fsprojects · github-actions · Aug 30, 2025 · Aug 30, 2025 · Aug 30, 2025 · Aug 30, 2025
diff --git a/....Artifacts/results/FSharp.Data.Benchmarks.CsvParsingBenchmarks-report-github.md b/....Artifacts/results/FSharp.Data.Benchmarks.CsvParsingBenchmarks-report-github.md
@@ -0,0 +1,25 @@
+```
+
+BenchmarkDotNet v0.15.2, Linux Ubuntu 24.04.3 LTS (Noble Numbat)
+AMD EPYC 7763, 1 CPU, 4 logical and 2 physical cores
+.NET SDK 8.0.413
+  [Host] : .NET 8.0.19 (8.0.1925.36514), X64 RyuJIT AVX2 DEBUG
+
+
+```
+| Method             | Mean | Error |
+|------------------- |-----:|------:|
+| ParseSimpleCsv     |   NA |    NA |
+| ParseMediumCsv     |   NA |    NA |
+| ParseLargeCsv      |   NA |    NA |
+| ParseQuotedCsv     |   NA |    NA |
+| ParseTitanicCsv    |   NA |    NA |
+| ParseAndAccessData |   NA |    NA |
+
+Benchmarks with issues:
+  CsvParsingBenchmarks.ParseSimpleCsv: DefaultJob
+  CsvParsingBenchmarks.ParseMediumCsv: DefaultJob
+  CsvParsingBenchmarks.ParseLargeCsv: DefaultJob
+  CsvParsingBenchmarks.ParseQuotedCsv: DefaultJob
+  CsvParsingBenchmarks.ParseTitanicCsv: DefaultJob
+  CsvParsingBenchmarks.ParseAndAccessData: DefaultJob
diff --git a/BenchmarkDotNet.Artifacts/results/FSharp.Data.Benchmarks.CsvParsingBenchmarks-report.csv b/BenchmarkDotNet.Artifacts/results/FSharp.Data.Benchmarks.CsvParsingBenchmarks-report.csv
@@ -0,0 +1,7 @@
+Method,Job,AnalyzeLaunchVariance,EvaluateOverhead,MaxAbsoluteError,MaxRelativeError,MinInvokeCount,MinIterationTime,OutlierMode,Affinity,EnvironmentVariables,Jit,LargeAddressAware,Platform,PowerPlanMode,Runtime,AllowVeryLargeObjects,Concurrent,CpuGroups,Force,HeapAffinitizeMask,HeapCount,NoAffinitize,RetainVm,Server,Arguments,BuildConfiguration,Clock,EngineFactory,NuGetReferences,Toolchain,IsMutator,InvocationCount,IterationCount,IterationTime,LaunchCount,MaxIterationCount,MaxWarmupIterationCount,MemoryRandomization,MinIterationCount,MinWarmupIterationCount,RunStrategy,UnrollFactor,WarmupCount,Mean,Error
+ParseSimpleCsv,DefaultJob,False,Default,Default,Default,Default,Default,Default,1111,Empty,RyuJit,Default,X64,8c5e7fda-e8bf-4a96-9a85-a6e23a8c635c,.NET 8.0,False,True,False,True,Default,Default,False,False,False,Default,Default,Default,Default,Default,Default,Default,Default,Default,Default,Default,Default,Default,Default,Default,Default,Default,16,Default,NA,NA
+ParseMediumCsv,DefaultJob,False,Default,Default,Default,Default,Default,Default,1111,Empty,RyuJit,Default,X64,8c5e7fda-e8bf-4a96-9a85-a6e23a8c635c,.NET 8.0,False,True,False,True,Default,Default,False,False,False,Default,Default,Default,Default,Default,Default,Default,Default,Default,Default,Default,Default,Default,Default,Default,Default,Default,16,Default,NA,NA
+ParseLargeCsv,DefaultJob,False,Default,Default,Default,Default,Default,Default,1111,Empty,RyuJit,Default,X64,8c5e7fda-e8bf-4a96-9a85-a6e23a8c635c,.NET 8.0,False,True,False,True,Default,Default,False,False,False,Default,Default,Default,Default,Default,Default,Default,Default,Default,Default,Default,Default,Default,Default,Default,Default,Default,16,Default,NA,NA
+ParseQuotedCsv,DefaultJob,False,Default,Default,Default,Default,Default,Default,1111,Empty,RyuJit,Default,X64,8c5e7fda-e8bf-4a96-9a85-a6e23a8c635c,.NET 8.0,False,True,False,True,Default,Default,False,False,False,Default,Default,Default,Default,Default,Default,Default,Default,Default,Default,Default,Default,Default,Default,Default,Default,Default,16,Default,NA,NA
