Hello Guix, I've spent some time looking whether the manual database generation could be sped up by switching from compressing the manual pages with zstd instead of zlib, which is reported to be about 3.5 times faster to decompress.
I thought decompression would play a role because the hook is CPU-intensive and thousands of files (depending on your profile) need to be decompressed in order to be parsed. But my experiment suggests otherwise: switching from zlib to zstd currently wouldn't buy us any gain; and profiling the mandb-entries from (guix man-db) shows something like this (current, zlib compression): --8<---------------cut here---------------start------------->8--- scheme@(guix man-db)> ,profile (define a (mandb-entries "/gnu/store/jgc63dxvpd8zq0p8al71x07a02qj8i1b-man-pages-5.13/share/man")) % cumulative self time seconds seconds procedure 20.95 1.98 1.75 gdbm.scm:122:11 20.95 1.75 1.75 string-tokenize 19.37 3.61 1.62 set-procedure-property! 6.72 0.56 0.56 ice-9/eval.scm:604:6 4.35 0.36 0.36 %read-line 4.35 0.36 0.36 anon #xa8e0b0 2.77 0.23 0.23 apply-smob/1 1.58 11.51 0.13 ice-9/eval.scm:292:11 1.58 0.20 0.13 open-file 1.58 0.13 0.13 ice-9/eval.scm:333:13 1.19 0.20 0.10 ice-9/eval.scm:263:9 1.19 0.13 0.10 ice-9/eval.scm:297:11 0.79 0.66 0.07 ice-9/eval.scm:159:9 0.79 0.07 0.07 ice-9/eval.scm:187:12 0.79 0.07 0.07 ice-9/popen.scm:183:0:reap-pipes 0.79 0.07 0.07 stat 0.79 0.07 0.07 ice-9/eval.scm:273:7 0.79 0.07 0.07 make-custom-binary-input-port 0.79 0.07 0.07 anon #xa8e078 0.79 0.07 0.07 ice-9/eval.scm:123:11 0.40 0.76 0.03 ice-9/rdelim.scm:193:0:read-line 0.40 0.20 0.03 ice-9/ftw.scm:445:2:loop 0.40 0.17 0.03 zlib.scm:158:0:make-gzip-input-port 0.40 0.03 0.03 ice-9/eval.scm:182:7 0.40 0.03 0.03 ice-9/eval.scm:329:11 0.40 0.03 0.03 string-trim-both 0.40 0.03 0.03 ice-9/eval.scm:125:11 0.40 0.03 0.03 dup->fdes 0.40 0.03 0.03 ice-9/eval.scm:226:7 0.40 0.03 0.03 string<? 0.40 0.03 0.03 ice-9/eval.scm:330:13 0.40 0.03 0.03 equal? 0.40 0.03 0.03 ice-9/eval.scm:155:9 0.40 0.03 0.03 ice-9/eval.scm:124:11 0.40 0.03 0.03 regexp-exec 0.40 0.03 0.03 ice-9/eval.scm:417:6 0.40 0.03 0.03 zlib.scm:66:0 0.40 0.03 0.03 ice-9/ftw.scm:218:12:string=?@guile 0.00 10070.94 0.00 ice-9/boot-9.scm:220:5:map1 0.00 12.57 0.00 zlib.scm:217:0:call-with-gzip-input-port 0.00 8.37 0.00 <current input>:11:9 0.00 3.64 0.00 ice-9/eval.scm:586:29 0.00 2.05 0.00 %after-gc-thunk 0.00 2.05 0.00 anon #xa7d750 0.00 1.98 0.00 ice-9/eval.scm:212:12 0.00 1.46 0.00 string-map 0.00 0.36 0.00 %read-line 0.00 0.36 0.00 zlib.scm:99:4 0.00 0.20 0.00 ice-9/eval.scm:618:6 0.00 0.10 0.00 guix/build/utils.scm:476:0:find-files 0.00 0.10 0.00 ice-9/eval.scm:244:10 0.00 0.10 0.00 anon #xa7d6dc 0.00 0.10 0.00 ice-9/eval.scm:625:6 0.00 0.10 0.00 srfi/srfi-1.scm:452:2:fold 0.00 0.07 0.00 zlib.scm:87:4 0.00 0.07 0.00 ice-9/boot-9.scm:1971:6 0.00 0.03 0.00 sort 0.00 0.03 0.00 ice-9/eval.scm:263:9 0.00 0.03 0.00 guix/build/utils.scm:492:28 --- Sample count: 253 Total time: 8.368360886 seconds (5.356567327 seconds in GC) --8<---------------cut here---------------end--------------->8--- When rebuilding the man-pages package with zstd compressed manuals and using guile-zstd to read them, we instead get: --8<---------------cut here---------------start------------->8--- scheme@(guix man-db)> ,profile (define a (mandb-entries "/gnu/store/dsm4wkzgzq6i00xc765vpgdzb0aq99fa-man-pages-5.13/share/man")) % cumulative self time seconds seconds procedure 28.93 2.38 2.34 gdbm.scm:122:11 18.60 3.82 1.51 set-procedure-property! 