Aleksey Shakhmatov
53f88e6d3b
`replaceOne`, `findOneAndReplace` and `bulkWrite`'s `replaceOne` all failed
with "bad update". `update.apply` rejected any update document whose first key
was not `$`-prefixed, so a replacement document -- which by definition has no
operators -- could not get through at all.
MongoDB decides on the first field and nothing else: `$`-prefixed means
operators, anything else means the document *is* the new content. An empty
document is a replacement too, and a legal one. `is_replacement` says which,
`apply_replacement` does the work, and because all three call sites already go
through `apply`, that one branch covers the update command, findAndModify and
the upsert builder.
What a replacement means, precisely:
- every field is replaced except `_id`, which is immutable and keeps its
position at the front, where it is stored and where the `_id_` index
descends on it;
- a replacement may restate the same `_id` but not a different one -- that
is `ImmutableId`, because otherwise a rewrite would silently change a
document's identity while the index entry kept the old key;
- when the target has no `_id` yet, the replacement supplies it. That is the
upsert path: `build_upsert_doc` seeds a document from the filter's
equalities, so `replaceOne({_id: 99}, {u: 1}, {upsert: true})` inserts
`{_id: 99, u: 1}` and not a generated ObjectId;
- a mixed document is refused from either side, rather than guessed at.
Two options on update specs are refused rather than ignored:
- `multi` with a replacement (FailedToParse). A replacement describes one
document; applying it to many would leave every match identical apart from
its `_id`.
- `sort`, a MongoDB 8.0 addition this server does not implement. Ignoring it
is the worst of the three answers -- `sort` chooses *which* match to write,
so the client would silently get a different document than it asked for.
spec scorecard 131 pass / 161 fail -> 161 pass / 131 fail
e2e.js 35 checks -> 45
Sixteen spec files improved and none regressed. The two `-sort` files briefly
did: they had been passing on their "server-side error" case, which our
"bad update" failure satisfied by accident, and passing for the wrong reason is
how a gap survives a scorecard.
Five mutations, each verified red: seeding the replacement from the old pairs,
dropping the `_id` comparison, dropping the `_id` a replacement supplies, and
removing the mixed-document guard from either loop.
Note `nModified` is still wrong for a write that changes nothing -- MongoDB
counts a document as modified only if applying the update altered it. That is
the remaining bulkWrite failure and is fixed next, separately.
End-to-end tests with the official MongoDB Node.js driver
These exercise MultiforaDB from a real driver over TCP: full CRUD, query operators, aggregation, error codes, concurrent clients, crash recovery, and the whole lifecycle including server restarts.
Setup
cd tests/e2e
npm init -y >/dev/null
npm install mongodb
Run
Most suites expect a server running on port 27020:
zig build
zig-out/bin/multiforadb --port 27020 --db /tmp/mfdb-e2e.log --ttl-sweep-secs 1 &
node tests/e2e/e2e.js # CRUD + operators + aggregate + errors (29 checks)
node tests/e2e/e2e2.js concurrent # 8 clients: 4 writers + 4 readers (2 checks)
node tests/e2e/e2e2.js crash-a # write 50 docs, then kill -9 the server
node tests/e2e/e2e2.js crash-b # restart and verify all 50 survived
node tests/e2e/e2e3.js # secondary indexes: unique/sparse/compound (16 checks)
node tests/e2e/e2e4.js # TTL indexes: expiry + rejected specs (15 checks)
e2e4.js needs the server started with --ttl-sweep-secs 1 (the default is
60 seconds); the other suites do not care about the flag.
e2e6.js is the full-lifecycle suite and is self-contained: it spawns its
own server on port 27220 with a fresh log, runs the whole feature surface,
restarts the server twice (graceful SIGTERM, then kill -9 mid-write) and
verifies everything survived:
node tests/e2e/e2e6.js # 73 checks, ~15 s, needs no running server
E2E6_PORT=27300 node tests/e2e/e2e6.js # different port if 27220 is taken
Rebuild with zig build after any change under src/ before restarting the
server: zig build test compiles the test binary only and leaves
zig-out/bin/multiforadb stale, so the suites keep running against the old
rules and report failures that the source no longer explains.
e2e2.js concurrent is safe to repeat against a running server (it drops its
collection first); crash-a/crash-b are two halves of one scenario.
Multi-GB collections: big.js
big.js is a load harness, not a pass/fail suite: it spawns a server, bulk
loads up to ~5 GB, and reports insert throughput, the compaction behavior,
server RSS, per-operation latencies, reopen (replay) time, and kill -9
durability.
node tests/e2e/big.js --quick # 268 MB smoke run
node tests/e2e/big.js --size 5g --doc-size 128k --oid --batch 200 \
--compact-threshold 2g # ~5 GB, 40k docs
Options: --size/--doc-size/--batch (k/m/g suffixes), --oid
(ObjectId _ids — see below), --index <field> (secondary index before
loading), --compact-threshold <bytes> (passed to the server),
--port, --keep (keep the db file).
Measured behavior (all documented in the top-level README):
- Build in ReleaseFast —
zig builddefaults to it; a Debug server is 10-200x slower on every path. - Insert throughput collapses under the default 16 MiB compaction
threshold: every ~16 MB of writes rewrites the whole log with one fsync
per record (O(n²) total). With
--compact-threshold 2gthe rate stays flat (hundreds of MB/s at 128 KB docs in ReleaseFast). Raise the threshold for bulk loads. findOne({_id})is O(1) only for ObjectId_ids. Integer_ids are serialization-ambiguous (int32/int64/double compare equal but hash differently), so the docs-map fast path is skipped and every lookup is a full scan. Use the driver's default ObjectId ids on big collections.- The engine holds everything in RAM: ~1-1.2x the data size at 128 KB docs (more at 16 KB docs, where per-document arena overhead dominates). A 5 GB collection needs roughly 6-7 GB of RAM.
- Reopen of a 5 GB log replays in ~10 s (ReleaseFast); every committed write survives kill -9.
Comparing against real MongoDB: compare.js + compare-run.sh
bash tests/e2e/compare-run.sh [size] [doc-size] # e.g. 1g 16k
Starts mongod (brew install mongodb-community) on :27018 and MultiforaDB
on :27019, runs the same driver workload against each (durable writes:
MultiforaDB fsyncs per command, mongod runs with j: true), measures kill -9
reopen for both, and prints a side-by-side table. compare.js alone runs
one side (see its --help-style header comment).
Iteration-to-iteration comparison: bench-run.sh + concurrent.js
bash tests/e2e/bench-run.sh [size] [doc-size] ["clients..."] # e.g. 1g 16k "1 4 8 16 32"
Runs the main suite (compare-run.sh) plus a concurrent durable-write
comparison (concurrent.js, N clients each doing sequential insertOne
with {w:1, j:true} — the group-commit path under real contention), then
writes a machine-readable, versioned report to
tests/e2e/results/bench-<timestamp>.txt and prints a diff of the
MultiforaDB numbers against the previous run (results/bench-latest.txt).
The report has [main] / [concurrency] / [meta] sections with
name<TAB>value rows; bench-run.sh 1g 16k reproduces the phase8 gate
(see results/phase8.txt).