that job group ``` ~ > rq q submit --tag=my_jobs < joblist ~ > rq q query tag=my_jobs 6) in general all but numbers will need to be surrounded by ``` single quotes unless the query is a ‘simple’ one. a simple query is a query with no boolean operators, not quotes, and where every part of it looks like ``` key op value with **NO SPACES** between key, op, and value. if, and ``` only if, the query is ‘simple’ rq will contruct the where clause appropriately. the operators accepted, and their meanings, are ``` = : equivalence : sql = =~ : matches : sql like !~ : not matches : sql not like match, in the context is **NOT** a regular expression but ``` a sql style string match. about all you need to know about sql matches is that the ‘%’ char matches anything. multiple simple queries will be joined with boolean ‘and’ ``` this sounds confusing - it isn't. here are some examples of ``` simple queries ``` 6.a) query : rq q query tag=important where_clause : "( tag = 'important' )" 6.b) query : rq q q priority=6 restartable=true where_clause : "( priority = 6 ) and ( restartable = 'true' )" 6.c) query : rq q q command=~%bombing_job% runner=~%node_1% where_clause : "( command like '%bombing_job%') and (runner like ``` ‘%node\_1%’)" ``` execute, e : execute mode is to be used by expert users with a knowledge of ``` sql syntax only. it follows the locking protocol used by rq and then allows the user to execute arbitrary sql on the queue. unlike query mode a write lock on the queue is obtained allowing a user to definitively shoot themselves in the foot. for details on a queue’s schema the file ‘db.schema’ in the queue directory should be examined. ``` examples : 0) list all jobs ~ > rq q execute 'select * from jobs' configure, C : this mode is not supported yet. snapshot, p : snapshot provides a means of taking a snapshot of the q. use this ``` feature when many queries are going to be run; for example when attempting to figure out a complex pipeline command your test queries will not compete with the feeders for the queue’s lock. you should use this option whenever possible to avoid lock competition. ``` examples: 0) take a snapshot using default snapshot naming, which is made ``` via the basename of the q plus ‘.snapshot’ ``` ~ > rq /path/to/nfs/q snapshot 1) use this snapshot to chceck status ~ > rq ./q.snapshot status 2) use the snapshot to see what's running on which host ~ > rq ./q.snapshot list running | grep `hostname` note that there is also a snapshot option - this option is not ``` the same as the snapshot command. the option can be applied to ANY command. if in effect then that command will be run on a snapshot of the database and the snapshot then immediately deleted. this is really only useful if one were to need to run a command against a very heavily loaded queue and did not wish to wait to obtain the lock. eg. ``` 0) get the status of a heavily loaded queue ~ > rq q t --snapshot 1) same as above ~ > rq q t -s **IMPORTANT** a really great way to hang all processing in your queue is to ``` do this ``` rq q list | less and then leave for the night. you hold a read lock you won't ``` release until less dies. this is what snapshot is made for! use it like ``` rq q list -s | less now you've taken a snapshot of the queue to list so your locks ``` affect no one. ``` lock, L : lock the queue and then execute an arbitrary shell command. lock ``` mode uses the queue’s locking protocol to safely obtain a lock of the specified type and execute a command on the user’s behalf. lock type must be one of ``` (r)ead | (sh)ared | (w)rite | (ex)clusive examples : 0) get a read lock on the queue and make a backup ~ > rq q L read -- cp -r q q.bak (the '--' is needed to tell rq to stop parsing command line options which allows the '-r' to be passed to the 'cp' ``` command) ``` **IMPORTANT** this is another fantastic way to freeze your queue - use with ``` care! ``` backup, b : backup mode is exactly the same as getting a read lock on the ``` queue and making a copy of it. this mode is provided as a convenience. ``` 0) make a backup of the queue using default naming ( qname + ``` timestamp + .bak ) ``` ~ > rq q b 1) make a backup of the queue as 'q.bak' ~ > rq q b q.bak rotate, r : rotate mode is conceptually similar to log rolling. normally the ``` list of finished jobs will grow without bound in a