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Chromium Single Cell Gene Expression

Cluster Mode

Cluster mode is one of three primary ways of running Cell Ranger. To learn about the other approaches, please go to the computing options page.


Cell Ranger can be run in cluster mode, using SGE or LSF to run the stages on multiple nodes via batch scheduling. This allows highly parallelizable stages to utilize hundreds or thousands of cores concurrently, dramatically reducing time to solution.

Cluster Mode

Running pipelines in cluster mode requires the following:

  1. Cell Ranger is installed in the same location on all nodes of the cluster. For example, /opt/cellranger-3.1.0 or /net/apps/cellranger-3.1.0
  2. Cell Ranger pipelines are run on a shared file system accessible to all nodes of the cluster. NFS-mounted directories are the most common solution for this requirement.
  3. The cluster accepts both single-core and multithreaded (shared-memory) jobs.

Configuring Cluster Template

Installing the Cell Ranger software on a cluster is identical to installation on a local server. After confirming that the cellranger commands can run in single server mode, configure the job submission template that Cell Ranger uses to submit jobs to the cluster. Assuming Cell Ranger is installed to /opt/cellranger-3.1.0, the process is as follows.

Step 1. Navigate to the Martian runtime's jobmanagers/ directory which contains example jobmanager templates.

$ cd /opt/cellranger-3.1.0/martian-cs/v3.2.3/jobmanagers
$ ls
bsub.template.example  config.json  sge.template.example

Step 2. Make a copy of the cluster's example template (SGE or LSF) to either sge.template or lsf.template in the jobmanagers/ directory.

$ cp -v sge.template.example sge.template
`sge.template.example' -> `sge.template'
$ ls
bsub.template.example  config.json  sge.template  sge.template.example

The job submission templates contain a number of special variables that are substituted by the Martian runtime when each stage is submitted. Specifically, the following variables are expanded when a pipeline is submitting jobs to the cluster:

Variable Must be present? Description
__MRO_JOB_NAME__ Yes Job name composed of the sample ID and stage being executed
__MRO_THREADS__ No Number of threads required by the stage
__MRO_MEM_GB__
__MRO_MEM_MB__
No Amount of memory (in GB or MB) required by the stage
__MRO_MEM_GB_PER_THREAD__
__MRO_MEM_MB_PER_THREAD__
No Amount of memory (in GB or MB) required per thread in multi-threaded stages.
__MRO_STDOUT__
__MRO_STDERR__
Yes Paths to the _stdout and _stderr metadata files for the stage
__MRO_CMD__ Yes Bourne shell command to run the stage code

It is critical that the special variables listed as required are present in the final template you create. For more information on how the template should appear for a cluster, consult your cluster administrator or help desk.

Additional Template Considerations

Depending on which job scheduler you have, please select a tab below.

For SGE cluster, you MUST replace <pe_name> within the example template to reflect the name of the cluster's multithreaded parallel environment. To view a list of the cluster's parallel environments, use the qconf -spl command.

The most common modifications to the job submission template include adding additional lines to specify:

  1. The research group's queue. For example, #$ -q smith.q
  2. The account to which jobs will charge. For example, #$ -A smith_lab
The most common modifications to the job submission template include adding additional lines to specify:
  1. Your research group's queue. For example, #BSUB -q smith_queue
  2. The account to which your jobs will charge. For example, #BSUB -P smith_lab

Validating Template Configuration

To run a Cell Ranger pipeline in cluster mode, add the --jobmode=sge or --jobmode=lsf command-line option when using the cellranger commands. It is also possible to use --jobmode=<PATH>, where <PATH> is the full path to the cluster template file.

To validate that cluster mode is properly configured, follow the same validation instructions given for cellranger in the Installation page, but add --jobmode=sge or --jobmode=lsf.

$ cellranger mkfastq --run=./tiny-bcl --samplesheet=./tiny-sheet.csv --jobmode=sge
 
Martian Runtime - 3.1.0
 
Running preflight checks (please wait)...
2016-09-13 12:00:00 [runtime] (ready)           ID.HAWT7ADXX.MAKE_FASTQS_CS.MAKE_FASTQS.PREPARE_SAMPLESHEET
2016-09-13 12:00:00 [runtime] (split_complete)  ID.HAWT7ADXX.MAKE_FASTQS_CS.MAKE_FASTQS.PREPARE_SAMPLESHEET
...

Once the preflight checks are finished, check the job queue to see stages queuing up:

$ qstat
job-ID  prior   name       user         state submit/start at     queue                          slots ja-task-ID
-----------------------------------------------------------------------------------------------------------------
8675309 0.56000 ID.HAWT7AD jdoe         qw    09/13/2016 12:00:00 all.q@cluster.university.edu       1
8675310 0.55500 ID.HAWT7AD jdoe         qw    09/13/2016 12:00:00 all.q@cluster.university.edu       1

In the event of a pipeline failure, an error message is displayed.

[error] Pipestance failed. Please see log at:
HAWT7ADXX/MAKE_FASTQS_CS/MAKE_FASTQS/MAKE_FASTQS_PREFLIGHT/fork0/chnk0/_errors
 
Saving diagnostics to HAWT7ADXX/HAWT7ADXX.debug.tgz
For assistance, upload this file to 10x by running:
 
uploadto10x <your_email> HAWT7ADXX/HAWT7ADXX.debug.tgz

The _errors file contains a jobcmd error:

$ cat HAWT7ADXX/MAKE_FASTQS_CS/MAKE_FASTQS/MAKE_FASTQS_PREFLIGHT/fork0/chnk0/_errors
 
jobcmd error:
exit status 1

The most likely reason for this failure is an invalid job submission template. This occurs when the job submission via qsub or bsub commands failed.