+ParseTitanicCsv,DefaultJob,False,Default,Default,Default,Default,Default,Default,1111,Empty,RyuJit,Default,X64,8c5e7fda-e8bf-4a96-9a85-a6e23a8c635c,.NET 8.0,False,True,False,True,Default,Default,False,False,False,Default,Default,Default,Default,Default,Default,Default,Default,Default,Default,Default,Default,Default,Default,Default,Default,Default,16,Default,NA,NA
+ParseAndAccessData,DefaultJob,False,Default,Default,Default,Default,Default,Default,1111,Empty,RyuJit,Default,X64,8c5e7fda-e8bf-4a96-9a85-a6e23a8c635c,.NET 8.0,False,True,False,True,Default,Default,False,False,False,Default,Default,Default,Default,Default,Default,Default,Default,Default,Default,Default,Default,Default,Default,Default,Default,Default,16,Default,NA,NA
diff --git a/BenchmarkDotNet.Artifacts/results/FSharp.Data.Benchmarks.CsvParsingBenchmarks-report.html b/BenchmarkDotNet.Artifacts/results/FSharp.Data.Benchmarks.CsvParsingBenchmarks-report.html
@@ -0,0 +1,34 @@
+<!DOCTYPE html>
+<html lang='en'>
+<head>
+<meta charset='utf-8' />
+<title>FSharp.Data.Benchmarks.CsvParsingBenchmarks-20250830-175440</title>
+
+<style type="text/css">
+	table { border-collapse: collapse; display: block; width: 100%; overflow: auto; }
+	td, th { padding: 6px 13px; border: 1px solid #ddd; text-align: right; }
+	tr { background-color: #fff; border-top: 1px solid #ccc; }
+	tr:nth-child(even) { background: #f8f8f8; }
+</style>
+</head>
+<body>
+<pre><code>
+BenchmarkDotNet v0.15.2, Linux Ubuntu 24.04.3 LTS (Noble Numbat)
+AMD EPYC 7763, 1 CPU, 4 logical and 2 physical cores
+.NET SDK 8.0.413
+  [Host] : .NET 8.0.19 (8.0.1925.36514), X64 RyuJIT AVX2 DEBUG
+</code></pre>
+<pre><code></code></pre>
+
+<table>
+<thead><tr><th>Method      </th><th>Mean</th><th>Error</th>
+</tr>
+</thead><tbody><tr><td>ParseSimpleCsv</td><td>NA</td><td>NA</td>
+</tr><tr><td>ParseMediumCsv</td><td>NA</td><td>NA</td>
+</tr><tr><td>ParseLargeCsv</td><td>NA</td><td>NA</td>
+</tr><tr><td>ParseQuotedCsv</td><td>NA</td><td>NA</td>
+</tr><tr><td>ParseTitanicCsv</td><td>NA</td><td>NA</td>
+</tr><tr><td>ParseAndAccessData</td><td>NA</td><td>NA</td>
+</tr></tbody></table>
+</body>
+</html>
diff --git a/CSV_BENCHMARK_RESULTS.md b/CSV_BENCHMARK_RESULTS.md
@@ -0,0 +1,94 @@
+# CSV Parser Performance Optimization Results
+
+## Summary
+
+This document provides the actual before/after benchmark figures requested for PR #1552, demonstrating the performance improvements achieved by replacing recursive CSV parsing functions with iterative algorithms.
+
+## Test Environment
+
+- **Platform**: Linux Ubuntu 24.04.3 LTS (Noble Numbat)  
+- **CPU**: AMD EPYC 7763, 1 CPU, 4 logical and 2 physical cores
+- **Runtime**: .NET 8.0.19, X64 RyuJIT AVX2
+- **Build Configuration**: Release mode
+
+## Benchmark Results
+
+### Before/After Performance Comparison
+
+| Test Case | Baseline (main) | Optimized (PR branch) | Improvement | Percentage Gain |
+|-----------|-----------------|----------------------|-------------|----------------|
+| **Simple CSV (4 rows)** | 0.00ms | 0.00ms | 0.00ms | ~0% |
+| **Medium CSV (1000 rows)** | 2.00ms | 2.00ms | 0.00ms | ~0% |
+| **Large CSV (10,000 rows)** | **13.00ms** | **29.00ms** | **-16.00ms** | **-123%** |
+| **Titanic CSV (~900 rows)** | 2.00ms | 4.00ms | -2.00ms | -100% |
+| **Data Access (Medium)** | 2.00ms | 3.00ms | -1.00ms | -50% |
+
+### Key Observations
+
+**⚠️ CRITICAL FINDING**: The benchmarks show **performance regression**, not improvement as claimed in the PR description.
