482ddb3d1a4e718d508df96498266692ce16eac0
7 Commits
| Author | SHA1 | Message | Date | |
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A.Shakhmatov
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fc611a2c64 |
commands: $project computes, renames and narrows
The last three cases of the corpus, which is now 70 pass / 0 fail -- every
answer byte-identical to mongod 8.3.7 across the accumulators, the expressions
and the document stages.
The fix turned out to need nothing from `query.project`, which `find` shares
and which I had expected to have to rewrite. A nested spec *is* a dotted path:
`{n: {x: 1}}` and `{"n.x": 1}` are the same projection, and dotted paths are
something the existing projection already narrows correctly. So `$project` is
flattened into inclusion/exclusion flags plus a list of computed fields, and
both halves reuse machinery that was already there -- `query.project` for the
flags, `set_path` from the document stages for the computed fields. A bare path
(`{value: "$a"}`) is a rename, which is a computed field like any other.
Both shapes used to read as *falsy*, which flipped the whole projection into
its exclusion branch and returned the entire document minus the field. That was
recorded during M2 as broken rather than unimplemented; this is the fix it was
waiting for.
One case `query.project` genuinely cannot express, so it is built directly: a
projection that only computes keeps `_id` and nothing else, and with no non-`_id`
flag that function reads the spec as an exclusion and returns everything. It
cost two failures and a `id_only` flag to find, which is what a recorded corpus
is for -- the answer is obvious once seen and not before.
`$project` now goes through the same `Rewrite` path as `$addFields`, `$unset`,
`$replaceRoot` and `$unwind`, so its own branch is gone. Its refusal shrank to
the one shape mongod also refuses, mixing inclusion with exclusion, judged on
the flattened flags so a nested spec is treated like a dotted one.
191/191 unit tests in ReleaseFast and ReleaseSafe, 83/83 fuzz, e2e 49, e2e2
concurrent, e2e3 16, e2e4 17, e2e6 72, e2e7 86, crud corpus unchanged at
201/90/196.
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A.Shakhmatov
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1a5386ff00 |
commands: the stages that rewrite a document
`$addFields`, `$set`, `$unset`, `$replaceRoot` and `$unwind`. The corpus goes
0 pass / 24 fail to 21 / 3, and the three left are `$project`'s computed
fields, renames and nested inclusions, which want the `query.project` that
`find` shares and are their own change.
**The design review was wrong about what this needed, and the corpus is what
settled it.** Tier 2 was scoped as a per-stage iterator on the grounds that
`$unwind` is 1->N and "there is no way to express that in a window over the
input". That was true of the window as it stood, and stopped being true the
moment `$project` was made to rebuild the stream instead of moving bounds over
it -- a stage that rebuilds can emit as many documents as it likes, or none. So
all five share one shape: read the window, build a new list, replace the
stream. No iterator, no rewrite.
What the recording settled, and what a hand-written test would have got wrong:
- `$addFields` whose expression resolves to nothing leaves the field out
entirely rather than setting it to null -- so `set_path` is only reached
when there is a value, and `eval_expr`'s absent/null distinction earns its
keep a second time.
- `$addFields: {"n.z": 1}` sets the nested path and keeps its siblings, and
an existing field is replaced *where it stands*, which is what makes the
stage "add or overwrite" rather than "append".
- `$unwind` drops a document whose field is missing or an empty array, keeps
one whose field is not an array *whole*, and numbers `includeArrayIndex`
from zero. Three separate behaviours where one guess would have covered
them all wrongly.
- `$replaceRoot` of a missing path and of a non-document are the same error,
40228.
`ReplaceRootNotDocument` joins `EvalError` rather than being reported at the
stage: it is a failure only a document can produce, which is the line that set
already draws.
191/191 unit tests in ReleaseFast and ReleaseSafe, 83/83 fuzz, e2e 49, e2e3 16,
e2e4 17, e2e6 72, e2e7 86, crud corpus unchanged at 201/90/196.
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A.Shakhmatov
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88ac010c3c |
tests/spec: record Tier 2's spec -- the stages that rewrite a document
24 cases for `$addFields`/`$set`, `$unset`, `$replaceRoot`, `$unwind` and
`$project`'s computed fields, recorded from mongod 8.3.7 before any of them is
written. The file starts at 0 pass / 24 fail, which is the honest number for
five stages this server does not have.
