Timeline

Adopting an index inserted every entry into a StringHashMap before answering anything: 255,167 keys on a 302MB store, to serve the one or two lookups a tree listing makes. Measured at 5.5ms of a 24ms open by building the map twice and taking the delta.

v3 appends entry_count little-endian u32 rids ordered by digest, and lookup binary-searches it -- ~18 comparisons against a quarter-million insertions. Opening tcl drops 24.0ms to 20.0ms; with the hardware crc32 change before it, 38.5ms to 20.0ms. Output byte-identical.

The directory carries RIDS and the entry records stay in scan order. Sorting the entries themselves would renumber every rid, and ancestry, phantom snapshots and the sync walk all read that numbering.

lookup consults the map first, then the directory: entries appended after adoption -- a tail resume past the index boundary, and every write on a scan-path store -- are only in the map. Every held-check that was reading index.get directly now goes through lookup, because intern runs during a tail resume and a miss there mints a duplicate entry for a digest already held.

A v2 sidecar is refused and rewritten rather than adopted, as v1 was: adopting one would leave lookup with neither a map nor a directory and answer null for held artifacts. Pinned by a test that downgrades a v3 blob and re-checksums it.

The tests pin what equality cannot: that the map is EMPTY after adoption and every digest still resolves, that a digest which is not held returns null rather than a neighbour -- the failure a binary search has and a map does not -- and that digests written out of sort order still resolve, so a directory that merely mirrored insertion order would fail.

Closes #145 closed check-in: 0d16bc966d user: dmestas tags: index-v3-145