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This is a work-in-progress. I'm trying to make a DiagnosticSource listener that writes to InfluxDB with minimal overhead, using the new Span/Memory APIs. The default InfluxDB C# client is very allocate-y, creating lots of Dictionary<string,object> and Dictionary<string,string> instances and other things for every write. This library instead writes directly from the objects passed to DiagnosticSource.Write to a managed buffer of UTF8 bytes, and sends the buffers to InfluxDB when they get full.


It's tricky to benchmark this, because sending the data to InfluxDB involves a lot of async background batching stuff, but I've created a BenchmarkDotNet project (in the perf directory) to compare the conversion of objects to InfluxDB format. The official client exposes a PointData type which takes two IReadOnlyDictionary instances, and then actually converts those to new Dictionary instances in the constructor. So the benchmark compares constructing PointData instances to using the InfluxLineFormatter to write directly to a Span<byte>.

The benchmark code writes 128

Results from the benchmark:

LineFormatter is this project. PointData is the official client, run with 128 items and 1024 items for each.

BenchmarkDotNet=v0.11.0, OS=Windows 10.0.17134.165 (1803/April2018Update/Redstone4)
Intel Core i7-4770K CPU 3.50GHz (Haswell), 1 CPU, 8 logical and 4 physical cores
.NET Core SDK=2.1.302
  [Host]     : .NET Core 2.1.2 (CoreCLR 4.6.26628.05, CoreFX 4.6.26629.01), 64bit RyuJIT
  DefaultJob : .NET Core 2.1.2 (CoreCLR 4.6.26628.05, CoreFX 4.6.26629.01), 64bit RyuJIT

Method Mean Error StdDev Median Gen 0 Gen 1 Allocated
LineFormatter128 60.76 us 0.4592 us 0.4295 us 60.69 us 5.0049 - 20.52 KB
PointData128 128.14 us 1.4037 us 1.3130 us 127.47 us 34.4238 0.9766 141.02 KB
LineFormatter1024 493.18 us 4.7369 us 4.1991 us 493.09 us 39.0625 - 163.98 KB
PointData1024 1,204.12 us 25.6625 us 48.8256 us 1,181.42 us 183.5938 91.7969 1128.02 KB

LineFormatter is significantly faster, with more than double the throughput, and only 15% of the memory usage and allocations. I'm not quite sure where those allocations are happening, tbh, because once the Formatter is created, it should be allocation free from then on. I'm doing some profiling to try and track those down.

Also notice with the PointData code with 1024 items, we start to get a lot of objects moving to Gen 1, which we should try to avoid in hot-path code. All of LineFormatter's heap-allocated objects are created for the lifetime of the application, so they should just end up in Gen 2 and not get in anybody's way.

(Aside: why isn't there a separate heap for objects that will never be collected until the process exits?)

Additional notes

In the official client, once these PointData instances have been constructed, they get buffered for however long the batch interval is, and then used to create a System.Net.Http.StringContent via a process which involves creating a lot of intermediate strings. That all happens on top of the benchmarked code above.

This project is using pooled byte[] arrays and writing directly to them from the instrumentation code, so once a buffer is full or the batch interval is hit, that array is just wrapped in a System.Net.Http.ByteArrayContent and posted; no further processing or allocations are necessary. As noted before, it's hard to benchmark that effectively, but maybe at some point I'll try to profile it with dotTrace/dotMemory or maybe ANTS in a real application.


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