Split chromosome into smaller fragments to save memory when build xg and gcsa index.

Question

[李经纬]

I follow the tutorial to build index for each chromosome. This saves memory when build index. However, my pc run out of memory when building xg index even in this case. Is it possible to split chromosome into smaller fragments to further save memory when build xg and gcsa index? How to specify this in the -R option of vg construct?

[李经纬]

I have tried to index various chromosome sets.

• chrom1 only: Memory usage: 2.53022 GB.
• chrom1-10: Memory usage: 13.3299 GB.
• chrom1-20: Memory usage: 22.9164 GB.
• chrom1-35: Memory usage: 23.5126 GB.

The memory usage will increase when more chromosome is included.

[李经纬]

I use vg construct --region chrom:start-end to restrict graph to a chromosome region.

Answer 1

[Jordan M Eizenga]

I would say the answer is unfortunately no. It would be possible to make smaller individual XG indexes, but downstream subcommands in the VG toolkit do not support multiple XGs. In general, VG is designed mostly for HPC clusters and shared compute servers that have > 64 GB of RAM. It would be difficult to run VG on most consumer-grade PCs.