Cleanup OutputBufferMemoryManager and peak memory calculations

[pettyjamesm]

Description

OutputBufferMemoryManager

• Switch the relatively more expensive AtomicLong#updateAndGet for AtomicLong#accumulateAndGet operation
• Check currentBufferedBytes > bufferedBytes.get() before calling bufferedBytes.accumulateAndGet(currentBufferedBytes, Math::max) since a volatile read is cheaper than a volatile write and updating the maximum is not the common case.
• Refactor getUtilization logic to avoid unnecessary volatile reads
• Make the class final

Peak Memory Calculations

• Updates various places where peak memory is calculated using AtomicLong to check whether the value is greater than peak before calling into AtomicLong::accumulateAndGet so to avoid unnecessary contention on volatile updates

Release notes

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Summary by Sourcery

Improve performance and simplify synchronization in OutputBufferMemoryManager by replacing atomic operations, reducing volatile writes, refactoring utilization tracking, and marking the class as final

Bug Fixes:

• Introduce an IllegalStateException on negative buffer adjustments instead of using updateAndGet’s argument check

Enhancements:

• Replace AtomicLong#updateAndGet with AtomicLong#addAndGet and explicit negative-value check to reduce overhead
• Guard peakMemoryUsage updates behind a conditional volatile read to avoid unnecessary writes
• Refactor getUtilization and recordBufferUtilization to accept the currentBufferedBytes parameter and eliminate redundant volatile reads
• Mark OutputBufferMemoryManager as a final class to prevent subclassing

[sourcery-ai]

Reviewer's Guide

This PR refactors OutputBufferMemoryManager to improve performance by replacing expensive atomic operations with cheaper alternatives, reducing volatile writes for peak memory tracking, streamlining utilization recording logic, and enforcing immutability by making the class final.

Class diagram for refactored OutputBufferMemoryManager

classDiagram
    class OutputBufferMemoryManager {
        -AtomicLong bufferedBytes
        -AtomicLong peakMemoryUsage
        -long maxBufferedBytes
        -TDigest bufferUtilization
        -long lastBufferUtilizationRecordTime
        -double lastBufferUtilization
        -Ticker ticker
        -ListenableFuture<Void> blockedOnMemory
        -ListenableFuture<Void> bufferBlockedFuture
        -MemoryContext memoryContext
        +updateMemoryUsage(long bytesAdded)
        +getBufferedBytes()
        +getUtilization()
        +getUtilizationHistogram()
        -recordBufferUtilization(long currentBufferedBytes)
        -getUtilization(long currentBufferedBytes)
    }
    note for OutputBufferMemoryManager "Class is now final"

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File-Level Changes

Change	Details	Files
Enforce immutability of OutputBufferMemoryManager	Declared class as final	core/trino-main/src/main/java/io/trino/execution/buffer/OutputBufferMemoryManager.java
Replace AtomicLong#updateAndGet with addAndGet and manual overflow check	Switched to bufferedBytes.addAndGet(bytesAdded) Added check for negative result and fallback set with exception on error	core/trino-main/src/main/java/io/trino/execution/buffer/OutputBufferMemoryManager.java
Optimize peakMemoryUsage update to avoid unnecessary volatile writes	Moved accumulateAndGet under a conditional volatile read check Removed unconditional peakMemoryUsage update	core/trino-main/src/main/java/io/trino/execution/buffer/OutputBufferMemoryManager.java
Refactor buffer utilization logic to reduce volatile reads	Changed recordBufferUtilization to accept currentBufferedBytes parameter Extracted getUtilization(long) and updated calls to pass bufferedBytes Updated utilization histogram method to record after reading bufferedBytes	core/trino-main/src/main/java/io/trino/execution/buffer/OutputBufferMemoryManager.java

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[sourcery-ai]

Hey there - I've reviewed your changes and they look great!

Prompt for AI Agents

Please address the comments from this code review:

## Individual Comments

### Comment 1
<location> `core/trino-main/src/main/java/io/trino/execution/buffer/OutputBufferMemoryManager.java:102-105` </location>
<code_context>
-                checkArgument(result >= 0, "bufferedBytes (%s) plus delta (%s) would be negative", bytes, bytesAdded);
-                return result;
-            });
+            currentBufferedBytes = bufferedBytes.addAndGet(bytesAdded);
+            if (currentBufferedBytes < 0) {
+                bufferedBytes.set(currentBufferedBytes - bytesAdded);
+                throw new IllegalStateException("bufferedBytes (%s) plus delta (%s) is negative".formatted(bufferedBytes.get(), bytesAdded));
+            }
             ListenableFuture<Void> blockedOnMemory = memoryContext.setBytes(currentBufferedBytes);
</code_context>

<issue_to_address>
**issue (bug_risk):** Switching from updateAndGet with checkArgument to addAndGet with post-check changes error handling.

This method allows bufferedBytes to be negative briefly, which may be visible to other threads. Evaluate if this could lead to issues, or consider using a compare-and-set loop for stricter consistency.
</issue_to_address>

### Comment 2
<location> `core/trino-main/src/main/java/io/trino/execution/buffer/OutputBufferMemoryManager.java:127-128` </location>
<code_context>
+            recordBufferUtilization(currentBufferedBytes);
+        }
+        // Reduce contention by reading first and only updating if the new value might become the maximum (uncommon)
+        if (currentBufferedBytes > peakMemoryUsage.get()) {
+            peakMemoryUsage.accumulateAndGet(currentBufferedBytes, Math::max);
         }
-        peakMemoryUsage.accumulateAndGet(currentBufferedBytes, Math::max);
</code_context>

<issue_to_address>
**issue (bug_risk):** Optimizing peakMemoryUsage update reduces contention but may miss some updates.

This approach can miss updates to peakMemoryUsage due to race conditions between threads. Assess if this potential inaccuracy aligns with your application's requirements.
</issue_to_address>

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