configuration module provides tools for reading and writing
configuration parameters that control the behavior of an experiment. To use the
configuration, first import the module and get the configuration object:
import dallinger config = dallinger.config.get_config()
You can then get and set parameters:
config.get("duration") config.set("duration", 0.50)
When retrieving a configuration parameter, Dallinger will look for the parameter
first among environment variables, then in a
config.txt in the experiment
directory, and then in the
.dallingerconfig file, using whichever value
is found first. If the parameter is not found, Dallinger will use the default.
Built-in configuration parameters, grouped into categories:
- Run the experiment in this mode. Options include
sandbox(MTurk sandbox), and
- Where to write logs.
- A number between 0 and 4 that controls the verbosity of logs, from
- What’s life without whimsy? Controls whether email notifications sent regarding various experiment errors are whimsical in tone, or more matter-of-fact.
- A boolean on whether recruitment should be automatic.
browser_exclude_ruleunicode - comma separated
- A set of rules you can apply to prevent participants with unsupported web browsers from participating in your experiment.
- The recruiter class to use during the experiment run. While this can be a
full class name, it is more common to use the class’s
nicknameproperty for this value; for example
multi. NOTE: when running in debug mode, the HotAir (
hotair) recruiter will always be used. The exception is if the
--botsoption is passed to
dallinger debug, in which case the BotRecruiter will be used instead.
recruitersunicode - custom format
When using multiple recruiters in a single experiment run via the
multisetting for the
recruitersallows you to specify which recruiters you’d like to use, and how many participants to recruit from each. The special syntax for this value is:
recruiters = [nickname 1]: [recruits], [nickname 2]: [recruits], etc.
For example, to recruit 5 human participants via MTurk, and 5 bot participants, the configuration would be:
recruiters = mturk: 5, bots: 5
Amazon Mechanical Turk Recruitment¶
- AWS access key ID.
- AWS access key secret.
- AWS region to use. Defaults to
- Obsolete. See
- A boolean which controls whether an experiment-specific qualification
(based on the experiment ID), and a group qualification (based on the value
group_name) will be assigned to participants by the recruiter. This feature assumes a recruiter which supports qualifications, like the
- Assign a named qualification to workers who complete a HIT.
qualification_blacklistunicode - comma seperated
- Comma-separated list of qualification names. Workers with qualifications in this list will be prevented from viewing and accepting the HIT.
- The title of the HIT on Amazon Mechanical Turk.
- The description of the HIT on Amazon Mechanical Turk.
- A comma-separated list of keywords to use on Amazon Mechanical Turk.
- How long in hours that your HIT remains visible to workers.
- How long in hours participants have until the HIT will time out.
- Controls whether this HIT is available only to MTurk workers in the U.S.
- Base payment in U.S. dollars. All workers who accept the HIT are guaranteed this much compensation.
- The percentage of past MTurk HITs that must have been approved for a worker to qualify to participate in your experiment. 1-100.
Preventing Repeat Participants¶
If you set a
assign_qualifications is also set to
true, workers who complete your HIT will be given an MTurk qualification for
group_name. In the future, you can prevent these workers from
participating in a HIT with the same
group_name by including that name in
qualification_blacklist configuration. These four configuration keys
work together to create a system to prevent recuiting workers who have already
completed a prior run of the same experiment.
See Email Notification Setup for a much more detailed explanation of these values and their use.
- The email address used as the recipient for error report emails, and the email displayed to workers when there is an error.
- An email address for use by Dallinger to send status emails.
- Hostname and port of a mail server for outgoing mail. Defaults to
- Username for outgoing mail host.
- Password for the outgoing mail host.
- URI of the Postgres database.
- Size of the database on Heroku. See Heroku Postgres plans.
- Heroku dyno type to use. See Heroku dynos types.
- Size of the redis server on Heroku. See Heroku Redis.
- Number of Heroku dynos to use for processing incoming HTTP requests. It is recommended that you use at least two.
- Number of Heroku dynos to use for performing other computations.
- IP address of the host.
- Port of the host.
- URL where notifications are sent. This should not be set manually.
- If the clock process is on, it will perform a series of checks that ensure the integrity of the database.
- The name of the Heroku team to which all applications will be assigned. This is useful for centralized billing. Note, however, that it will prevent you from using free-tier dynos.
- Multiplier used to determine the number of gunicorn web worker processes started per Heroku CPU count. Reduce this if you see Heroku warnings about memory limits for your experiment. Default is 1.5
Choosing configuration values¶
When running real experiments it is important to pick configuration variables that result in a deployment that performs appropriately.
The number of Heroku dynos that are required and their specifications can make a very large difference to how the application behaves.
- This configuration variable determines how many dynos are run to deal with
web traffic. They will be transparently load-balanced, so the more web dynos are
started the more simultaneous HTTP requests the stack can handle.
If an experiment defines the
channelvariable to subscribe to websocket events then all of these callbacks happen on the dyno that handles the initial
/launchPOST, so experiments that use this functionality heavily receive significantly less benefit from increasing
num_dynos_web. The optimum value differs between experiments, but a good rule of thumb is 1 web dyno for every 10-20 simultaneous human users.
- Workers are dynos that pull tasks from a queue and execute them in the background.
They are optimized for many short tasks, but they are also used to run bots which
are very long-lived. Each worker can run up to 20 concurrent tasks, however they
are co-operatively multitasked so a poorly behaving task can cause all others
sharing its host to block.
When running with bots, you should always pick a value of
num_dynos_worker` that is at least ``0.05*number_of_bots, otherwise it is guaranteed to fail. In practice, there may well be experiment-specific tasks that also need to execute, and bots are more performant on underloaded dynos, so a better heuristic is
- This determines how powerful the heroku dyno that’s started is. It applies to both
web and worker dyno types. The minimum recommended is
standard-1x, which should be sufficient for experiments that do not rely on real-time coordination, such as Bartlett (1932), stories. Experiments that require significant power to process websocket events should consider the higher levels,
performance-l. In all but the most intensive experiments, either
num_dynos_webshould be increased, not both.
- A larger value for this increases the number of connections available on the redis dyno.
This should be increased for experiments that make substantial use of websockets. Values
premium-14. It is very unlikely that values higher than
- The duration parameter determines the number of hours that an MTurk worker has to complete the experiment. Choosing numbers that are too short can cause people to refuse to work on a HIT. A deadline that is too long may give people pause for thought as it may make the task seem underpaid. Set this to be significantly above the total time from start to finish that you’d expect a user to take in the worst case.
- The amount of US dollars to pay for completion of the experiment. The higher this is, the easier it will be to attract workers.