The "tiny" dataset doesn't stress the cluster, so it's worthwhile to follow up with a more realistic test using one of our sample datasets.

Cluster Mode Mechanics

There are two subtle variants of running cellranger pipelines in cluster mode, each with their own pitfalls. Check with your cluster administrator to see which approach is compatible with your institution's setup.

  1. Run cellranger with --jobmode=sge on the head node. Cluster mode was originally designed for this use case. However, this approach leaves mrp and mrjob running on the head node for the duration of the pipeline, and some clusters impose time limits to prevent long running processes.
  2. Use a job script to submit a cellranger command with --jobmode=sge: With this approach, mrp and mrjob run on a cluster mode. However, the cluster must allow jobs to be submitted from a compute node to make this viable.

When cellranger is run in cluster mode, a single library analysis is partitioned into hundreds and potentially thousands of smaller jobs. The underlying Martian pipeline framework launches each stage job using the qsub or bsub commands when running on SGE or LSF cluster, respectively. As stage jobs are queued, launched, and completed, the pipeline framework tracks their status using the metadata files that each stage maintains in the pipeline output directory.

Like single server pipelines, cluster-mode pipelines can be restarted after failure. They maintain the same order of execution for dependent stages of the pipeline. All executed stage code is identical to single server mode, and the quantitative results are identical to the limit of each stage's reproducibility.

In addition, the Cell Ranger UI can still be used with cluster mode. Because the Martian pipeline framework runs on the node from which the command was issued, the UI will also run from that node.

Memory Requests and Consumption

Stages in the Cell Ranger pipelines each request a specific number of cores and memory to aid with resource management. These values are used to prevent oversubscription of the computing system when running pipelines in single server mode. The way CPU and memory requests are handled in cluster mode is defined by the following:

Depending on which job scheduler you have, select a tab below.

SGE supports requesting memory via the mem_free resource natively, although your cluster may have another mechanism for requesting memory. To pass each stage's memory request through to SGE, add an additional line to your sge.template that requests mem_free, h_vmem, h_rss, or the custom memory resource defined by your cluster:
$ cat sge.template
#$ -N __MRO_JOB_NAME__
#$ -V
#$ -pe threads __MRO_THREADS__
#$ -l mem_free=__MRO_MEM_GB__G
#$ -cwd
#$ -o __MRO_STDOUT__
#$ -e __MRO_STDERR__
 
__MRO_CMD__

Note that the h_vmem (virtual memory) and mem_free/h_rss (physical memory) represent two different quantities, and that Cell Ranger stages' __MRO_MEM_GB__ requests are expressed as physical memory. Using h_vmem in your job template may cause certain stages to be unduly killed if their virtual memory consumption is substantially larger than their physical memory consumption. It follows that we do not recommend using h_vmem.

LSF supports job memory requests through the -M and -R [mem=...] options, but these requests generally must be expressed in MB, not GB. As such, your LSF job template should use the __MRO_MEM_MB__ variable rather than __MRO_MEM_GB__. For example,
$ cat bsub.template
#BSUB -J __MRO_JOB_NAME__
#BSUB -n __MRO_THREADS__
#BSUB -o __MRO_STDOUT__
#BSUB -e __MRO_STDERR__
#BSUB -R "rusage[mem=__MRO_MEM_MB__]"
#BSUB -R span[hosts=1]
 
__MRO_CMD__

For clusters whose job managers do not support memory requests, it is possible to request memory in the form of cores via the --mempercore command-line option. This option scales up the number of threads requested via the __MRO_THREADS__ variable according to how much memory a stage requires.

For example, given a cluster with nodes that have 16 cores and 128 GB of memory (8 GB per core), the following pipeline invocation command

$ cellranger mkfastq --run=./tiny-bcl --samplesheet=./tiny-sheet.csv --jobmode=sge --mempercore=8

will issue the following resource requests:

As the final bullet point illustrates, this mode can result in wasted CPU cycles and is only provided for clusters that cannot allocate memory as an independent resource.

Every cluster configuration is different. If you are unsure of how your cluster resource management is configured, contact your cluster administrator or help desk.

Controlling Rate of Job Submissions

Some Cell Ranger pipeline stages are divided into hundreds of jobs. By default, the rate at which these jobs are submitted to the cluster is throttled to at most 64 at a time and at least 100ms between each submission to avoid running into limits on clusters which impose quotas on the total number of pending jobs a user can submit.

If your cluster does not have these limits or is not shared with other users, you can control how the Martian pipeline runner sends job submissions to the cluster by using the --maxjobs and --jobinterval parameters.

To increase the cap on the number of concurrent jobs to 200, use the --maxjobs parameter:

$ cellranger count --id=sample ... --jobmode=sge --maxjobs=200

You can also change the rate limit on how often the Martian pipeline runner sends submissions to the cluster. To add a five-second pause between job submissions, use the --jobinterval parameter:

$ cellranger count --id=sample ... --jobmode=sge --jobinterval=5000

The job interval parameter is in milliseconds. The minimum allowable value is 1.