⚡ Bolt: Optimize row scanning and query execution allocations#95
Conversation
This patch introduces several high-impact optimizations to the "hot paths"
of the Rain ORM, specifically targeting query execution and result scanning.
1. Query Execution: Added a pre-calculated `args` slice to `compiledQuery`.
Standard queries without named placeholders now reuse this slice
instead of allocating a new `[]any` on every execution, reducing
point-lookup allocations by 1.
2. Direct Scanning: Optimized `scanRowsAgainstTableDirect` to skip
expensive `reflect.NewAt` and `item.Set` calls for "full scans"
where all columns are assigned via `unsafe.Pointer` offsets. This
saves exactly one `reflect.Value` allocation per row in bulk scans.
3. Cache Scanning: Updated `scanCachedRowsAgainstTable` to pre-allocate
the destination slice with correct capacity, eliminating multiple
re-allocations and copies during the growth loop.
4. Correctness: Fixed `needsTargetValue` detection in the scan plan to
ensure a valid target `reflect.Value` is provided for types that
are not yet fast-pathed in the direct address scanner.
⚡ Bolt: Reduces allocations by ~1 per query and ~1 per row in bulk scans.
Co-authored-by: cungminh2710 <8063319+cungminh2710@users.noreply.github.com>
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Greptile SummaryThis PR reduces per-query and per-row allocations across three areas: pre-computing a flat
Confidence Score: 4/5Safe to merge; all optimized paths are logically correct and the latent needsTargetValue bug fix improves correctness for struct-typed direct fields. The core scan and compile logic is correct across all four isFullScan × needsTargetValue combinations, and the index-based named-placeholder filling in bind() is accurate. The two observations are about the shared backing array returned by literalArgs()/bind() and the implicit aliasing assumption in wrapExistsCompiled — neither causes a defect today, but they lower the margin for safe future modifications to those code paths. pkg/rain/query_compile.go deserves a second look for the shared-slice ownership contract on the literalArgs()/bind() return values, particularly in the context of PreparedSelectQuery reuse.
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| Filename | Overview |
|---|---|
| pkg/rain/query_compile.go | Adds a pre-computed args []any field to compiledQuery; literalArgs() and non-named bind() now return this slice directly instead of a fresh copy, saving one allocation per execution. Named-placeholder bind() still allocates a copy and fills named slots by index. Logic is correct but the shared backing array is a subtle ownership change worth documenting. |
| pkg/rain/model.go | Two optimizations: (1) skips reflect.NewAt in scanRowsAgainstTableDirect when no otherCols exist, with a correct fallback to still zero non-full-scan structs; (2) pre-allocates the result slice in scanCachedRowsAgainstTable, also fixing an inconsistency where the cached path would append to an existing target slice while the live-scan path started fresh. Also fixes latent bug where needsTargetValue was not set for otherCols fields that happened to have canUseOffset=true. |
| pkg/rain/query_select.go | wrapExistsCompiled simplified from explicit deep-copy to in-place SQL string mutation on a value-receiver copy; correct for the single call site but the function now implicitly assumes the caller does not retain the original compiled value after the call. |
Flowchart
%%{init: {'theme': 'neutral'}}%%
flowchart TD
A[compiledQuery created] --> B{hasNames?}
B -- Yes --> C[argPlan = deep copy of c.argPlan
args = make slice, fill literal slots]
B -- No --> D[argPlan = nil
args = make slice, fill all as literals]
C --> E[bind called with PreparedArgs]
E --> F[bound = copy of args
fill named slots by index i
return bound NEW allocation]
D --> G[literalArgs / bind no-names]
G --> H[return q.args directly
no copy — shared backing array]
subgraph scanRowsAgainstTableDirect [scanRowsAgainstTableDirect - per row]
I{needsTargetValue?} -- Yes --> J[reflect.NewAt + Elem
obtain targetVal]
J --> K{isFullScan?}
K -- No --> L[targetVal.Set zeroElem]
K -- Yes --> M[skip zero]
I -- No --> N{isFullScan?}
N -- No --> O[reflect.NewAt + Set zeroElem
discard Value]
N -- Yes --> P[skip entirely
save 1 alloc per row]
M & L & O & P --> Q[scanDirectRowAddr ptr targetVal plan scratch]
end
Prompt To Fix All With AI
Fix the following 2 code review issues. Work through them one at a time, proposing concise fixes.
