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Analysis efficiency. Andrei Gheata ALICE offline week 03 October 2012. Sources for improving analysis efficiency. The analysis flow involves mixed processing phases per event Reading event data from disk – sequential (!) De-serializing the event object hierarchy – sequential (!)

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Analysis efficiency

Analysis efficiency

Andrei Gheata

ALICE offline week 03 October 2012


Sources for improving analysis efficiency
Sources for improving analysis efficiency

  • The analysis flow involves mixed processing phases per event

    • Reading event data from disk – sequential (!)

    • De-serializing the event object hierarchy – sequential (!)

    • Processing the event - parallelizable

    • Cleaning the event structures - sequential

    • Writing the output – sequential but parallelizable

    • Merging the outputs – sequential but parallelizable

  • The efficiency of the analysis job:

    • job_eff = (tds+tproc+tcl)/ttotal

    • analysis_eff = tproc / ttotal

  • Time/event for different phases depending on

    many factors

    • Tread~ IOPS*event_size/read_throughput – to be minimized

      • Minimize event size, keep under control read throughput

    • Tds+Tcl~ event_size*n_branches – to be minimized

      • Minimize event size and complexity

    • Tproc= ∑wagonsTi – to be maximized

      • Maximize number of wagons and useful processing

    • Twrite= output_size/write_throughput – to be minimized

Event #p

Event #0

Event #1

Event #2

Event #0

Event #m

Event #2

Event #n

Event #0

Event #1

Event #2

Event #1

tread

  • tds

  • tproc

  • tcl

  • twrite

tmerge


Monitoring analysis efficiency
Monitoring analysis efficiency

  • Instrumentation at the level of TAlienFile and AliAnalysisManager

  • Collecting timing, data size transfers, efficiency for different stages

    • Correlated with site, SE, LFN, PFN

  • Collection of data per subjob, remote or local

    • mgr->SetFileInfoLog(“fileinfo.log”);

    • Already in action for LEGO trains


Monitored analysis info
Monitored analysis info

#################################################################

pfn /11/60343/578c4420-6178-11e1-9cd1-00266cfd8b68#AliAOD.root

url root://xrootd3.farm.particle.cz:1094//11/60343/578c4420-6178-11e1-9cd1-00266cfd8b68#AliAOD.root

se ALICE::Prague::SE

image 1

nreplicas 0

openstamp 1348559810

opentime 0.701

runtime 2836.503

filesize 668.547

readsize 671.568

throughput 0.237

#################################################################

pfn /13/34934/2ed51c74-618b-11e1-a1cc-63e6dd7c661e#AliAOD.root

url root://xrootd3.farm.particle.cz:1094//13/34934/2ed51c74-618b-11e1-a1cc-63e6dd7c661e#AliAOD.root

se ALICE::Prague::SE

image 1

nreplicas 0

openstamp 1348562662

opentime 1.484

runtime 3890.802

filesize 642.818

readsize 640.459

throughput 0.165

#summary#########################################################

train_name train

root_time 36865.630

root_cpu 2564.810

init_time 74.647

io_mng_time 34510.137

exec_time 2280.846

alien_site CERN

host_name lxbse13c04.cern.ch

Processed input files

Analysis info


Throughput plots
Throughput plots

  • A simple and intuitive way to present the results

  • Will allow diagnosing both the infrastructure & the analysis

Time [sec]

Throughput [MB/sec]

PFN1

PFN2

PFN3

PFN4

PFN5

execution

I/O

Initialization


Few numbers for an empty analysis
Few numbers for an empty analysis

L= number of concurrent processes running on the disk storage server

I/O latency is a killer for events with many branches

De-serialization is determinant for locally available data – it depends on the size, but ALSO on the complexity (number of branches)


The source of problems
The source of problems

  • Highly fragmented buffer queries over high latency network

    • Big number of buffers retrieved sequentially

  • No asynchronous reading or prefetching enabled in xrootd or elsewhere

  • ROOT provides the mechanism to compact buffers and read them async: TTreeCache

    • Not used until now

    • Now added in AliAnalysisManager


Reading improvement aod
Reading improvement AOD

  • AOD PbPb, JINR::SE (RTT=65ms to CERN)


Reading improvement aod1
Reading improvement AOD

  • AOD pp, LBL::SE (RTT=173ms to CERN)


Reading improvement mc
Reading improvement MC

  • ESD pp, CNAF::SE (RTT=20 ms to CERN)

  • ESD pp, CERN::EOS (RTT=0.3 ms)


What to do to get it
What to do to get it

  • For AOD or ESD data, nothing

    • Cache set by default to 100 MB, async read enabled

    • Size of cache can be tuned via:

      mgr->SetCacheSize(bytes)

  • For MC, the cache sizes for kinematics and TR will follow the manager setting

    • Don’t forget to use:

      mcHandler->SetPreReadMode(AliMCEventHandler::kLmPreRead)


To do s
To do’s

  • Feed analysis info to alimonitor DB

    • Provide info in real time about analysis efficiency and status of data flows

    • Point out site configuration and dispatching problems

  • TTreePerfStats-based analysis

    • Check how our data structures perform and pin down eventual problems


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