Construction Benchmarks

Hardware and software

One Amazon EC2 r3.8xlarge instance:

• 32 cores of Xeon E5-2670v2
• 244 gigabytes of memory
• /: EBS General Purpose SSD (gp2), 128 GB
• /disk1: Instance Store SSD, 320 GB
• /disk2: Instance Store SSD, 320 GB
• /large_disk: EBS Throughput Optimized HDD (st1), 4 TB
• A recent version of VG

New hardware

The benchmarks are being updated to the following:

One Amazon EC2 i3.8xlarge instance:

• 32 cores of Xeon E5-2686 v4
• 244 gigabytes of memory
• /: EBS General Purpose SSD (gp2), 128 GB
• /large_disk: Instance Store: 4x 1.9 TB NVMe SSD in RAID 0
• A recent version of VG

Directory structure

• ~/vg: VG
• ~/data: Downloaded data
• ~/graphs: VG graphs
• ~/indexes: GBWT/GCSA2 indexes
• ~/logs: Construction logs

Data

The benchmarks are based on 1000 Genomes Project phase 3 data. In order to download the data, run the following in ~/graphs:

#!/bin/bash

# Get the reference
REFERENCE=hs37d5.fa
rm -f ${REFERENCE} ${REFERENCE}.gz
wget ftp://ftp.1000genomes.ebi.ac.uk/vol1/ftp/technical/reference/phase2_reference_assembly_sequence/${REFERENCE}.gz
gunzip ${REFERENCE}

# Get the variants
VARIANTS=ALL.wgs.phase3_shapeit2_mvncall_integrated_v5b.20130502.sites.vcf.gz
SHORTV=all.vcf.gz
rm -f ${SHORTV} ${SHORTV}.tbi
wget ftp://ftp.1000genomes.ebi.ac.uk/vol1/ftp/release/20130502/${VARIANTS}
wget ftp://ftp.1000genomes.ebi.ac.uk/vol1/ftp/release/20130502/${VARIANTS}.tbi
mv ${VARIANTS} ${SHORTV}
mv ${VARIANTS}.tbi ${SHORTV}.tbi

# Get the phasings for chromosomes 1-22
PREFIX=ALL.chr
SPREFIX=chr
SUFFIX=.phase3_shapeit2_mvncall_integrated_v5a.20130502.genotypes.vcf.gz
SSUFFIX=.vcf.gz
for i in $(seq 1 22; echo X; echo Y)
do
  NAME=${PREFIX}${i}${SUFFIX}
  SHORT=${SPREFIX}${i}${SSUFFIX}
  rm -f ${SHORT} ${SHORT}.tbi
  wget ftp://ftp.1000genomes.ebi.ac.uk/vol1/ftp/release/20130502/${NAME}
  wget ftp://ftp.1000genomes.ebi.ac.uk/vol1/ftp/release/20130502/${NAME}.tbi
  mv ${NAME} ${SHORT}
  mv ${NAME}.tbi ${SHORT}.tbi
done

# Get the phasings for chromosomes X and Y
wget ftp://ftp.1000genomes.ebi.ac.uk/vol1/ftp/release/20130502/ALL.chrX.phase3_shapeit2_mvncall_integrated_v1b.20130502.genotypes.vcf.gz
wget ftp://ftp.1000genomes.ebi.ac.uk/vol1/ftp/release/20130502/ALL.chrX.phase3_shapeit2_mvncall_integrated_v1b.20130502.genotypes.vcf.gz.tbi
mv ALL.chrX.phase3_shapeit2_mvncall_integrated_v1b.20130502.genotypes.vcf.gz chrX.vcf.gz
mv ALL.chrX.phase3_shapeit2_mvncall_integrated_v1b.20130502.genotypes.vcf.gz.tbi chrX.vcf.gz.tbi
wget ftp://ftp.1000genomes.ebi.ac.uk/vol1/ftp/release/20130502/ALL.chrY.phase3_integrated_v2a.20130502.genotypes.vcf.gz
wget ftp://ftp.1000genomes.ebi.ac.uk/vol1/ftp/release/20130502/ALL.chrY.phase3_integrated_v2a.20130502.genotypes.vcf.gz.tbi
mv ALL.chrY.phase3_integrated_v2a.20130502.genotypes.vcf.gz chrY.vcf.gz
mv ALL.chrY.phase3_integrated_v2a.20130502.genotypes.vcf.gz.tbi chrY.vcf.gz.tbi