12.81 1.04 1.04 string-tokenize 7.02 0.57 0.57 ice-9/eval.scm:604:6 4.55 0.37 0.37 make-bytevector 4.13 0.33 0.33 %read-line 3.31 0.27 0.27 anon #x1bb01e0 1.65 0.17 0.13 ice-9/eval.scm:263:9 1.65 0.13 0.13 stat 1.24 0.90 0.10 ice-9/rdelim.scm:193:0:read-line 1.24 0.10 0.10 ice-9/eval.scm:342:13 1.24 0.10 0.10 ice-9/eval.scm:125:11 1.24 0.10 0.10 regexp-exec 0.83 0.10 0.07 ice-9/eval.scm:155:9 0.83 0.07 0.07 ice-9/eval.scm:333:13 0.83 0.07 0.07 pointer->bytevector 0.83 0.07 0.07 anon #x1bb01a8 0.83 0.07 0.07 ice-9/eval.scm:187:12 0.83 0.07 0.07 string<? 0.83 0.07 0.07 get-bytevector-n! 0.41 11.92 0.03 zstd.scm:273:0:call-with-zstd-input-port 0.41 10.72 0.03 ice-9/eval.scm:292:11 0.41 1.91 0.03 ice-9/eval.scm:212:12 0.41 0.03 0.03 ice-9/eval.scm:123:11 0.41 0.03 0.03 ice-9/eval.scm:273:7 0.41 0.03 0.03 string-suffix? 0.41 0.03 0.03 ice-9/eval.scm:155:9 0.41 0.03 0.03 readdir 0.41 0.03 0.03 system/foreign.scm:188:20 0.41 0.03 0.03 ice-9/eval.scm:182:7 0.41 0.03 0.03 apply-smob/1 0.41 0.03 0.03 string-contains 0.41 0.03 0.03 ice-9/rdelim.scm:93:23:string-append@guile 0.41 0.03 0.03 equal? 0.41 0.03 0.03 close-port 0.41 0.03 0.03 ice-9/eval.scm:126:12 0.00 9965.18 0.00 ice-9/boot-9.scm:220:5:map1 0.00 8.10 0.00 <current input>:5:9 0.00 3.82 0.00 ice-9/eval.scm:586:29 0.00 2.38 0.00 anon #x1b9f6c0 0.00 2.38 0.00 %after-gc-thunk 0.00 1.57 0.00 string-map 0.00 0.57 0.00 ice-9/eval.scm:159:9 0.00 0.47 0.00 %read-line 0.00 0.47 0.00 zstd.scm:234:2:read! 0.00 0.44 0.00 zstd.scm:216:0:make-zstd-input-port 0.00 0.27 0.00 ice-9/ftw.scm:445:2:loop 0.00 0.17 0.00 srfi/srfi-1.scm:452:2:fold 0.00 0.13 0.00 ice-9/boot-9.scm:1971:6 0.00 0.13 0.00 ice-9/eval.scm:196:12 0.00 0.13 0.00 ice-9/eval.scm:618:6 0.00 0.13 0.00 guix/build/utils.scm:487:0:find-files 0.00 0.13 0.00 anon #x1b9f64c 0.00 0.13 0.00 ice-9/eval.scm:297:11 0.00 0.10 0.00 ice-9/eval.scm:244:10 0.00 0.10 0.00 system/foreign.scm:187:0:parse-c-struct 0.00 0.10 0.00 guix/build/utils.scm:503:28 0.00 0.07 0.00 ice-9/eval.scm:278:9 0.00 0.07 0.00 zstd.scm:208:4 0.00 0.07 0.00 filter 0.00 0.07 0.00 ice-9/eval.scm:625:6 0.00 0.07 0.00 sort 0.00 0.07 0.00 ice-9/eval.scm:259:9 0.00 0.03 0.00 open-file 0.00 0.03 0.00 close-port 0.00 0.03 0.00 ice-9/eval.scm:191:12 0.00 0.03 0.00 bytevector->pointer --- Sample count: 242 Total time: 8.104984533 seconds (5.253193735 seconds in GC) --8<---------------cut here---------------end--------------->8--- So, it seems the parsing of the manual files itself in Guile (to retrieve their name, synopsis, etc.) is what is using most of the time (CPU-bound). Perhaps this can be optimized? Maxim