queue unless they are manually deleted. rotation is a method of trimming finished jobs from a queue without deleting them. the method used is that the queue is copied to a ‘rotation’; all jobs that are dead or finished are deleted from the original queue and all pending and running jobs are deleted from the rotation. in this way the rotation becomes a record of the queue’s finished and dead jobs at the time the rotation was made. ``` 0) rotate a queue using default rotation name ~ > rq q rotate 1) rotate a queue naming the rotation ~ > rq q rotate q.rotation 2) a crontab entry like this could be used to rotate a queue ``` daily ``` 59 23 * * * rq q rotate `date +q.%Y%m%d` feed, f : take jobs from the queue and run them on behalf of the submitter ``` as quickly as possible. jobs are taken from the queue in an ‘oldest highest priority’ first order. ``` feeders can be run from any number of nodes allowing you to ``` harness the CPU power of many nodes simoultaneously in order to more effectively clobber your network, anoy your sysads, and set output raids on fire. ``` the most useful method of feeding from a queue is to do so in ``` daemon mode so that if the process loses it’s controling terminal it will not exit when you exit your terminal session. use the ‘–daemon, -d’ option to accomplish this. by default only one feeding process per host per queue is allowed to run at any given moment. because of this it is acceptable to start a feeder at some regular interval from a cron entry since, if a feeder is alreay running, the process will simply exit and otherwise a new feeder will be started. in this way you may keep feeder processing running even acroess machine reboots without requiring sysad intervention to add an entry to the machine’s startup tasks. ``` examples : 0) feed from a queue verbosely for debugging purposes, using a ``` minimum and maximum polling time of 2 and 4 respectively. you would NEVER specify polling times this brief except for debugging purposes!!! ``` ~ > rq q feed -v4 -m2 -M4 1) same as above, but viewing the executed sql as it is sent to ``` the database ``` ~ > RQ_SQL_DEBUG=1 rq q f -v4 -m2 -M4 2) feed from a queue in daemon mode - logging to ``` /home/ahoward/rq.log ``` ~ > rq q f -d -l/home/ahoward/rq.log log rolling in daemon mode is automatic so your logs should ``` never need to be deleted to prevent disk overflow. ``` 3) use something like this sample crontab entry to keep a ``` feeder running forever - it attempts to (re)start every fifteen minutes but exits if another process is already feeding. ``` # # your crontab file - sample only # */15 * * * * /full/path/to/bin/rq /full/path/to/nfs/mounted/q ``` f -d -l/home/username/cfq.log -q ``` the '--quiet, -q' here tells rq to exit quietly (no STDERR) when another process is found to already be feeding so that ``` no cron message would be sent under these conditions. ``` start : the start mode is equivalent to running the feed mode except the ``` –daemon is implied so the process instantly goes into the background. also, if no log (–log) is specified in start mode a default one is used. the default is ``` ENV['HOME'] + '/' + File::basename(queue) + '.log' the crontab line above could just as well be */15 * * * * /full/path/to/bin/rq /full/path/to/nfs/mounted/q ``` start -q ``` with the resulting log ending up in ~/q.log examples : 0) start a daemon process feeding from q ~ > rq q start shutdown : tell a running feeder to finish any pending jobs and then to ``` exit. this is equivalent to sending signal ‘SIGTERM’ to the process - this is what using ‘kill pid’ does by default. ``` examples : 0) stop a feeding process, if any, that is feeding from q. ``` allow all jobs to be finished first. ``` ~ > rq q shutdown **VERY IMPORTANT** if you are keeping your feeder alive with a crontab entry ``` you’ll need to comment it out before doing this or else it will simply re-start!!! ``` stop : tell any running feeder to stop NOW. this sends signal 'SIGKILL' ``` (-9) to the feeder process. the same warning as for shutdown applies!!! ``` examples : 0) stop a feeding process, if any, that is feeding from q. ``` allow NO jobs to be finished first - exit instantly. ``` ~ > rq q stop feeder : show the pid, if any, of the feeder ~ > rq q feeder feeder <15366> help, h : this message examples : 0) get this message ~> rq q help