Serialization optimization for DDB enhanced Client

[RanVaknin]

This PR addresses a performance degradation issue between v1 and v2. After considering multiple implementation approaches, the proposed optimization approach yielded significant reduction in latency across the board.

toJson() Benchmarks

Metrics	p0.90	p0.95	p0.99	Change (p90)
v1	611µs	634µs	739µs	baseline
v2 Current	2,953µs	2,527µs	2,404µs	+383%
**v2 SDKJsonGenerator - writes to byteArrayOutputStream	550µs	564µs	613µs	- 10%
v2 JsonGenerator - writes to stringWriter	680µs	719µs	1541µs	+11%

getJson() Benchmarks

50 bytes payload

Metrics	p0.50	p0.90	p0.99	Change (p90)
v1	0.125µs	0.167µs	0.209µs	baseline
v2 current	0.291µs	0.292µs	0.417µs	+75%
v2 Optimized	0.167µs	0.250µs	0.458µs	+50%

100 bytes payload

Metrics	p0.50	p0.90	p0.99	Change (p90)
v1	0.208µs	0.209µs	0.292µs	baseline
v2 current	0.708µs	0.833µs	1.082µs	+299%
v2 Optimized	0.250µs	0.292µs	0.417µs	+40%

500 bytes payload

Metrics	p0.50	p0.90	p0.99	Change (p90)
v1	0.542µs	0.584µs	0.750µs	baseline
v2 current	2.292µs	2.416µs	3.084µs	+314%
v2 Optimized	0.625µs	0.667µs	0.833µs	+14%

1KB payload

Metrics	p0.50	p0.90	p0.99	Change (p90)
v1	1.250µs	1.374µs	1.708µs	baseline
v2 current	5.040µs	5.456µs	6.792µs	+297%
v2 Optimized	1.332µs	1.416µs	1.792µs	+3%

---

High level Solution

Current Flow:

AttributeValue → JsonNode (via JsonItemAttributeConverter) → String (via JsonStringFormatHelper) → Stream joining

Proposed Flow:

AttributeValue → SDKJsonGenerator → String

General Optimization Approach

Instead of converting each AttributeValue to a JsonNode and then converting JsonNode to string via costly string builder and stream collection , we serialize AttributeValues directly using SDKJsonGenerator methods which delegates all escaping and buffer management to Jackson core.

SdkJsonGenerator (ByteArrayOutputStream) vs JsonGenerator (StringWriter)

Tested both serialization approaches with identical enum dispatch logic:
• SdkJsonGenerator wraps JsonFactory.createGenerator(ByteArrayOutputStream) → creates UTF8JsonGenerator - 19% faster (550µs vs 680µs at p90)
• JsonGenerator with JsonFactory.createGenerator(StringWriter) → creates WriterBasedJsonGenerator

⚠️ Potential behavior change

UTF8JsonGenerator escapes non ASCII as \uXXXX by default. Jackson 2.18+ provides COMBINE_UNICODE_SURROGATES_IN_UTF8 feature to output literal UTF-8 (verified via test), but the SDK bundles older shaded Jackson version that lacks this feature.
see FasterXML/jackson-core#223
UPDATE this should be mitigated with Jackson 2.19.4 that is now merged.

[dagnir]

BTW can you take this out of draft?

[dagnir]

This PR depends on the COMBINE_UNICODE_SURROGATES_IN_UTF8 feature introduced in Jackson 2.18.0.

We should have a test for this, doesn't look like we have one unless I missed it!

[RanVaknin]

@dagnir do we need a changelog? its an internal implementation - so should be invisible?

[dagnir]

@dagnir do we need a changelog? its an internal implementation - so should be invisible?

Good question; yes we should have an entry for this. It's a significant performance improvement that customers may be interested in.

[sonarqubecloud]

Quality Gate failed

Failed conditions
56.5% Coverage on New Code (required ≥ 80%)
E Reliability Rating on New Code (required ≥ A)

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