Implementing a Central Quill Database in a Large Condor Installation Preston Smith Condor Week April 30, 2008

Background –BoilerGrid Motivation What works well What has been challenging What just doesn’t work Future directions Overview

Purdue Condor Grid (BoilerGrid) –Comprised of Linux HPC clusters, student labs, machines from academic department, and Purdue regional campuses 8900 batch slots today.. 14,000 batch slots in a few weeks Delivered over 10 million CPU-hours to high-throughput science to Purdue and national community through Open Science Grid and TeraGrid BoilerGrid

BoilerGrid - Growth

BoilerGrid - Results

Condor 6.9.4, –Quill can store information about all the execute machines and daemons in a pool –Quill now able to store job history and queue contents in a single, central database. Since December 2007, we’ve been working to store the state of BoilerGrid in a Quill installation A Central Quill Database

Why would we want to do such a thing?? –Research into the state of a large distributed system Several at Purdue, collaborators at Notre Dame –Failure analysis/prediction, smart scheduling, interesting reporting for machine owners –“events” table useful for user troubleshooting? –And one of our familiar gripes - usage reporting Structural biologists (see earlier today) like to submit jobs from their desks, too How can we access that job history to complete the picture of BoilerGrid’s usage? Motivation

Dell 2850 –2x 2.8GHz Xeons (hyperthreaded) –Postgres on 4-disk Ultra320 SCSI RAID-0 –5GB RAM The Quill Server

Getting at usage data! What works well quill=> select distinct scheddname,owner,cluster_id,proc_id,remotewallclocktime from jobs_horizontal_history where scheddname LIKE '%bio.purdue.edu%' LIMIT 10; scheddname | owner | cluster_id | proc_id | remotewallclocktime epsilon.bio.purdue.edu | jiang12 | | 0 | 345 epsilon.bio.purdue.edu | jiang12 | | 0 | 4456 epsilon.bio.purdue.edu | jiang12 | | 0 | 1209 epsilon.bio.purdue.edu | jiang12 | | 0 | 1197 epsilon.bio.purdue.edu | jiang12 | | 0 | 1064 epsilon.bio.purdue.edu | jiang12 | | 0 | 567 epsilon.bio.purdue.edu | jiang12 | | 0 | 485 epsilon.bio.purdue.edu | jiang12 | | 0 | 480 epsilon.bio.purdue.edu | jiang12 | | 0 | 509 epsilon.bio.purdue.edu | jiang12 | | 0 | 539 (10 rows)

Thousands of hosts pounding a Postgres database is non-trivial –Be sure to turn down QUILL_POLLING_PERIOD Default is 10s - we went down to 1 hour on execute machines –At some level, this is an exercise in tuning your Postgres server. Quick diversion into Postgres tuning What works, but is painful top - 13:45:30 up 23 days, 19:59, 2 users, load average: , , 428. Tasks: 804 total, 670 running, 131 sleeping, 3 stopped, 0 zombie Cpu(s): 94.6% us, 2.9% sy, 0.0% ni, 0.0% id, 0.0% wa, 0.4% hi, 2.2% si Mem: k total, k used, 36916k free, 10820k buffers Swap: k total, 68292k used, k free, k cached

Assuming that there’s enough disk bandwidth…. –In order to support 2500 simultaneous connections, one must turn up max_connections –If you turn up max_connections, you need ~400 bytes of shared memory per slot. Currently we have 2G of shared memory allocated Postgres

Then you’ll need to turn up shared_buffers –1G currently –Don’t forget fsm_pages… Postgres WARNING: relation "public.machines_vertical_history" contains more than "max_fsm_pages" pages with useful free space HINT: Consider compacting this relation or increasing the configuration parameter "max_fsm_pages".

So by now we can withstand the worker nodes reasonably well Add schedds –condor_history returns history from ALL schedds Bug fixed in –The execute machines create enough load that condor_q is sluggish –Added a 2nd quill database server just for job information What works, but is painful

If your daemons log a lot to sql.log files, but not writing to the database.. –Database down, etc –Your database is in a world of hurt while it tries to catch up.. What works, but is painful

Many Postgres tuning guides recommend a connection pooler if you need scads of connections –pgpool-II –Pgbouncer Tried both, Quill doesn’t seem to like it –It *did* reduce load…. What Hasn’t Worked But, often locked up the database (idle in transaction), and didn’t get anywhere

Throw hardware at the database! –Spindle count seems ok Not I/O bound (any more) –More memory = more connections 16GB? More? –More, faster CPUs We appear to be CPU-bound now Get latest multi-cores What can we do about it?

Contact Wisconsin and call for rescue What can we do about it? “Hey guys.. This is really hard on the old database” “Hmm. Let’s take a look.”

Todd, Greg, and probably others take a look: –Quill always hits the database, even for unchanged ads –Postgres backend does not prepare SQL queries before submitting Being fixed, Todd is optimistic –We’ll report with the results as soon as we have them What can Wisconsin do about it?

Reporting for users –Easy access to statistics about who ran on “my” machines. Mashups, web portals –Diagnostic tools to help users Troubleshooting, etc. Future Directions

Questions? The End

Backup slides

BoilerGrid - Results YearPool Size JobsHours Delivered Unique Users ,551346, ,7171,695, ,251,9815,527, ,611,8139,524, ??63 so far..