or ~> rq help ``` NOTES - realize that your job is going to be running on a remote host and this has implications. paths, for example, should be absolute, not relative. specifically the submitted job script must be visible from all hosts currently feeding from a queue as must be the input and output files/directories. ``` - jobs are currently run under the bash shell using the --login ``` option. therefore any settings in your .bashrc will apply - specifically your PATH setting. you should not, however, rely on jobs running with any given environment. ``` - you need to consider __CAREFULLY__ what the ramifications of ``` having multiple instances of your program all potentially running at the same time will be. for instance, it is beyond the scope of rq to ensure multiple instances of a given program will not overwrite each others output files. coordination of programs is left entirely to the user. ``` - the list of finished jobs will grow without bound unless you ``` sometimes delete some (all) of them. the reason for this is that rq cannot know when the user has collected the exit\_status of a given job, and so keeps this information in the queue forever until instructed to delete it. if you have collected the exit\_status of you job(s) it is not an error to then delete that job from the finished list - the information is kept for your informational purposes only. in a production system it would be normal to periodically save, and then delete, all finished jobs. ``` - know that it is a VERY bad idea to spawn several dozen process ``` all reading/writing huge output files to a single NFS server. use this paradigm instead ``` copy data locally from input space work on date move data to output space the vsftp daemon is an excellent utility to have running on hosts ``` in your cluster so anonymous ftp can be used to get/put data. ``` - know that nfs locking is very, very easy to break with firewalls ``` put in place by over zealous system administrators. be postive not only that nfs locking works, but that lock recovery server/client crash or reboot works as well. [http://nfs.sourceforge.net/](http://nfs.sourceforge.net/) is the place to learn about NFS. my experience thus far is that there are ZERO properly configured NFS installations in the world. please test yours. contact me for a simple script which can assist you. donations of beer may be required. ENVIRONMENT RQ\_Q: set to the full path of nfs mounted queue ``` the queue argument to all commands may be omitted if, and only ``` if, the environment variable ‘RQ\_Q’ contains the full path to the q. eg. ``` ~ > export RQ_Q=/full/path/to/my/q this feature can save a considerable amount of typing for those ``` weak of wrist. DIAGNOSTICS success : $? == 0 failure : $? != 0 CREDITS - kim baugh : patient tester and design input - jeff safran : the guy can break anything - chris elvidge : made it possible - trond myklebust : tons of help with nfs - jamis buck : for writing the sqlite bindings for ruby - \_why : for writing yaml for ruby - matz : for writing ruby AUTHOR removed\_email\_address@domain.invalid BUGS 0 \< bugno && bugno \<= 42 ``` reports to removed_email_address@domain.invalid ``` OPTIONS –priority=priority, -p modes : set the job(s) priority - lowest(0) … highest(n) - (default 0) –tag=tag, -t modes : set the job(s) user data tag –runner=runner modes : set the job(s) required runner(s) –restartable modes : set the job(s) to be restartable on node reboot –stage modes : set the job(s) initial state to be holding (default pending) –infile=infile modes : infile –quiet, -q modes \ : do not echo submitted jobs, fail silently if another process is already feeding –daemon, -D modes : spawn a daemon –max\_feed=max\_feed modes : the maximum number of concurrent jobs run –retries=retries modes : specify transaction retries –min\_sleep=min\_sleep modes : specify min sleep –max\_sleep=max\_sleep modes : specify max sleep –snapshot, -s operate on snapshot of queue –verbosity=verbostiy, -v 0|fatal \< 1|error \< 2|warn \< 3|info \< 4|debug - (default info) –log=path, -l set log file - (default stderr) –log\_age=log\_age daily | weekly | monthly - what age will cause log rolling (default nil) –log\_size=log\_size size in bytes - what size will cause log rolling (default nil) –help, -h this message –version show version number enjoy. -a