yyka created FLINK-39968:
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Summary: [Optimization] Reduce redundant AtomicBoolean allocation
in MemorySegment to improve construction performance
Key: FLINK-39968
URL: https://issues.apache.org/jira/browse/FLINK-39968
Project: Flink
Issue Type: Improvement
Components: API / Core
Reporter: yyka
h2. Background & Problem Analysis
# *{{MemorySegment}} core usage scenarios*
{{MemorySegment}} is the core memory abstraction of Flink, which has two key
usage scenarios:
** {*}Memory buffer pool{*}: Manages reusable memory blocks (network buffers,
managed memory), requiring explicit {{free()}} to reclaim memory;
** {*}In-operator-chain data copy transmission{*}: When the pipeline
configuration {{pipeline.object-reuse = false}} (default off), a large number
of temporary {{MemorySegment}} instances are created for data copy transmission
between operators, and these instances *never call the {{free()}} method*
during their lifecycle.
# *Redundant object allocation overhead*
The current {{MemorySegment}} unconditionally initializes a {{final
AtomicBoolean isFreedAtomic}} in the constructor:
*this.isFreedAtomic = new AtomicBoolean(false);*
In the in-operator-chain data copy transmission (the default scenario with
massive temporary segment creation), {{isFreedAtomic}} is never used, resulting
in meaningless object allocation;
Massive creation of temporary {{AtomicBoolean}} objects increases GC pressure
and constructor execution time, which directly affects the throughput of
high-concurrent streaming jobs.
h2. Optimization Plan
# Replace the member variable {{final AtomicBoolean isFreedAtomic}} with a
primitive {{{}boolean isFreed{}}};
# Add the {{synchronized}} modifier to the {{free()}} method to ensure the
atomicity and thread safety of the free state judgment and modification;
# Retain all original functional logic of the {{free()}} method, only optimize
the underlying state storage and thread safety implementation.
h2. Benchmark Test Results
# {*}Micro-benchmark (new MemorySegment){*}: Using primitive boolean instead
of {{new AtomicBoolean}} reduces constructor overhead, with *3% performance
improvement* for single instance creation;
# {*}End-to-end benchmark (Nexmark){*}: The overall job throughput is
improved, and GC frequency/pause time is reduced, verifying the effectiveness
of the optimization in real streaming scenarios.
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