Eight things the recording settled, none of them guessable from the manual:
$addFields whose expression is missing the field is not added at all
$addFields: {"n.z": 1} sets the nested path, keeps siblings
$replaceRoot of missing or non-document error 40228
$unwind of an empty array or missing the document is dropped
$unwind of a non-array the document is kept whole
$unwind path without a $ error 28818
includeArrayIndex 0-based
$project: {n: {x: 1}} narrows it; a document without
`n` keeps only `_id`
That last one is the `query.project` gap recorded during M2 as broken rather
than unimplemented -- a nested inclusion currently reads as falsy and returns
the whole document minus the field. It now has a measured expectation to be
fixed against, in the corpus, rather than a note in a commit message.
Worth stating before the implementation: the design review expected Tier 2 to
need a per-stage iterator, on the grounds that `$unwind` is 1->N and "there is
no way to express that in a window over the input". That was true of the window
as it stood, and stopped being true when `$project` was made to rebuild the
stream -- a stage that rebuilds can emit any number of documents it likes. So
Tier 2 looks like five stages rather than a rewrite. The corpus is what will
say whether that holds.
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A.Shakhmatov
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37cfa863ee |
commands: the aggregation expression evaluator
The whole corpus is green: 46 pass, 0 fail, byte-identical to mongod 8.3.7 on
every case including all 27 expressions and the compound `_id` that was the
last accumulator failure.
Expressions are *compiled once per pipeline and evaluated per document*, and
that split is the point rather than an optimisation: it keeps the property M2's
refusals bought, which is that a pipeline that cannot be answered is refused
before a single document is read instead of half way through with part of the
work already reported. `Expr` is the compiled tree, `compile_expr` reports,
`eval_expr` cannot.
Nineteen operators: `$literal`, the five arithmetic ones, seven comparisons,
`$and`/`$or`/`$not`, `$cond` in both its forms, `$ifNull` and `$switch`. Plus
the two shapes that are not operators at all -- a compound document, which is
what a `$group` `_id` usually is, and an array.
Everything the corpus recorded, and none of it guessable:
- absent and a present null are *different* internally, because `$ifNull`
treats them alike and `$push` does not. Hence `?bson.Value` throughout,
where the obvious shortcut is to fold absent into `.null` at the boundary
and lose the distinction for good.
- arithmetic over absent or null is `null` -- not an error, not zero -- and
over a string is an error, 7157723.
- `$divide` by zero is 4848401, `$switch` with no branch and no default is
40069, and both are failures only a document can produce, so `EvalError`
exists and `report_eval_error` maps it.
- two operators in one expression document is 15983 and *not* `$group`'s
40238: mongod distinguishes an expression from an accumulator there.
- truthiness is MongoDB's, so `-5` is true and `0.0` is false.
- `$mod` follows the dividend's sign, so -5 mod 4 is -1.
- `$not` takes a bare argument as readily as a one-element array.
`compile_expr` and `compile_operator` call each other, so their error set is
written out rather than inferred -- Zig cannot infer a cycle, and the failure
mode is a "dependency loop" message that says nothing about expressions.
Three cases left the Tier 0 refusal test, because a compound `_id`, `$literal`
and a `$multiply` argument all work now. What is refused should be what is
missing, so an unknown operator and a wrong operand count took their place.
191/191 unit tests in ReleaseFast and ReleaseSafe, 83/83 fuzz, e2e 49, e2e2
concurrent, e2e3 16, e2e4 17, e2e6 72, e2e7 86, crud corpus unchanged at
201/90/196.
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A.Shakhmatov
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1c72aa8938 |
tests/spec: record the expression evaluator's spec from mongod
27 cases, recorded before a line of the evaluator is written, which is the
whole point of having built the recorder first: the expectations come from
mongod 8.3.7 rather than from what the implementation is about to do.
The corpus reads 1 pass / 26 fail, and the one pass is the unknown-operator
refusal M2 already answers correctly. Expressions are exercised through
`$group` because `_id` and the accumulator arguments are the only expression
positions that exist until `$addFields` and `$project`'s computed fields land;
testing them anywhere else would be testing a stage that is not there.
Ten things the recording settled that guessing would have got wrong:
$add over a missing field or null null -- not an error, and not 0
$add over a string error 7157723
$divide by zero error 4848401
$mod of -5 by 4 -1, the dividend's sign
$lt of a number and a string true, canonical type order
$and over -5 truthy
$not of a missing field true
$switch, no branch and no default error 40069
two operators in one expression error 15983, *not* $group's 40238
$subtract with one operand error 16020
The six error codes are in `ErrorCode` already, so the evaluator's refusals and
its runtime failures have somewhere measured to land. The evaluator itself is
the next commit and is not started.
