HISAT2 question, index generation.

Question

[Johan Largo]

Hello everyone, I have a question. Perform a basic line of work for RNA-seq analysis. A question arose when I generated the famous index in Hisat2 using the .FASTA extension reference genome.

What is it means the information that Hisat2 throws at the end. E.g .:

Returning block of 361373920 for bucket 7
Exited GFM loop
fchr [A]: 0
fchr [C]: 702240333
fchr [G]: 1196389250
fchr [T]: 1690616654
fchr [$]: 2392715236
Exiting GFM :: buildToDisk ()
...
Headers:
    len: 2392715236
    gbwtLen: 2392715237
    nodes: 2392715237
    sz: 598178809
    gbwtSz: 598178810
    lineRate: 6
    offRate: 4
    offMask: 0xfffffff0
    ftabChars: 10
    eftabLen: 0
    eftabSz: 0
    ftabLen: 1048577
    ftabSz: 4194308
    offsLen: 149544703
    offsSz: 598178812
    lineSz: 64
    sideSz: 64
    sideGbwtSz: 48
    sideGbwtLen: 192
    numSides: 12462059
    numLines: 12462059
    gbwtTotLen: 797571776
    gbwtTotSz: 797571776
    reverse: 0
    linearFM: Yes

What does "fchr [A]: 0" mean? The "headers" to which they refer? In the manual it is not very clear what all this means. What is all that information? which one is useful there?

I hope they help me or if by chance the same questions have also been asked.