v0.14.2 introduced significant performance degradation

We use Circe in several Scala cron jobs. Last week or so, we upgraded Circe from v0.14.1 to v0.14.2, and some cron jobs took several times longer to complete.

We ran some profiling and found that https://github.com/circe/circe/pull/1617/ caused this performance reduction by introducing a new cursorToDecodingFailure function in modules/core/shared/src/main/scala/io/circe/Decoder.scala that takes linear time to run.

Example

Demo.sc

import io.circe.Codec
import io.circe.generic.extras.Configuration
import io.circe.generic.extras.semiauto.deriveConfiguredCodec
import io.circe.parser.decode

import java.util.UUID
import scala.io.Source

case class Cat(
    id: UUID,
    friends: Seq[Cat] = Seq.empty
)

object Cat {
  implicit final val configuration: Configuration = Configuration.default.withDefaults
  implicit val personDecoder: Codec[Cat] = deriveConfiguredCodec
}

case class Dog(
    id: UUID,
    friends: Option[Seq[Dog]] = None
)

object Dog {
  implicit final val configuration: Configuration = Configuration.default.withDefaults
  implicit val personDecoder: Codec[Dog] = deriveConfiguredCodec
}

val fileSource = Source.fromFile("uuid-10k.json")
val fileContent = fileSource.getLines.mkString
fileSource.close()

val catStartTime = java.lang.System.currentTimeMillis()
decode[Seq[Cat]](fileContent)
println(s"Time taken for cats: ${java.lang.System.currentTimeMillis() - catStartTime} ms")

val dogStartTime = java.lang.System.currentTimeMillis()
decode[Seq[Dog]](fileContent)
println(s"Time taken for dogs: ${java.lang.System.currentTimeMillis() - dogStartTime} ms")

uuid-10k.json

[{"id":"19b10dec-91fe-42ee-8da7-2cafe9529dad"},{"id":"2da8de7d-02fe-479c-8293-4bebbd24c4ef"}, ... ]

Result

Time taken for cats: 3758 ms
Time taken for dogs: 154 ms

Cats and Dogs are pretty similar. Surprisingly, one is significantly slower than the other. I believe many people use the style in the case class Cat to represent potentially empty list fields. This will cause problems in some production environments once they switch to v0.14.2.

[sbuzzard]

yep, fixed my issue as well., thx.

[zarthross]

👍 Thanks for re-running that. We have some PRs in progress to hopefully help with that. See https://github.com/circe/circe/pull/1974