Gearman Protocol

This file is maintained in the gearmand project on Github, so any modifications should be made there.

Gearman Protocol
----------------

The Gearman protocol operates over TCP, port 4730 by default. It
previously operated on port 7003, but this conflicted with the AFS
port range and the new port (4730) was assigned by IANA. Communication
happens between either a client and job server, or between a worker
and job server. In either case, the protocol consists of packets
containing requests and responses. All packets sent to a job server
are considered requests, and all packets sent from a job server are
considered responses. A simple configuration may look like:

---------- ---------- ---------- ----------
| Client | | Client | | Client | | Client |
---------- ---------- ---------- ----------
\ / \ /
\ / \ /
-------------- --------------
| Job Server | | Job Server |
-------------- --------------
| |
----------------------------------------------
| | | |
---------- ---------- ---------- ----------
| Worker | | Worker | | Worker | | Worker |
---------- ---------- ---------- ----------

Initially, the workers register functions they can perform with each
job server. Clients will then connect to a job server and issue a
request to a job to be run. The job server then notifies each worker
that can perform that job (based on the function it registered) that
a new job is ready. The first worker to wake up and retrieve the job
will then execute it.

All communication between workers or clients and the job server
are binary. There is also a line-based text protocol used by
administrative clients. This part of the protocol is text based so a
custom administrative utility is not required (instead, 'telnet' or
'nc' can be used). This is documented under "Administrative Protocol".


Binary Packet
-------------

Requests and responses are encapsulated by a binary packet. A binary
packet consists of a header which is optionally followed by data. The
header is:

4 byte magic code - This is either "\0REQ" for requests or "\0RES"
for responses.

4 byte type - A big-endian (network-order) integer containing
an enumerated packet type. Possible values are:

# Name Magic Type
1 CAN_DO REQ Worker
2 CANT_DO REQ Worker
3 RESET_ABILITIES REQ Worker
4 PRE_SLEEP REQ Worker
5 (unused) - -
6 NOOP RES Worker
7 SUBMIT_JOB REQ Client
8 JOB_CREATED RES Client
9 GRAB_JOB REQ Worker
10 NO_JOB RES Worker
11 JOB_ASSIGN RES Worker
12 WORK_STATUS REQ Worker
RES Client
13 WORK_COMPLETE REQ Worker
RES Client
14 WORK_FAIL REQ Worker
RES Client
15 GET_STATUS REQ Client
16 ECHO_REQ REQ Client/Worker
17 ECHO_RES RES Client/Worker
18 SUBMIT_JOB_BG REQ Client
19 ERROR RES Client/Worker
20 STATUS_RES RES Client
21 SUBMIT_JOB_HIGH REQ Client
22 SET_CLIENT_ID REQ Worker
23 CAN_DO_TIMEOUT REQ Worker
24 ALL_YOURS REQ Worker
25 WORK_EXCEPTION REQ Worker
RES Client
26 OPTION_REQ REQ Client/Worker
27 OPTION_RES RES Client/Worker
28 WORK_DATA REQ Worker
RES Client
29 WORK_WARNING REQ Worker
RES Client
30 GRAB_JOB_UNIQ REQ Worker
31 JOB_ASSIGN_UNIQ RES Worker
32 SUBMIT_JOB_HIGH_BG REQ Client
33 SUBMIT_JOB_LOW REQ Client
34 SUBMIT_JOB_LOW_BG REQ Client
35 SUBMIT_JOB_SCHED REQ Client
36 SUBMIT_JOB_EPOCH REQ Client
37 SUBMIT_REDUCE_JOB REQ Client
38 SUBMIT_REDUCE_JOB_BACKGROUND REQ Client
39 GRAB_JOB_ALL REQ Worker
40 JOB_ASSIGN_ALL RES Worker
41 GET_STATUS_UNIQUE REQ Client
42 STATUS_RES_UNIQUE RES Client


4 byte size - A big-endian (network-order) integer containing
the size of the data being sent after the header.

Arguments given in the data part are separated by a NULL byte, and
the last argument is determined by the size of data after the last
NULL byte separator. All job handle arguments must not be longer than
64 bytes, including NULL terminator.


Client/Worker Requests
----------------------

These request types may be sent by either a client or a worker:

ECHO_REQ

When a job server receives this request, it simply generates a
ECHO_RES packet with the data. This is primarily used for testing
or debugging.

Arguments:
- Opaque data that is echoed back in response.


Client/Worker Responses
-----------------------

These response types may be sent to either a client or a worker:

ECHO_RES

This is sent in response to a ECHO_REQ request. The server doesn't
look at or modify the data argument, it just sends it back.

Arguments:
- Opaque data that is echoed back in response.

ERROR

This is sent whenever the server encounters an error and needs
to notify a client or worker.

Arguments:
- NULL byte terminated error code string.
- Error text.


