Optimize InstantDeserializer method replaceZeroOffsetAsZIfNecessary() by schlosna · Pull Request #266 · FasterXML/jackson-modules-java8 (original) (raw)

While reviewing some JFRs from some services that heavily use Jackson for deserializing timestamps, I noticed that com.fasterxml.jackson.datatype.jsr310.deser.InstantDeserializer.replaceZeroOffsetAsZIfNecessary(String) was allocating a lot of int[] from its use of java.util.regex.Pattern.matcher(CharSequence) to determine whether an input String is a zero offset and if so replace it with Z.

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I would like to propose an alternative implementation to avoid expensive regex matcher allocations when replacing zero offset with 'Z'.

Using a JMH benchmark with a variety of generated timestamps I see the following results on x64 (~7x speedup) and aarch64 (~2.5x speedup):

OpenJDK 17.0.6 on x64 Intel(R) Xeon(R) Platinum 8259CL CPU @ 2.50GHz

Benchmark                           Mode  Cnt    Score   Error  Units
InstantDeserializerBenchmark.index  avgt    5   19.543 ± 1.384  ns/op
InstantDeserializerBenchmark.regex  avgt    5  155.081 ± 3.234  ns/op

OpenJDK 17.0.6 on aarch64 Apple M1 Pro

Benchmark                           Mode  Cnt   Score   Error  Units
InstantDeserializerBenchmark.index  avgt    5  16.855 ± 0.537  ns/op
InstantDeserializerBenchmark.regex  avgt    5  58.155 ± 1.444  ns/op