Skip to content

Latest commit

 

History

History

JsonSerializerLargeValuesMemoryAllocations

README.md

Serializing large values with System.Text.Json lead to large memory allocations in LOH

This experiments demonstrates large allocations in LOH from JsonSerializer when serializing large strings or byte arrays. The issue occurs because Utf8JsonWriter buffers an entire value in memory before it can be written out to the output stream.

This issue is discussed in more detail in this blog post and this GitHub issue.

Experiment

The experiment is a simple API with 3 endpoints that return JSON payloads with a single Data field.

  • The /string endpoint returns a large string value (the source string contains 1,000,000 characters)
  • The /escaped-string endpoint returns a large string value that contains characters that will require escaping
  • The /binary endpoint returns a large base-64 string encoded from a source byte array with 1,000,000 bytes

The experiment consists of making 1,000 concurrent requests from 50 connections using bombardier while using Visual Studio's .NET Object Allocation Tracking profiler to monitor heap allocations.

Large byte arrays to base-64 encoding

.\bombardier.exe -l -n 1000 -c 50 http://localhost:5174/binary
Bombarding http://localhost:5174/binary with 1000 request(s) using 50 connection(s)
 1000 / 1000 [=======================================================================================] 100.00% 807/s 1s
Done!
Statistics        Avg      Stdev        Max
  Reqs/sec       895.44     407.18    2279.08
  Latency       56.62ms    29.88ms   209.70ms
  Latency Distribution
     50%    41.95ms
     75%    61.32ms
     90%    88.42ms
     95%   182.32ms
     99%   206.17ms
  HTTP codes:
    1xx - 0, 2xx - 1000, 3xx - 0, 4xx - 0, 5xx - 0
    others - 0
  Throughput:     1.07GB/s

alt text

Large string with no escaped characters

.\bombardier.exe -l -n 1000 -c 50 http://localhost:5174/string
Bombarding http://localhost:5174/string with 1000 request(s) using 50 connection(s)
 1000 / 1000 [======================================================================================] 100.00% 1380/s 0s
Done!
Statistics        Avg      Stdev        Max
  Reqs/sec      2066.66    1692.96    6846.19
  Latency       30.68ms    15.60ms   202.43ms
  Latency Distribution
     50%    22.20ms
     75%    25.28ms
     90%    61.26ms
     95%    89.86ms
     99%   143.50ms
  HTTP codes:
    1xx - 0, 2xx - 1000, 3xx - 0, 4xx - 0, 5xx - 0
    others - 0
  Throughput:     1.49GB/s

alt text

Large string with escaped characters

.\bombardier.exe -l -n 1000 -c 50 http://localhost:5174/escaped-string
Bombarding http://localhost:5174/escaped-string with 1000 request(s) using 50 connection(s)
 1000 / 1000 [=======================================================================================] 100.00% 253/s 3s
Done!
Statistics        Avg      Stdev        Max
  Reqs/sec       275.26     255.74    1654.64
  Latency      184.30ms    68.00ms   466.25ms
  Latency Distribution
     50%   168.10ms
     75%   207.65ms
     90%   270.62ms
     95%   368.58ms
     99%   429.57ms
  HTTP codes:
    1xx - 0, 2xx - 1000, 3xx - 0, 4xx - 0, 5xx - 0
    others - 0
  Throughput:     1.08GB/s

alt text

alt text