Client Requests
---------------

These request types may only be sent by a client:

SUBMIT_JOB, SUBMIT_JOB_BG,
SUBMIT_JOB_HIGH, SUBMIT_JOB_HIGH_BG,
SUBMIT_JOB_LOW, SUBMIT_JOB_LOW_BG

A client issues one of these when a job needs to be run. The
server will then assign a job handle and respond with a JOB_CREATED
packet.

If on of the BG versions is used, the client is not updated with
status or notified when the job has completed (it is detached).

The Gearman job server queue is implemented with three levels:
normal, high, and low. Jobs submitted with one of the HIGH versions
always take precedence, and jobs submitted with the normal versions
take precedence over the LOW versions.

The unique ID can be used by the server to reduce queue length. If a
job with the same Unique ID has already been submitted, the server
may attach this request to the already existing job. This includes
jobs already in progress, in which case non-background jobs will be
sent the same result as background jobs. This is known commonly as
"coalescing".

Arguments:
- NULL byte terminated function name.
- NULL byte terminated unique ID.
- Opaque data that is given to the function as an argument.

SUBMIT_REDUCE_JOB, SUBMIT_REDUCE_JOB_BACKGROUND

Works like the other SUBMIT_JOB commands, but adds a reducer argument.

Arguments:
- NULL byte terminated function name.
- NULL byte terminated unique ID.
- NULL byte terminated reducer.
- Opaque data that is given to the function as an argument.

SUBMIT_JOB_SCHED

Just like SUBMIT_JOB_BG, but run job at given time instead of
immediately. This is not currently used and may be removed.

Arguments:
- NULL byte terminated function name.
- NULL byte terminated unique ID.
- NULL byte terminated minute (0-59).
- NULL byte terminated hour (0-23).
- NULL byte terminated day of month (1-31).
- NULL byte terminated month (1-12).
- NULL byte terminated day of week (0-6, 0 = Monday).
- Opaque data that is given to the function as an argument.

SUBMIT_JOB_EPOCH

Just like SUBMIT_JOB_BG, but run job at given time instead of
immediately. This is not currently used and may be removed.

Arguments:
- NULL byte terminated function name.
- NULL byte terminated unique ID.
- NULL byte terminated epoch time.
- Opaque data that is given to the function as an argument.

GET_STATUS

A client issues this to get status information for a submitted job.

Arguments:
- Job handle that was given in JOB_CREATED packet.

GET_STATUS_UNIQUE

A client issues this to get status information for a submitted job.

Arguments:
- Unique value that was given when job was submitted.

OPTION_REQ

A client issues this to set an option for the connection in the
job server. Returns a OPTION_RES packet on success, or an ERROR
packet on failure.

Arguments:
- Name of the option to set. Possibilities are:
* "exceptions" - Forward WORK_EXCEPTION packets to the client.


Client Responses
----------------

These response types may only be sent to a client:

JOB_CREATED

This is sent in response to one of the SUBMIT_JOB* packets. It
signifies to the client that a the server successfully received
the job and queued it to be run by a worker.

Arguments:
- Job handle assigned by server.

WORK_DATA, WORK_WARNING, WORK_STATUS, WORK_COMPLETE,
WORK_FAIL, WORK_EXCEPTION

For non-background jobs, the server forwards these packets from
the worker to clients. See "Worker Requests" for more information
and arguments.

STATUS_RES

This is sent in response to a GET_STATUS request. This is used by
clients that have submitted a job with SUBMIT_JOB_BG to see if the
job has been completed, and if not, to get the percentage complete.

Arguments:
- NULL byte terminated job handle.
- NULL byte terminated known status, this is 0 (false) or 1 (true).
- NULL byte terminated running status, this is 0 (false) or 1
(true).
- NULL byte terminated percent complete numerator.
- Percent complete denominator.

STATUS_RES_UNIQUE

This is sent in response to a GET_STATUS_UNIQUE request. This is
used by clients that have submitted a job with SUBMIT_JOB_BG to see
if the job has been completed, and if not, to get the percentage
complete.

Arguments:
- NULL byte terminated job handle.
- NULL byte terminated known status, this is 0 (false) or 1 (true).
- NULL byte terminated running status, this is 0 (false) or 1
(true).
- NULL byte terminated percent complete numerator.
- NULL byte terminated percent complete denominator.
- Count of clients waiting.

OPTION_RES

Successful response to the OPTION_REQ request.

Arguments:
- Name of the option that was set, see OPTION_REQ for possibilities.


Worker Requests
---------------

These request types may only be sent by a worker:

CAN_DO

This is sent to notify the server that the worker is able to
perform the given function. The worker is then put on a list to be
woken up whenever the job server receives a job for that function.

Arguments:
- Function name.

