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https://issues.apache.org/jira/browse/SPARK-59802?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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ASF GitHub Bot updated SPARK-59802:
-----------------------------------
Labels: pull-request-available (was: )
> Multiply compact decimals without allocating BigDecimal
> -------------------------------------------------------
>
> Key: SPARK-59802
> URL: https://issues.apache.org/jira/browse/SPARK-59802
> Project: Spark
> Issue Type: Improvement
> Components: SQL
> Affects Versions: 4.1.0
> Reporter: David Mollitor
> Priority: Minor
> Labels: pull-request-available
>
> h3. What
> {{Decimal}} keeps small values in a compact {{long}} ({{decimalVal == null}})
> and only expands to a {{java.math.BigDecimal}} beyond 18 digits, but
> {{Decimal.*}} always went through {{toJavaBigDecimal.multiply(...,
> MATH_CONTEXT)}} with no compact path -- a row-level {{a * b}} on two compact
> operands allocated two operand {{BigDecimal}}s, a result {{BigDecimal}}, and
> its {{BigInteger}}.
> Add a compact {{long}} fast path for {{*}}, mirroring the existing same-scale
> {{+}}/{{-}}: when both operands are compact and the exact product fits the
> 18-digit compact range (overflow-checked via {{Math.multiplyHigh}}), multiply
> the unscaled longs directly; otherwise fall back to the existing BigDecimal
> path.
> h3. Why
> Avoids per-row {{BigDecimal}}/{{BigInteger}} allocation for the common
> small-decimal case (e.g. multiplying {{decimal(7,2)}} prices/amounts). On a
> full TPC-DS v1.4 (SF10) JFR run, {{BigDecimal}} allocations attributed to
> {{Decimal.*}} dropped ~93%. Correctness-neutral (byte-identical): the fast
> path runs only where no rounding occurs, and high-precision operands
> (including the SPARK-45786 case) keep the BigDecimal path; {{CheckOverflow}}
> re-normalizes precision/scale exactly as before.
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