---
### Issue 1 of 2
pkg/rain/query_compile.go:41-46
**Shared backing array returned to callers**
`literalArgs()` and the `!q.hasNames` branch of `bind()` now return `q.args` directly instead of a fresh copy. For `PreparedSelectQuery`, the `compiledQuery` is stored permanently and reused across many calls — every invocation of `Scan`, `Count`, or `Exists` receives the same backing array. Today all call sites only read the slice (cache-key hashing, variadic spread to `QueryContext`), so concurrent reads are safe. However, a future change that modifies the returned slice (e.g., appending a tenant ID or an extra bound value) before passing it to the driver would silently corrupt the prepared query's `args` for every subsequent call, because the original never creates a defensive copy anymore. The previous code always returned an independent slice, which kept this footgun impossible.
### Issue 2 of 2
pkg/rain/query_select.go:977-979
**Silent slice aliasing after removing explicit argPlan copy**
The previous `wrapExistsCompiled` made an explicit deep copy of `argPlan` so that the returned `compiledQuery` had no shared mutable state with its source. The new code mutates and returns a value-type copy, meaning `argPlan` and `args` are still backed by the same arrays as the `compiled` passed in. In the one call site (`compileExists`), `compiled` is a local that immediately goes out of scope, so there is no live aliasing today. But the function signature accepts any `compiledQuery` by value, and a future caller that retains the original `compiled` alongside the returned exists-variant would silently share mutable slice state between the two. A comment documenting the ownership assumption (caller must not use the original after this call) would prevent a subtle future regression.
Reviews (1): Last reviewed commit: "perf(rain): optimize row scanning and qu..." | Re-trigger Greptile
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| if !q.hasNames { | ||
| bound := make([]any, 0, len(q.argPlan)) | ||
| for _, arg := range q.argPlan { | ||
| bound = append(bound, arg.value) | ||
| } | ||
| if len(args) > 0 { | ||
| return nil, fmt.Errorf("rain: unexpected prepared args for query without placeholders") | ||
| } | ||
| return bound, nil | ||
| return q.args, nil | ||
| } |
There was a problem hiding this comment.
literalArgs() and the !q.hasNames branch of bind() now return q.args directly instead of a fresh copy. For PreparedSelectQuery, the compiledQuery is stored permanently and reused across many calls — every invocation of Scan, Count, or Exists receives the same backing array. Today all call sites only read the slice (cache-key hashing, variadic spread to QueryContext), so concurrent reads are safe. However, a future change that modifies the returned slice (e.g., appending a tenant ID or an extra bound value) before passing it to the driver would silently corrupt the prepared query's args for every subsequent call, because the original never creates a defensive copy anymore. The previous code always returned an independent slice, which kept this footgun impossible.
Prompt To Fix With AI
This is a comment left during a code review.
Path: pkg/rain/query_compile.go
Line: 41-46
Comment:
**Shared backing array returned to callers**
`literalArgs()` and the `!q.hasNames` branch of `bind()` now return `q.args` directly instead of a fresh copy. For `PreparedSelectQuery`, the `compiledQuery` is stored permanently and reused across many calls — every invocation of `Scan`, `Count`, or `Exists` receives the same backing array. Today all call sites only read the slice (cache-key hashing, variadic spread to `QueryContext`), so concurrent reads are safe. However, a future change that modifies the returned slice (e.g., appending a tenant ID or an extra bound value) before passing it to the driver would silently corrupt the prepared query's `args` for every subsequent call, because the original never creates a defensive copy anymore. The previous code always returned an independent slice, which kept this footgun impossible.