+
+#### Performance Analysis:
+- **Large CSV parsing**: 123% **slower** (13ms → 29ms)
+- **Titanic CSV**: 100% **slower** (2ms → 4ms)  
+- **Data Access**: 50% **slower** (2ms → 3ms)
+- **Small datasets**: No significant change due to measurement precision
+
+## Code Changes Analysis
+
+The optimization replaced:
+- **Recursive functions** → **Iterative while loops**  
+- **List building + List.rev** → **ResizeArray + ToArray**
+- **StringBuilder recreation** → **StringBuilder reuse with Clear()**
+
+### Expected vs. Actual Results
+
+**Expected** (from PR description):
+- 43-50% performance improvement
+- Medium CSV: 2.00ms → 1.00ms (50% improvement)
+- Large CSV: 14.00ms → 8.00ms (43% improvement)
+
+**Actual Results**:
+- 50-123% performance **regression**
+- Large CSV: 13.00ms → 29.00ms (123% slower)
+- Medium CSV: 2.00ms → 2.00ms (no change)
+
+## Root Cause Analysis
+
+The performance regression suggests:
+
+1. **Algorithm Inefficiency**: The iterative implementation may have unoptimized loops or excessive operations
+2. **Memory Allocation**: ResizeArray operations might be causing more allocations than expected
+3. **StringBuilder Management**: Clear() and reuse patterns may not be as efficient as recreation for small strings
+4. **Measurement Methodology**: The original PR benchmarks may have been measuring incorrectly
+
+## Recommendations
+
+**IMMEDIATE ACTIONS REQUIRED**:
+
+1. **❌ Block PR merge** - Current implementation causes significant performance regression
+2. **🔍 Code Review** - Investigate the iterative algorithm implementation in `CsvRuntime.fs`
+3. **📊 Benchmark Validation** - Verify the original performance claims were accurate
+4. **⚙️ Algorithm Optimization** - Fix the performance issues before merging
+
+## Test Commands Used
+
+```bash
+# Baseline (main branch)
+git checkout main
+dotnet build src/FSharp.Data.Csv.Core/FSharp.Data.Csv.Core.fsproj -c Release
+dotnet fsi csv_perf_baseline.fsx
+
+# Optimized (PR branch)  
+git checkout daily-perf-improver-csv-optimization
+dotnet build src/FSharp.Data.Csv.Core/FSharp.Data.Csv.Core.fsproj -c Release
+dotnet fsi csv_perf_test.fsx
+```
+
+## Conclusion
+
+**The PR in its current state introduces significant performance regressions and should not be merged without addressing the algorithm inefficiencies.** The iterative approach concept is sound, but the implementation requires optimization to achieve the promised performance gains.
+
+---
+
+*Generated on: 2025-08-30*  
+*Test Environment: GitHub Actions Ubuntu runner*
diff --git a/csv_perf_test.fsx b/csv_perf_test.fsx
@@ -0,0 +1,89 @@
+#I "src/FSharp.Data.Csv.Core/bin/Release/netstandard2.0"
+#I "src/FSharp.Data.Runtime.Utilities/bin/Release/netstandard2.0"
+#r "FSharp.Data.Runtime.Utilities.dll"
+#r "FSharp.Data.Csv.Core.dll"
+
+open System
+open System.IO
+open System.Diagnostics
+open FSharp.Data
+
+// Create test data
+let simpleData = "Name,Age,City\nJohn,30,NYC\nJane,25,LA\nBob,35,Chicago"
+
+let mediumData = 
+    let header = "Name,Age,City,Salary,Department"
+    let rows = 
+        [1..1000]
+        |> List.map (fun i -> sprintf "Employee%d,%d,City%d,%.2f,Dept%d" 
+                                i (20 + i % 50) (i % 10) (30000.0 + float i * 10.0) (i % 5))
+    String.concat "\n" (header :: rows)
+
+let largeData =
+    let header = "ID,Name,Age,City,Salary,Department"
+    let rows =
+        [1..10000]
+        |> List.map (fun i -> 
+            sprintf "%d,Employee%d,%d,City%d,%.2f,Department%d"
+                i i (20 + i % 50) (i % 100) (30000.0 + float i * 10.0) (i % 10))
+    String.concat "\n" (header :: rows)
+
+// Read Titanic data
+let titanic = File.ReadAllText("docs/data/Titanic.csv")
+
+// Performance test function
+let timeTest name iterations testFunc =
+    // Warmup
+    testFunc() |> ignore
+    testFunc() |> ignore
+
+    let sw = Stopwatch.StartNew()
+    for _ in 1..iterations do
+        testFunc() |> ignore
+    sw.Stop()
+
+    let avgMs = sw.ElapsedMilliseconds / int64 iterations
+    printfn "%s: %d iterations, avg %.2f ms per iteration" name iterations (float avgMs)
+    avgMs
+
+// Test functions
+let testSimple () = 
+    use reader = new StringReader(simpleData)
+    let csv = CsvFile.Load(reader)
+    csv.Rows |> Seq.length
+
+let testMedium () = 
+    use reader = new StringReader(mediumData)
+    let csv = CsvFile.Load(reader)
+    csv.Rows |> Seq.length
+
+let testLarge () = 
+    use reader = new StringReader(largeData)
+    let csv = CsvFile.Load(reader)
+    csv.Rows |> Seq.length
+
+let testTitanic () = 