Graph construction

We build VG graphs with variants embedded as alt paths. Node size is limited to 32 bases for better GCSA2 query performance. In order to build the graphs, run the following in ~/graphs:

#!/bin/bash

VG=~/vg/bin/vg
DATA=~/data
REFERENCE=${DATA}/hs37d5.fa
MAPPING=node_mapping

# Build the VG graphs
(seq 1 22; echo X; echo Y) | parallel -j 24 \
    "$VG construct -r $REFERENCE -v chr{}.vcf.gz -R {} -C -a > chr{}.vg"

# Harmonize the node ids
$VG ids -j -m $MAPPING  $(for i in $(seq 1 22; echo X; echo Y); do echo chr${i}.vg; done)
cp $MAPPING ${MAPPING}.backup

This will take several hours. The vg ids command produces an empty node mapping that is useful for some GCSA2 construction options.

GBWT construction

We run 12 construction jobs in parallel, starting from the largest chromosomes. The last jobs will finish soon after chromosome 2. Memory usage is roughly 1 GB for each 10 Mbp. Run the following in ~/indexes to build per-chromosome GBWT indexes.

#!/bin/bash

(echo X; seq 1 22; echo Y) | parallel -j 12 "./build_gbwt.sh {}"

Script build_gbwt.sh contains the following:

#!/bin/bash
# $1 - chromosome

VG=~/vg/bin/vg
DATA=~/data
GRAPHS=~/graphs
LOGS=~/logs
BASENAME=chr${1}

LOGFILE=${LOGS}/gbwt_${BASENAME}.log
rm -f $LOGFILE

START=$(date +%s)
echo "Start time: $START" >> $LOGFILE
echo >> $LOGFILE

$VG index -v ${DATA}/${BASENAME}.vcf.gz -G ${BASENAME}.gbwt -p ${GRAPHS}/${BASENAME}.vg 2>> $LOGFILE

STOP=$(date +%s)
echo >> $LOGFILE
echo "Finish time: $STOP" >> $LOGFILE
echo "Total time: $(($STOP-$START)) seconds" >> $LOGFILE

We can also merge the individual GBWT indexes into a single file. This takes around 10 minutes and 36 GB of memory using a single thread.

#!/bin/bash

MERGE=~/vg/deps/gbwt/merge_gbwt
LOGS=~/logs
OUTPUT=merged

LOGFILE=${LOGS}/gbwt_merge.log
rm -f $LOGFILE

$MERGE -f -o $OUTPUT $(for i in $(seq 1 22; echo X; echo Y); do echo chr${i}; done) >> $LOGFILE

Chromosome	Time (h)	GBWT (MB)	locate() (MB)	Total (MB)
1	29.44	658	711	1369
2	32.20	685	744	1429
3	27.07	562	596	1158
4	26.15	553	603	1156
5	24.17	504	543	1046
6	23.18	487	516	1003
7	21.80	476	485	962
8	21.44	466	463	929
9	17.31	391	387	778
10	18.05	420	415	835
11	18.49	416	416	833
12	17.40	407	405	812
13	13.35	309	304	613
14	12.19	293	284	577
15	11.27	277	265	542
16	12.39	291	270	561
17	10.30	255	235	490
18	10.29	239	228	467
19	8.16	202	183	385
20	8.18	193	180	373
21	4.99	132	120	252
22	4.78	133	122	256
X	14.46	396	326	722
Y	0.19	42	12	54
Total	34.32	8788	8814	17602
Merged	0.16	8849	9886	18736