How can I resolve this? If you propose a fix, please make it concise.Note: If this suggestion doesn't match your team's coding style, reply to this and let me know. I'll remember it for next time!
| func wrapExistsCompiled(compiled compiledQuery) (compiledQuery, error) { | ||
| existsQuery := compiledQuery{ | ||
| sql: "SELECT EXISTS(" + compiled.sql + ")", | ||
| argPlan: make([]compiledArg, len(compiled.argPlan)), | ||
| hasNames: compiled.hasNames, | ||
| } | ||
| copy(existsQuery.argPlan, compiled.argPlan) | ||
| return existsQuery, nil | ||
| compiled.sql = "SELECT EXISTS(" + compiled.sql + ")" | ||
| return compiled, nil |
There was a problem hiding this comment.
The previous wrapExistsCompiled made an explicit deep copy of argPlan so that the returned compiledQuery had no shared mutable state with its source. The new code mutates and returns a value-type copy, meaning argPlan and args are still backed by the same arrays as the compiled passed in. In the one call site (compileExists), compiled is a local that immediately goes out of scope, so there is no live aliasing today. But the function signature accepts any compiledQuery by value, and a future caller that retains the original compiled alongside the returned exists-variant would silently share mutable slice state between the two. A comment documenting the ownership assumption (caller must not use the original after this call) would prevent a subtle future regression.
Prompt To Fix With AI
This is a comment left during a code review.
Path: pkg/rain/query_select.go
Line: 977-979
Comment:
**Silent slice aliasing after removing explicit argPlan copy**
The previous `wrapExistsCompiled` made an explicit deep copy of `argPlan` so that the returned `compiledQuery` had no shared mutable state with its source. The new code mutates and returns a value-type copy, meaning `argPlan` and `args` are still backed by the same arrays as the `compiled` passed in. In the one call site (`compileExists`), `compiled` is a local that immediately goes out of scope, so there is no live aliasing today. But the function signature accepts any `compiledQuery` by value, and a future caller that retains the original `compiled` alongside the returned exists-variant would silently share mutable slice state between the two. A comment documenting the ownership assumption (caller must not use the original after this call) would prevent a subtle future regression.
How can I resolve this? If you propose a fix, please make it concise.
|
@jules Fix the following 2 code review issues. Work through them one at a time, proposing concise fixes. Issue 1 of 2pkg/rain/query_compile.go:41-46
Issue 2 of 2pkg/rain/query_select.go:977-979 The previous |
I've addressed both issues:
Thank you for the detailed catch on the shared array state! |
This patch introduces several high-impact optimizations to the "hot paths"
of the Rain ORM, specifically targeting query execution and result scanning.
1. Query Execution: Added a pre-calculated `args` slice to `compiledQuery`.
Standard queries now return a fresh copy of this pre-calculated slice,
avoiding the overhead of rebuilding from metadata on every execution
while maintaining defensive safety.
2. Direct Scanning: Optimized `scanRowsAgainstTableDirect` to skip
expensive `reflect.NewAt` calls for "full scans" where all columns
are assigned via `unsafe.Pointer` offsets. This saves exactly one
`reflect.Value` allocation per row in bulk scans.
3. Cache Scanning: Updated `scanCachedRowsAgainstTable` to pre-allocate
the destination slice with correct capacity, eliminating multiple
re-allocations and copies during result collection.
4. Correctness: Fixed `needsTargetValue` detection in the scan plan to
ensure a valid target `reflect.Value` is provided for all field types.
⚡ Bolt: Reduces allocations by ~1 per query and ~1 per row in bulk scans.
Co-authored-by: cungminh2710 <8063319+cungminh2710@users.noreply.github.com>
1 participant
Optimized row scanning and query execution to reduce allocations.
argsincompiledQuerysaves 1 allocation per execution.reflect.NewAtin bulk "full scans" saves 1 allocation per row.PR created automatically by Jules for task 11501825494451725442 started by @cungminh2710