Degraded performance for serializer retrieval for interred types when using 1.5.0

[Bachemedei]

Description

Retrieval of built-in serializers for inferred types is significantly slower when using Kotlinx-serialization 1.5.0 without the compiler plugin.

We have an operation which reads 1000 events from a database, iterates through the returned rows and deserializes with:

rowList.map { row ->
	val metadata: Map<String, String> = Json.decodeFromString(row.metadata)
	...
}

Below is a heatmap of the duration (ms) for otel traces for the operation described above. Between 10:25AM and 11:15AM we were running kotlinx-serialization 1.5.0 and Kotlin 1.8.0. Prior to, and after that, we were running kotlinx-serialization 1.3.3 and Kotlin 1.8.0. The duration of each operation steadily increased when using kotlinx-serialization 1.5.0.

Example of a span during the timeframe that kotlinx-serialization 1.5.0 was being used:

Benchmarks

Simple benchmarks were written to compare versions of kotlinx-serialization and Kotlin, which can be found here.

The first benchmark was designed to reproduce the issue we were experiencing:

fun retrieveSerializerPerIteration() {  
	repeat(1000) {  
		val metadata: Map<String, String> = Json.decodeFromString(json)  
	}  
}

To verify that the serializer lookup was the cause, a second benchmark was written which retrieved the serializer only once:

fun retrieveSerializerOnce() {  
	val serializer = serializer<Map<String, String>>()  
	repeat(1000) {  
		val metadata: Map<String, String> = Json.decodeFromString(serializer, json)  
	}  
}

Results (Average time per operation):

kotlin-x serialization	kotlin	retrieve serializater per iteration	retrieve serializater once
1.5.0	1.8.0	1868.430 ms/op	1.440 ms/op
1.5.0	1.8.21	1909.756 ms/op	1.383 ms/op
1.3.3	1.8.0	2.513 ms/op	0.483 ms/op
1.3.3	1.8.21	2.594 ms/op	0.493 ms/op

The benchmarks were run again, but with the addition of the serialization compiler plugin:

kotlin-x serialization	kotlin	retrieve serializater per iteration	retrieve serializater once
1.5.0	1.8.0	0.334 ms/op	0.356 ms/op
1.5.0	1.8.21	0.337 ms/op	0.361 ms/op
1.3.3	1.8.0	2.501 ms/op	0.490 ms/op
1.3.3	1.8.21	2.481 ms/op	0.475 ms/op

Expected behavior

Time to retrieve serializers for built in classes should be the same when using kotlinx-serialization 1.5.0/1.3.3 without the compiler plugin.

Environment

• Kotlin version: 1.8.0 & 1.8.21
• Library version: 1.5.0
• Kotlin platforms: JVM
• Gradle version: 8.1
• Postgresql driver version: 42.4.3
• HikariCP version: 5.0.0

[shanshin]

Hi,
this performance degradation relates to #2274, fix will be released in 1.5.1

[Bachemedei]

Benchmarks looking great with 1.5.1, thank you 👍