Setting Priorities for Nodes
The PRIORITY command assigns a priority to a DAG node (and to the HTCondor job(s) associated with the node). The syntax for PRIORITY is
PRIORITY <JobName | ALL_NODES> PriorityValue
The priority value is an integer (which can be negative). A larger numerical priority is better. The default priority is 0.
The node priority affects the order in which nodes that are ready (all
of their parent nodes have finished successfully) at the same time will
be submitted. The node priority also sets the node job’s priority in the
queue (that is, its
JobPrio attribute), which affects the order in
which jobs will be run once they are submitted (see
Job Priority for more
information). The node priority only affects the
order of job submission within a given DAG; but once jobs are submitted,
JobPrio value affects the order in which they will be run
relative to all jobs submitted by the same user.
Sub-DAGs can have priorities, just as “regular” nodes can. (The priority of a sub-DAG will affect the priorities of its nodes: see “effective node priorities” below.) Splices cannot be assigned a priority, but individual nodes within a splice can be assigned priorities.
Note that node priority does not override the DAG dependencies. Also note that node priorities are not guarantees of the relative order in which nodes will be run, even among nodes that become ready at the same time - so node priorities should not be used as a substitute for parent/child dependencies. In other words, priorities should be used when it is preferable, but not required, that some jobs run before others. (The order in which jobs are run once they are submitted can be affected by many things other than the job’s priority; for example, whether there are machines available in the pool that match the job’s requirements.)
PRE scripts can affect the order in which jobs run, so DAGs containing PRE scripts may not submit the nodes in exact priority order, even if doing so would satisfy the DAG dependencies.
Node priority is most relevant if node submission is throttled (via the -maxjobs or -maxidle command-line arguments or the DAGMAN_MAX_JOBS_SUBMITTED or DAGMAN_MAX_JOBS_IDLE configuration variables), or if there are not enough resources in the pool to immediately run all submitted node jobs. This is often the case for DAGs with large numbers of “sibling” nodes, or DAGs running on heavily-loaded pools.
Adding PRIORITY for node C in the diamond-shaped DAG:
# File name: diamond.dag
JOB A A.condor
JOB B B.condor
JOB C C.condor
JOB D D.condor
PARENT A CHILD B C
PARENT B C CHILD D
RETRY C 3
PRIORITY C 1
This will cause node C to be submitted (and, mostly likely, run) before node B. Without this priority setting for node C, node B would be submitted first because the “JOB” statement for node B comes earlier in the DAG file than the “JOB” statement for node C.
Effective node priorities
The “effective” priority for a node (the priority controlling the order in which nodes are actually submitted, and which is assigned to JobPrio) is the sum of the explicit priority (specified in the DAG file) and the priority of the DAG itself. DAG priorities also default to 0, so they are most relevant for sub-DAGs (although a top-level DAG can be submitted with a non-zero priority by specifying a -priority value on the condor_submit_dag command line). This algorithm for calculating effective priorities is a simplification introduced in version 8.5.7 (a node’s effective priority is no longer dependent on the priorities of its parents).
Here is an example to clarify:
# File name: priorities.dag
JOB A A.sub
SUBDAG EXTERNAL B SD.dag
PARENT A CHILD B
PRIORITY A 60
PRIORITY B 100
# File name: SD.dag
JOB SA SA.sub
JOB SB SB.sub
PARENT SA CHILD SB
PRIORITY SA 10
PRIORITY SB 20
In this example (assuming that priorities.dag is submitted with the default priority of 0), the effective priority of node A will be 60, and the effective priority of sub-DAG B will be 100. Therefore, the effective priority of node SA will be 110 and the effective priority of node SB will be 120.
The effective priorities listed above are assigned by DAGMan. There is no way to change the priority in the submit description file for a job, as DAGMan will override any priority command placed in a submit description file (unless the effective node priority is 0; in this case, any priority specified in the submit file will take effect).