Really poor performance with streaming parser

[bryanmatteson]

Really poor performance with streaming parser

[ahives]

Can you please add your query.

[bryanmatteson]

The issue is actually separate from any query. The problem is in parser.ParseStream. Here's a full main function that can reproduce the issue with the file I attached.

private static async Task Main(string[] args) {
    var filePath = "HR7Message.txt";

    ISchema<HL7V26Entity> schema = Schema.Factory.CreateHL7<HL7V26Entity>(cfg => cfg.AddFromNamespaceContaining<HL7Version26>());
    IEntityParser<HL7V26Entity> parser = Parser.Factory.CreateHL7(schema);

    using var stream = File.OpenRead(filePath);
    StreamText text = await new StreamTextReader(stream).Text;
    var parse = await parser.ParseStream(text, new TextSpan(0, text.Length)); // <-- problem is here
}

[dominiqueplante]

Hi @bryanmatteson

I created a branch with your message and added a performance benchmark

See this branch

I am running 2.2 Ghz I7 2016 MacBookPro and here are the performance benchmarks I got

// * Detailed results *
StreamingParserBenchmarks.StreamingParserBenchmark: Job-KKEHVM(Runtime=Core, InvocationCount=5, LaunchCount=1, RunStrategy=Throughput, TargetCount=5, UnrollFactor=1, WarmupCount=5)
Runtime = .NET Core 2.1.13 (CoreCLR 4.6.28008.01, CoreFX 4.6.28008.01), 64bit RyuJIT; GC = Concurrent Workstation
Mean = 284.0624 ms, StdErr = 0.6272 ms (0.22%); N = 5, StdDev = 1.4024 ms
Min = 282.4000 ms, Q1 = 282.9314 ms, Median = 284.0312 ms, Q3 = 285.2089 ms, Max = 286.2371 ms
IQR = 2.2775 ms, LowerFence = 279.5152 ms, UpperFence = 288.6251 ms
ConfidenceInterval = [278.6631 ms; 289.4617 ms] (CI 99.9%), Margin = 5.3993 ms (1.90% of Mean)
Skewness = 0.4, Kurtosis = 1.56, MValue = 2
-------------------- Histogram --------------------
[281.682 ms ; 286.955 ms) | @@@@@
---------------------------------------------------

Total time: 00:00:26 (26.77 sec)

// * Summary *

BenchmarkDotNet=v0.10.14, OS=macOS 10.14.2 (18C54) [Darwin 18.2.0]
Intel Core i7-4770HQ CPU 2.20GHz (Haswell), 1 CPU, 8 logical and 4 physical cores
.NET Core SDK=3.1.201
  [Host]     : .NET Core 2.1.13 (CoreCLR 4.6.28008.01, CoreFX 4.6.28008.01), 64bit RyuJIT
  Job-KKEHVM : .NET Core 2.1.13 (CoreCLR 4.6.28008.01, CoreFX 4.6.28008.01), 64bit RyuJIT

Runtime=Core  InvocationCount=5  LaunchCount=1  
RunStrategy=Throughput  TargetCount=5  UnrollFactor=1  
WarmupCount=5  

                   Method |     Mean |    Error |   StdDev |      Min |      Max |     Gen 0 |    Gen 1 |    Gen 2 | Allocated |
------------------------- |---------:|---------:|---------:|---------:|---------:|----------:|---------:|---------:|----------:|
 StreamingParserBenchmark | 284.1 ms | 5.399 ms | 1.402 ms | 282.4 ms | 286.2 ms | 1200.0000 | 800.0000 | 400.0000 |  15.46 MB |

// * Legends *
  Mean      : Arithmetic mean of all measurements
  Error     : Half of 99.9% confidence interval
  StdDev    : Standard deviation of all measurements
  Min       : Minimum
  Max       : Maximum
  Gen 0     : GC Generation 0 collects per 1k Operations
  Gen 1     : GC Generation 1 collects per 1k Operations
  Gen 2     : GC Generation 2 collects per 1k Operations
  Allocated : Allocated memory per single operation (managed only, inclusive, 1KB = 1024B)
  1 ms      : 1 Millisecond (0.001 sec)

// * Diagnostic Output - MemoryDiagnoser *


// ***** BenchmarkRunner: End *****
// * Artifacts cleanup *

[bryanmatteson]

Right, this is the workaround. In your benchmark, you load the entire stream into memory first, and then use a StringReader and finally a TextReaderStreamTextReader. This will work because it never needs to load another chunk from the stream as it has already been loaded completely into memory by your call to File.ReadAllText(_largeFilePath).

If you change the benchmark to use the StreamTextReader directly, like this:

[Benchmark]
public async Task StreamingParserBenchmarkLargeFileDemo() {
    Console.WriteLine("Starting streaming parser benchmark run");

    using (var stream = File.OpenRead(_largeFilePath)) {
        //Console.WriteLine("About to parse stream");
        StreamText text = await new StreamTextReader(stream).Text;
        ParseResult<HL7Entity> result = await _hl7Parser.ParseStream(text, new TextSpan(0, text.Length));
        ...

then I think you'll run into the bug I'm seeing. So while not using the StreamTextReader is a potential solution, there still exists a bug in the stream parsing logic for really long lines.