RFR: 8327791: Optimization for new BigDecimal(String) [v18]

[Chen Liang]

On Sat, 27 Apr 2024 10:48:38 GMT, Shaojin Wen <duke at openjdk.org> wrote:

>> Shaojin Wen has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains 22 additional commits since the last revision:
>> 
>>  - Merge remote-tracking branch 'upstream/master' into optim_dec_new
>>  - Merge remote-tracking branch 'upstream/master' into optim_dec_new
>>  - use while instead for
>>  - Update src/java.base/share/classes/java/math/BigDecimal.java
>>    
>>    Co-authored-by: Claes Redestad <claes.redestad at oracle.com>
>>  - bug fix for CharArraySequence#charAt
>>  - bug fix for CharArraySequence
>>  - fix benchmark
>>  - one CharArraySequence
>>  - restore comment
>>  - easier to compare
>>  - ... and 12 more: https://git.openjdk.org/jdk/compare/47953a00...bb620ba3
>
> In money-related scenarios, such as product prices, etc., BigDecimal needs to be used instead of float/double. I focus on optimizing the performance of BigDecimal's construction and toString scenarios.
> 
> Constructing BigDecimal usually includes two scenarios:
> * new BigDecimal(char[], int, int), Many libraries, such as mysql drveri/fastjson/jackson and other commonly used libraries use this function to construct BigDecimal
> * new BigDecimal(String), There are also many scenarios, such as data integration scenarios, scenarios where json is read from the message queue and then converted into target database row records, often using new BigDecimal(String)
> 
> I did a performance comparison test on Mac Book M1 Pro. The compared branches are:
> * [baseline](https://github.com/wenshao/jdk/tree/upstream_master_0312) https://github.com/wenshao/jdk/tree/upstream_master_0312
> * bb620ba  [Full](https://webrevs.openjdk.org/?repo=jdk&pr=18177&range=17) - [Incremental](https://webrevs.openjdk.org/?repo=jdk&pr=18177&range=16-17) ([bb620ba3](https://git.openjdk.org/jdk/pull/18177/files/bb620ba39a6f1ce17ff273bac54ebb709beb1667))
> 
> 
> # 1. new BigDecimal(String) benchmark
> Execute the following commands respectively 
> 
> make test TEST="micro:java.math.BigDecimals.testConstructorWithHugeString"
> make test TEST="micro:java.math.BigDecimals.testConstructorWithLargeString"
> make test TEST="micro:java.math.BigDecimals.testConstructorWithSmallString"
> make test TEST="micro:java.math.BigDecimals.testConstructorWithString"
> 
> 
> ## benchmark result
> 
> -Benchmark                                      Mode  Cnt    Score   Error  Units #baseline
> -BigDecimals.testConstructorWithHugeString      avgt   15  112.994 ? 2.342  ns/op
> -BigDecimals.testConstructorWithLargeString     avgt   15  114.016 ? 2.529  ns/op
> -BigDecimals.testConstructorWithSmallString     avgt   15   19.526 ? 0.078  ns/op
> -BigDecimals.testConstructorWithString          avgt   15   68.058 ? 0.836  ns/op
> 
> +Benchmark                                      Mode  Cnt    Score    Error  Units #bb620ba
> +BigDecimals.testConstructorWithHugeString      avgt   15   96.838 ?  8.743  ns/op +16.68%
> +BigDecimals.testConstructorWithLargeString     avgt   15   20.904 ?  0.112  ns/op +445.42%
> +BigDecimals.testConstructorWithSmallString     avgt   15   16.083 ?  0.042  ns/op +21.40%
> +BigDecimals.testConstructorWithString          avgt   15   35.912 ?  0.350  ns/op +85.91%
> 
> 
> It can be seen that there is a significant performance improvement in the new BigDecimal(Str...

@wenshao I think @jddarcy means to share performance improvement in client applications, like in fastjson reading of bigdecimal from JSON, by "interesting workload the change improves".

-------------

PR Comment: https://git.openjdk.org/jdk/pull/18177#issuecomment-2080520496