F# + Scriban - HTML Template Parsing Benchmarks

I've been experimenting with server-side rendering HTML templates in F# / dotnet as a potential evolution for faster, simpler UIs in CloudSeed - my F# Web API boilerplate. Scriban was a top contender for templating my HTML strings as it's popular in the C# / dotnet community and has a clean, performant API.

As I built UIs with Scriban I noticed that there was an opportunity to cache some templates. But I wasn't sure how impactful this would be and thus whether it would be worth doing.

In this post, we'll explore:

Q: What's the performance difference between Re-Parsing a Template on every call and utilizing a cached Template in Scriban?

Answer

Overall Cached Templates are faster than re-Parsing Templates every time by 5-30%. The difference is more pronounced for smaller templates and becomes less meaningful for larger Templates as Rendering takes up more work. That said, the absolute time differences are incredibly small (< 1 ms) so both approaches will likely scale well (and often much better than other popular approaches like insert-favorite-js-framework-here)

10 Items -> Cached faster (30%, 0.05ms)
100 Items -> Cached faster (20%, 0.1ms)
500 Items -> Raw faster (7%, 0.2ms)
800 Items -> Cached faster (4%, 0.2ms)
1000 Items -> FAIL (Reflection limit)

In the rest of this post we'll explore these benchmark results in greater detail:

Benchmark Setup
Detailed Results
Full Benchmark Code

Source Code:

Benchmark Replit
Full Source Code: Available at bottom of post

Benchmark Setup

I wanted to approximate a "real-world" example for utilizing the Scriban library for HTML templating. To that end, I built a simple HTML template that would display data in a table. Each row is a string which we pre-compute before the benchmarks.

Simple Template

// HAMY: A simple html doc
let testTemplate1 = 
    """
    <!DOCTYPE html>
    <html lang="en">
    <head>
        <meta charset="UTF-8">
        <title>Sentinels Example</title>
    </head>
    <body>
        <main>
            <h1>Sentinels Table</h1>  
        </main>
        <table>
            <tr>
                <th>item</th>
            </tr>
            {{ for item in Items }}
                <tr>
                    <td>{{ item }}</td>
                </tr>
            {{ end }}
        </table>
    </body>
    </html>
    """

This allows us to test the full life cycle of a template which is closer to what I cared about for my usage:

Parsing
Rendering - with data population

For this benchmark I wanted to test two versions:

CachedParser - We Parse the template then benchmark rendering with the CachedParser
RawParser - We Parse and Render the template every time we call it.

let cachedParser 
    (template : string)
    = 
    let compiledTemplate = Scriban.Template.Parse(template)

    fun (props : TemplateProps) ->
        compiledTemplate.Render(
            props,
            memberRenamer = fun m -> m.Name)

let rawParser 
    (template : string) 
    (props : TemplateProps) 
    =
    let compiledTemplate = Scriban.Template.Parse(template)
    compiledTemplate.Render(
        props,
        memberRenamer = fun m -> m.Name)

let cachedParserTest1 = cachedParser testTemplate1

let rawParserTest1 = rawParser testTemplate1

For Benchmarking, I utilized BenchmarkDotNet - a popular, battle-hardened framework for running benchmarks w dotnet.

Detailed Results

I ran the Benchmark multiple times with varying data sizes to get a better idea of how the library performed under different circumstances (larger and smaller HTML templates).

Terms:

ms = millisecond (0.001 seconds)
us = microsecond (0.000001 seconds)

Scriban Benchmark - 10 Items

10 Items

Overall: Cached faster (30%, 0.05ms)

CachedParser:

Mean: 0.125 ms
Error: 0.009 ms
StdDev: 0.025 ms

RawParser:

Mean: 0.179 ms
Error: 0.012 ms
StdDev: 0.036 ms

CachedParser is significantly faster but the absolute difference is about 0.05ms which is essentially unnoticeable. For small templates, Scriban is quite fast.

Scriban Benchmark - 100 Items

100 Items

Overall: Cached faster (20%, 0.1ms)

CachedParser:

Mean: 0.430 ms
Error: 0.038 ms
StdDev: 0.108 ms

RawParser:

Mean: 0.518 ms
Error: 0.032 ms
StdDev: 0.094 ms

Here Cached still has an edge of ab 20% but at 0.1ms it's still essentially unnoticeable. Interestingly it seems that the work is scaling sublinearly - we required 10 times more data population but only needed ~4x more time to do so.