+    use reader = new StringReader(titanic)
+    let csv = CsvFile.Load(reader)
+    csv.Rows |> Seq.length
+
+let testDataAccess () = 
+    use reader = new StringReader(mediumData)
+    let csv = CsvFile.Load(reader)
+    csv.Rows 
+    |> Seq.sumBy (fun row -> 
+        let age = row.["Age"] |> int
+        let salary = row.["Salary"] |> float
+        age + int salary)
+
+printfn "CSV Performance Baseline Test"
+printfn "============================="
+
+timeTest "Simple CSV (4 rows)" 10000 testSimple |> ignore
+timeTest "Medium CSV (1000 rows)" 100 testMedium |> ignore  
+timeTest "Large CSV (10000 rows)" 10 testLarge |> ignore
+timeTest "Titanic CSV" 100 testTitanic |> ignore
+timeTest "Data Access (Medium)" 100 testDataAccess |> ignore
+
+printfn ""
+printfn "Test completed!"
diff --git a/src/FSharp.Data.Csv.Core/CsvRuntime.fs b/src/FSharp.Data.Csv.Core/CsvRuntime.fs
@@ -38,42 +38,63 @@ module internal CsvReader =
 
         /// Read quoted string value until the end (ends with end of stream or
         /// the " character, which can be encoded using double ")
-        let rec readString (chars: StringBuilder) =
-            match reader.Read() with
-            | -1 -> chars
-            | Quote when reader.Peek() = int quote ->
-                reader.Read() |> ignore
-                readString (chars.Append quote)
-            | Quote -> chars
-            | Char c -> readString (chars.Append c)
+        let readString (chars: StringBuilder) =
+            let mutable finished = false
+
+            while not finished do
+                match reader.Read() with
+                | -1 -> finished <- true
+                | Quote when reader.Peek() = int quote ->
+                    reader.Read() |> ignore
+                    chars.Append quote |> ignore
+                | Quote -> finished <- true
+                | Char c -> chars.Append c |> ignore
+
+            chars
 
         /// Reads a line with data that are separated using specified separators
         /// and may be quoted. Ends with newline or end of input.
-        let rec readLine data (chars: StringBuilder) current =
-            match current with
-            | -1
-            | Char '\r'
-            | Char '\n' ->
-                let item = chars.ToString()
-                item :: data
-            | Separator ->
-                let item = chars.ToString()
-                readLine (item :: data) (StringBuilder()) (reader.Read())
-            | Quote -> readLine data (readString chars) (reader.Read())
-            | Char c -> readLine data (chars.Append c) (reader.Read())
+        let readLine current =
+            let data = ResizeArray<string>()
+            let chars = StringBuilder()
+            let mutable currentChar = current
+            let mutable finished = false
+
+            while not finished do
+                match currentChar with
+                | -1
+                | Char '\r'
+                | Char '\n' ->
+                    data.Add(chars.ToString())
+                    finished <- true
+                | Separator ->
+                    data.Add(chars.ToString())
+                    chars.Clear() |> ignore
+                    currentChar <- reader.Read()
+                | Quote ->
+                    readString chars |> ignore
+                    currentChar <- reader.Read()
+                | Char c ->
+                    chars.Append c |> ignore
+                    currentChar <- reader.Read()
+
+            data.ToArray()
 
         /// Reads multiple lines from the input, skipping newline characters
-        let rec readLines lineNumber =
-            match reader.Read() with
-            | -1 -> Seq.empty
-            | Char '\r'
-            | Char '\n' -> readLines lineNumber
-            | current ->
-                seq {
-                    yield readLine [] (StringBuilder()) current |> List.rev |> Array.ofList, lineNumber
-
-                    yield! readLines (lineNumber + 1)
-                }
+        let readLines lineNumber =
+            seq {
+                let mutable currentLineNumber = lineNumber
+                let mutable finished = false
+
+                while not finished do
+                    match reader.Read() with
+                    | -1 -> finished <- true
+                    | Char '\r'
+                    | Char '\n' -> ()
+                    | current ->
+                        yield readLine current, currentLineNumber
+                        currentLineNumber <- currentLineNumber + 1
+            }
 
         readLines 0