CAN_DO_TIMEOUT

Same as CAN_DO, but with a timeout value on how long the job
is allowed to run. After the timeout value, the job server will
mark the job as failed and notify any listening clients.

Arguments:
- NULL byte terminated Function name.
- Timeout value.

CANT_DO

This is sent to notify the server that the worker is no longer
able to perform the given function.

Arguments:
- Function name.

RESET_ABILITIES

This is sent to notify the server that the worker is no longer
able to do any functions it previously registered with CAN_DO or
CAN_DO_TIMEOUT.

Arguments:
- None.

PRE_SLEEP

This is sent to notify the server that the worker is about to
sleep, and that it should be woken up with a NOOP packet if a
job comes in for a function the worker is able to perform.

Arguments:
- None.

GRAB_JOB

This is sent to the server to request any available jobs on the
queue. The server will respond with either NO_JOB or JOB_ASSIGN,
depending on whether a job is available.

Arguments:
- None.

GRAB_JOB_UNIQ

Just like GRAB_JOB, but return JOB_ASSIGN_UNIQ when there is a job.

Arguments:
- None.

GRAB_JOB_ALL

Just like GRAB_JOB_UNIQ, but return JOB_ASSIGN_ALL when there is a job.

Arguments:
- None.

WORK_DATA

This is sent to update the client with data from a running job. A
worker should use this when it needs to send updates, send partial
results, or flush data during long running jobs. It can also be
used to break up a result so the worker does not need to buffer
the entire result before sending in a WORK_COMPLETE packet.

Arguments:
- NULL byte terminated job handle.
- Opaque data that is returned to the client.

WORK_WARNING

This is sent to update the client with a warning. It acts just
like a WORK_DATA response, but should be treated as a warning
instead of normal response data.

Arguments:
- NULL byte terminated job handle.
- Opaque data that is returned to the client.

WORK_STATUS

This is sent to update the server (and any listening clients)
of the status of a running job. The worker should send these
periodically for long running jobs to update the percentage
complete. The job server should store this information so a client
who issued a background command may retrieve it later with a
GET_STATUS request.

Arguments:
- NULL byte terminated job handle.
- NULL byte terminated percent complete numerator.
- Percent complete denominator.

WORK_COMPLETE

This is to notify the server (and any listening clients) that
the job completed successfully.

Arguments:
- NULL byte terminated job handle.
- Opaque data that is returned to the client as a response.

WORK_FAIL

This is to notify the server (and any listening clients) that
the job failed.

Arguments:
- Job handle.

WORK_EXCEPTION

This is to notify the server (and any listening clients) that
the job failed with the given exception.

Arguments:
- NULL byte terminated job handle.
- Opaque data that is returned to the client as an exception.

SET_CLIENT_ID

This sets the worker ID in a job server so monitoring and reporting
commands can uniquely identify the various workers, and different
connections to job servers from the same worker.

Arguments:
- Unique string to identify the worker instance.

ALL_YOURS

Not yet implemented. This looks like it is used to notify a job
server that this is the only job server it is connected to, so
a job can be given directly to this worker with a JOB_ASSIGN and
no worker wake-up is required.

Arguments:
- None.


Worker Responses
----------------

These response types may only be sent to a worker:

NOOP

This is used to wake up a sleeping worker so that it may grab a
pending job.

Arguments:
- None.

NO_JOB

This is given in response to a GRAB_JOB request to notify the
worker there are no pending jobs that need to run.

Arguments:
- None.

JOB_ASSIGN

This is given in response to a GRAB_JOB request to give the worker
information needed to run the job. All communication about the
job (such as status updates and completion response) should use
the handle, and the worker should run the given function with
the argument.

Arguments:
- NULL byte terminated job handle.
- NULL byte terminated function name.
- Opaque data that is given to the function as an argument.

JOB_ASSIGN_UNIQ

This is given in response to a GRAB_JOB_UNIQ request and acts
just like JOB_ASSIGN but with the client assigned unique ID.

Arguments:
- NULL byte terminated job handle.
- NULL byte terminated function name.
- NULL byte terminated unique ID.
- Opaque data that is given to the function as an argument.

JOB_ASSIGN_ALL

This is given in response to a GRAB_JOB_ALL request and acts
just like JOB_ASSIGN_UNIQ but with the reducer returned.

Arguments:
- NULL byte terminated job handle.
- NULL byte terminated function name.
- NULL byte terminated unique ID.
- NULL byte terminated reducer.
- Opaque data that is given to the function as an argument.

Administrative Protocol
-----------------------

The Gearman job server also supports a text-based protocol to pull
information and run some administrative tasks. This runs on the same
port as the binary protocol, and the server differentiates between
the two by looking at the first character. If it is a NULL (\0),
then it is binary, if it is non-NULL, that it attempts to parse it
as a text command. The following commands are supported:

workers

This sends back a list of all workers, their file descriptors,
their IPs, their IDs, and a list of registered functions they can
perform. The list is terminated with a line containing a single
'.' (period). The format is:

FD IP-ADDRESS CLIENT-ID : FUNCTION ...