Scriban Benchmark - 500 Items

500 Items

Overall: Raw faster (7%, 0.2ms)

CachedParser:

Mean: 3.039 ms
Error: 0.175 ms
StdDev: 0.501 ms

RawParser:

Mean: 2.816 ms
Error: 0.194 ms
StdDev: 0.565 ms

Here we start to push Scriban a bit. It's unlikely that you'll want to actually render 500 items in a list like this but I think this starts to show us what it's like if we have a more complex template populating lots of different data totaling a few hundred fields. Still Scriban handles it quite well with a mean of 3 ms (unnoticeable to a human though perhaps noticeable to our systems) and with the raw / cached parsers just 0.2 ms different.

Scriban Benchmark - 800 Items

800 Items

Overall: Cached faster (4%, 0.2ms)

CachedParser:

Mean: 5.112 ms
Error: 0.186 ms
StdDev: 0.541 ms

RawParser:

Mean: 5.321 ms
Error: 0.303 ms
StdDev: 0.882 ms

Here we reach the extremes of what Scriban is built for (seriously, at 1000 items we broke it). Yet it still performs remarkably well with ~5 ms renders for a truly unreasonable amount of data being displayed on screen. Even at this juncture, the difference between raw and cached parsing remains small (~0.2 ms) giving me confidence that both are generally fine approaches with little / no performance difference between them.

Scriban Benchmark - 1000 Items

1000 Items

Overall: Failed

Here we seem to push Scriban to its limits. It seems we get blocked by a System.Reflection.TargetInvocationException presumably for doing too many iterations as part of this process. My guess is this limit is here because Reflection is generally slow / expensive and it wants to prevent you from crashing yourself accidentally. My other guess is that we could probably lift this limit with some configuration but I think 1000 items is mostly unnecessary for UI renders and thus it's okay this breaks for our purposes.

Full Benchmark Code

Here's a dump of the benchmark code as used to get these results. You can also run this benchmark on Replit.

open BenchmarkDotNet.Attributes
open BenchmarkDotNet.Running
open Scriban
open System

(*
* ToRun: dotnet run -c Release
*)

type TemplateProps = 
    {
        Items : string list
    }

type ScribanBenchmarks() =

    let itemCount = 800

    let testItems = 
        seq {0 .. itemCount}
        |> Seq.map 
            (fun _ -> Guid.NewGuid().ToString())
        |> Seq.toList
  
    // HAMY: A simple html doc
    let testTemplate1 = 
        """
        <!DOCTYPE html>
        <html lang="en">
        <head>
            <meta charset="UTF-8">
            <title>Sentinels Example</title>
        </head>
        <body>
            <main>
                <h1>Sentinels Table</h1>  
            </main>
            <table>
                <tr>
                    <th>item</th>
                </tr>
                {{ for item in Items }}
                    <tr>
                        <td>{{ item }}</td>
                    </tr>
                {{ end }}
            </table>
        </body>
        </html>
        """
  
    let cachedParser 
        (template : string)
        = 
        let compiledTemplate = Scriban.Template.Parse(template)
    
        fun (props : TemplateProps) ->
            compiledTemplate.Render(
              props,
              // HAMY: Overload memberRenamer so var names are the same
              // Source: https://github.com/scriban/scriban/blob/master/doc/runtime.md#member-renamer
              memberRenamer = fun m -> m.Name)
  
    let rawParser 
        (template : string) 
        (props : TemplateProps) 
        =
        let compiledTemplate = Scriban.Template.Parse(template)
        compiledTemplate.Render(
          props,
          // HAMY: Overload memberRenamer so var names are the same
          // Source: https://github.com/scriban/scriban/blob/master/doc/runtime.md#member-renamer
          memberRenamer = fun m -> m.Name)

    let cachedParserTest1 = cachedParser testTemplate1

    let rawParserTest1 = rawParser testTemplate1

    [<Benchmark>]
    member __.RunCachedParser() = 
        cachedParserTest1 { Items = testItems }

    [<Benchmark>]
    member __.RunRawParser() =  
        rawParserTest1 { Items = testItems }

[<EntryPoint>]
let main argv =
    printfn "Hello World from F#!"

    let summary = BenchmarkRunner.Run<ScribanBenchmarks>();
    
    0 // return an integer exit code

I'm pleasantly surprised with how easy / performant HTML template parsing has been in F# / dotnet. I'll likely continue experimenting and try using it for more of my projects.

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F# + Scriban - HTML Template Parsing Benchmarks

Answer

Benchmark Setup

Detailed Results

Full Benchmark Code

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