A validator is a program that decides whether completed jobs are "valid". You must specify a validator for each application in your project, and include it in the <daemons> section of your project configuration file.
Validating a completed job has 2 parts:
- Syntax check: verify that its output files are present on the server and have the correct format.
- Replication check: if the job is replicated, compare its replicas. If a strict majority are found to be "equivalent", those replicas are considered valid and the rest are marked as invalid.
BOINC includes several "standard" validators:
- Marks a job as valid if its output files are present. Use this if all hosts are trusted. Not used with job replication.
- Marks a job as valid if its stderr output includes a string specified by the --stderr_substr command-line arg. Not used with job replication.
- Output files are equivalent if they agree byte for byte. This can be used if your application generates exactly matching results (either because it does no floating-point arithmetic, or because you use homogeneous redundancy). If output files are gzip archives, use the --is_gzip command-line arg. This will skip the gzip header when comparing files.
For a given application, you may want to define your own syntax check for output files, or your own notion of "equivalence" (for example, regarding floating-point numbers as equivalent if they agree within some tolerance). In such cases, you can develop a custom validator for the application.
A validator (either standard or custom) has the following command-line arguments:
- --app appname
- Name of the application
- [ --one_pass_N_WU N ]
- Validate at most N WUs, then exit
- [ --one_pass ]
- Make one pass through WU table, then exit
- [ --mod n i ]
- Process only WUs with (id mod n) == i. This option lets you run multiple instances of the validator for increased performance.
- [ --max_granted_credit X ]
- Grant no more than this amount of credit to a job.
- [ --update_credited_job ]
- For each valid result, create an entry in the credited_job database table. This lets you keep track of which user contributed to each WU, even if you use db_purge.
Options related to credit. Don't use these options in general. With no options, validators will grant credit in a fair way.
- [ --no_credit ]
- Don't grant credit (use this if you grant credit via trickle messages).
- [ --credit_from_runtime ]
- Grant credit proportional to (runtime * CPU FLOPS).
Use this if:
- the app has only single-threaded CPU versions, and
- the app's jobs do different amounts of computation on different hosts, e.g. if they exit after a fixed amount of time.
- [ --credit_from_wu ]
- Grant credits written in WU template. See CreditAlt and JobSubmission.