Arguments:
- None.

status

This sends back a list of all registered functions. Next to
each function is the number of jobs in the queue, the number of
running jobs, and the number of capable workers. The columns are
tab separated, and the list is terminated with a line containing
a single '.' (period). The format is:

FUNCTION\tTOTAL\tRUNNING\tAVAILABLE_WORKERS

Arguments:
- None.

maxqueue

This sets the maximum queue size for a function. If no size is
given, the default is used. If one size is given, it is applied to
jobs regardless of priority. If three sizes are given, the sizes
are used when testing high-priority, normal, and low-priority jobs,
respectively. A zero or negative size indicates no limit. This
command sends back a single line with "OK".

Arguments:
- Function name.
- Optional maximum queue size (to apply one maximum at all priorities), or
three optional maximum queue sizes (to enforce for high-, normal-, and
low-priority job submissions).

shutdown

Shutdown the server. If the optional "graceful" argument is used,
close the listening socket and let all existing connections
complete.

Arguments:
- Optional "graceful" mode.

version

Send back the version of the server.

Arguments:
- None.


The Perl version also has a 'gladiator' command that uses the
'Devel::Gladiator' Perl module and is used for debugging.


Binary Protocol Example
-----------------------

This example will step through a simple interaction where a worker
connects and registers for a function named "reverse", the client
connects and submits a job for this function, and the worker performs
this job and responds with a result. This shows every byte that needs
to be sent over the wire in order for the job to be run to completion.


Worker registration:

Worker -> Job Server
00 52 45 51 \0REQ (Magic)
00 00 00 01 1 (Packet type: CAN_DO)
00 00 00 07 7 (Packet length)
72 65 76 65 72 73 65 reverse (Function)


Worker check for job:

Worker -> Job Server
00 52 45 51 \0REQ (Magic)
00 00 00 09 9 (Packet type: GRAB_JOB)
00 00 00 00 0 (Packet length)

Job Server -> Worker
00 52 45 53 \0RES (Magic)
00 00 00 0a 10 (Packet type: NO_JOB)
00 00 00 00 0 (Packet length)

Worker -> Job Server
00 52 45 51 \0REQ (Magic)
00 00 00 04 4 (Packet type: PRE_SLEEP)
00 00 00 00 0 (Packet length)


Client job submission:

Client -> Job Server
00 52 45 51 \0REQ (Magic)
00 00 00 07 7 (Packet type: SUBMIT_JOB)
00 00 00 0d 13 (Packet length)
72 65 76 65 72 73 65 00 reverse\0 (Function)
00 \0 (Unique ID)
74 65 73 74 test (Workload)

Job Server -> Client
00 52 45 53 \0RES (Magic)
00 00 00 08 8 (Packet type: JOB_CREATED)
00 00 00 07 7 (Packet length)
48 3a 6c 61 70 3a 31 H:lap:1 (Job handle)


Worker wakeup:

Job Server -> Worker
00 52 45 53 \0RES (Magic)
00 00 00 06 6 (Packet type: NOOP)
00 00 00 00 0 (Packet length)


Worker check for job:

Worker -> Job Server
00 52 45 51 \0REQ (Magic)
00 00 00 09 9 (Packet type: GRAB_JOB)
00 00 00 00 0 (Packet length)

Job Server -> Worker
00 52 45 53 \0RES (Magic)
00 00 00 0b 11 (Packet type: JOB_ASSIGN)
00 00 00 14 20 (Packet length)
48 3a 6c 61 70 3a 31 00 H:lap:1\0 (Job handle)
72 65 76 65 72 73 65 00 reverse\0 (Function)
74 65 73 74 test (Workload)


Worker response for job:

Worker -> Job Server
00 52 45 51 \0REQ (Magic)
00 00 00 0d 13 (Packet type: WORK_COMPLETE)
00 00 00 0c 12 (Packet length)
48 3a 6c 61 70 3a 31 00 H:lap:1\0 (Job handle)
74 73 65 74 tset (Response)


Job server response to client:

Job Server -> Client
00 52 45 53 \0RES (Magic)
00 00 00 0d 13 (Packet type: WORK_COMPLETE)
00 00 00 0c 12 (Packet length)
48 3a 6c 61 70 3a 31 00 H:lap:1\0 (Job handle)
74 73 65 74 tset (Response)


At this point, the worker would then ask for more jobs to run (the
"Check for job" state above), and the client could submit more
jobs. Note that the client is full duplex and could have multiple
jobs being run over a single socket at the same time. The result
packets may not be sent in the same order the jobs were submitted
and instead interleaved with other job result packets.