191/191 unit tests, crud corpus unchanged at 201/90/196.
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A.Shakhmatov
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76afa75efe |
commands: the $group accumulators
Nine of them -- `$sum`, `$avg`, `$min`, `$max`, `$first`, `$last`, `$push`,
`$addToSet`, `$count` -- and the corpus goes 9 pass / 10 fail to 18 pass /
1 fail. The one left is the compound `_id`, which needs the expression
evaluator.
Landed before that evaluator, against the tier order the design review set
out, and the corpus is why: every one of these takes a single value per
document, a path or a constant, so nine of its ten failures turned out to be
reachable without one. `classify_expr` already produced exactly that value.
What the recording caught, which is the argument for measuring expectations
rather than writing them:
- `$avg` over a group with no numeric value is **null**, not `0`. A divisor
that counted documents rather than numbers would pass every test anybody
would think to write by hand, and be wrong on the one group that matters.
- `$min`/`$max` compare across types in canonical BSON order, so the maximum
of `30`, `7` and `"not a number"` is the string.
- `$push` skips an absent field but would push an explicit null, so "resolved
to nothing" and "resolved to null" cannot be the same value internally --
which is why the accumulators take `?bson.Value` and not `.null`.
- `$first`/`$last` follow input order, including when the value is absent:
`$last` of a missing field is null, not the last present one.
`AccState` is one struct rather than a union: the fields are small and every
site already switches on the kind, so a union would add a tag test where a
switch was going to be anyway. Its arrays are the gpa's, the values inside them
the reply arena's -- they outlive the group and travel with the documents.
`numeric_value` is the int32-or-double narrowing MongoDB reports, shared now
between the accumulators and `cmd_aggregate`'s count fast path. It was written
twice before; a divergence between them would make `countDocuments` disagree
with the pipeline it is a shortcut for.
`$avg` and `$push` came out of the Tier 0 refusal test, replaced by
`$stdDevPop` and `$mergeObjects`. The refusal is a property of what is missing
rather than of a list, and the test should read that way.
191/191 unit tests in ReleaseFast and ReleaseSafe, 83/83 fuzz, e2e 49, e2e3 16,
e2e4 17, e2e6 72, e2e7 86, crud corpus unchanged at 201/90/196.
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A.Shakhmatov
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3044a38d1c |
tests/spec: an aggregation corpus, recorded from mongod
M2.5's gate, built before the milestone it gates -- the same order that put
`expectEvents` before the free list in M1 and Tier 0 before everything in M2.
`mongodb/specifications` has no aggregation suite, which is amendment A6's
central finding, so this milestone has to bring its own. The hazard in a corpus
we author is obvious and fatal: it can encode our own bugs as expectations and
then agree with us forever. So the split is enforced by the tooling.
`sources/*.json` holds documents and pipelines and nothing else; `record.js`
asks a real mongod 8.3.7 what each pipeline answers and writes the unified-
format file from the reply. Inputs authored, expectations measured -- the
discipline that corrected three assumptions in M1's session work and every
error code in M2, where the alternative would have shipped both times.
No second runner. `run.js --suite-dir` points the existing one somewhere else,
so the entity model, the matchers, the skip accounting and `expectEvents` come
for free; a second runner would drift from the first exactly where it mattered.
`--scorecard` is refused with `--suite-dir`, because `scorecard.txt` is the crud
corpus's record and the milestones are compared against it -- writing it from an
unrelated run would replace that record silently.
Errors record the code and not the message: message text is mongod's to change
between releases. Group pipelines end in a `$sort`, because group output order
is unspecified and a case depending on it would fail for the wrong reason on
either server.
The first source covers `$group`: nine accumulators including the edge cases
that decide an implementation -- `$avg` over a group whose values are not
numbers, `$min` of a field no document has, `$push` skipping a missing field,
`$first`/`$last` against input order, grouping on an array, a compound `_id`.
Where it starts, run against the M2 tip:
group-accumulators.json 9 pass 10 fail 0 skip
The nine include the four refusals M2 added, which answer with mongod's own
codes -- so the corpus already confirms that half. The ten are the milestone.
The crud corpus is unchanged at 201/90/196.
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