[adamv-symbolica]

Adds benches/wiki_prefixes.rs, which times catamorphisms on a map holding every prefix of every English Wikipedia article title. In a head-to-head of the cata implementations in #31 and its merkle-cata predecessor, this was the real-world dataset where caching shared nodes under valued paths mattered most.

What it measures

The bench builds a PathMap<()> in which every non-empty prefix of every title in the English Wikipedia title dump holds a value. The dump used below has 19,359,924 titles, which give 173,370,009 values.

It builds that map twice:

• the first copy is timed as built, so no node in it is shared;
• the second is merkleized in place before timing. merkleize turns each repeated subtrie, such as the endings _(disambiguation) or _(album), into one shared node. Because every path holds a value, every shared node sits below a path that holds a value.

On each copy it times:

• map.val_count();
• map.read_zipper().into_cata_cached(f) and map.read_zipper().into_cata_jumping_cached(f), where f returns the sum of its children's results plus one if the path holds a value, so both return the number of values;
• map.read_zipper().hash().

It also times merkleize() in place on a freshly built map. Building the maps and dropping them are outside every timing.

Data

The dump is not committed (~110 MB download, ~400 MB unpacked):

curl -L https://dumps.wikimedia.org/enwiki/latest/enwiki-latest-all-titles-in-ns0.gz \
  | gunzip > benches/enwiki-latest-all-titles-in-ns0

The bench reads it from BENCH_DATA_DIR (default benches/, where the file name is now gitignored). Without the file it prints the command above and exits 0, so cargo bench and CI are unaffected. WIKI_TITLES=<n> keeps an evenly spaced sample of about n titles. A full run takes 7–10 minutes and peaks at 33–38 GB, so the bench is not in bench_ab.py's default set.

Results

AMD EPYC 9B45, one core, median of 5 samples. All three branches were built from one checkout and target directory and run on the same machine.

operation	map	master (4e1c424)	PR 31 head (3a4f241)	merkle-cata (2dae7d1)
val_count	as built	5.10 s	0.99 s	1.08 s
	merkleized	2.43 s	3.98 s	2.01 s
into_cata_cached	as built	5.29 s	0.99 s	1.48 s
	merkleized	7.96 s	3.95 s	2.38 s
into_cata_jumping_cached	as built	7.67 s	0.99 s	1.10 s
	merkleized	10.31 s	3.96 s	2.08 s
hash	as built	6.06 s	3.48 s	4.16 s
	merkleized	9.40 s	5.79 s	2.86 s
merkleize	fresh build	30.6 s	34.7 s	34.9 s