Reduce memory usage in reader by reset all underlying readers #24912

chenyangfb · 2025-04-14T14:49:08Z

Description

Currently for reader with multiple underlying readers (e.g. dictionaryReader and directReader in LongSelectiveStreamReader), only the current reader get reset in startStripe(), the other reader won't get reset, leads to extra memory usage and OOM.

This PR avoid those extra memory usage by reset all underlying readers in startStripe(). This behavior is controlled by resetAllReaders in OrcReaderOptions, and it's disabled by default

Impact

Reduce memory usage in reader.

Test Plan

Tested with Spark workload.
Around 10% workload triggered the code path which reset all underlying readers, leading to less memory usage and OOM.

== RELEASE NOTES ==
General change
* Improve memory usage in reader with nested readers by resetting all nested readers.

sdruzkin · 2025-04-20T02:40:25Z

Please add unit tests checking various combinations of stripe encodings.

sdruzkin · 2025-04-20T02:36:27Z

presto-orc/src/main/java/com/facebook/presto/orc/reader/BatchStreamReaders.java

@@ -40,7 +40,7 @@ public static BatchStreamReader createStreamReader(Type type, StreamDescriptor s
            case INT:
            case LONG:
            case DATE:
-                return new LongBatchStreamReader(type, streamDescriptor, systemMemoryContext);
+                return new LongBatchStreamReader(type, streamDescriptor, systemMemoryContext, options.isResetAllReaders());


Why are you changing batch readers? They are not used in Spark.

Right, those are not used in spark. but I think not reset all underlying readers is a generic bug, hence including them. Let me know if you prefer to keep the current behavior in this PR.

Batch reader is rarely used in prod. I'd suggest to not touch it.

sdruzkin · 2025-04-20T02:37:02Z

presto-orc/src/main/java/com/facebook/presto/orc/reader/LongSelectiveStreamReader.java

@@ -52,9 +52,10 @@ public LongSelectiveStreamReader(
            Optional<Type> outputType,
            OrcAggregatedMemoryContext systemMemoryContext,
            boolean isLowMemory,
-            long maxSliceSize)
+            long maxSliceSize,
+            boolean resetAllReaders)


Don't introduce resetAllReaders, it does not make much sense.

The main purpose of resetAllReaders for performance comparison in prod.
I plan to remove this option if we decide to enable it by default later.
Let me know if this make sense

Please remove it now to make it a default behavior.

sdruzkin · 2025-04-20T02:38:36Z

presto-orc/src/main/java/com/facebook/presto/orc/reader/LongSelectiveStreamReader.java

@@ -73,12 +74,20 @@ public void startStripe(Stripe stripe)
                    directReader = new LongDirectSelectiveStreamReader(context);
                }
                currentReader = directReader;
+                if (dictionaryReader != null && context.isResetAllReaders()) {


I think it would be better to close and nullify the other reader if it exists. Reader creation is not very expensive, and usually stripes stick with the same encoding.

sure. will try that and run some test.

sdruzkin

Overall LGTM. Asks are to 1) remove the new flag and make it default behavior; 2) remove setting system properties.

sdruzkin · 2025-04-24T23:04:33Z

presto-orc/src/main/java/com/facebook/presto/orc/reader/BatchStreamReaders.java

@@ -40,7 +40,7 @@ public static BatchStreamReader createStreamReader(Type type, StreamDescriptor s
            case INT:
            case LONG:
            case DATE:
-                return new LongBatchStreamReader(type, streamDescriptor, systemMemoryContext);
+                return new LongBatchStreamReader(type, streamDescriptor, systemMemoryContext, options.isResetAllReaders());


Batch reader is rarely used in prod. I'd suggest to not touch it.

sdruzkin · 2025-04-24T23:05:26Z

presto-orc/src/main/java/com/facebook/presto/orc/reader/LongSelectiveStreamReader.java

@@ -52,9 +52,10 @@ public LongSelectiveStreamReader(
            Optional<Type> outputType,
            OrcAggregatedMemoryContext systemMemoryContext,
            boolean isLowMemory,
-            long maxSliceSize)
+            long maxSliceSize,
+            boolean resetAllReaders)


Please remove it now to make it a default behavior.

sdruzkin · 2025-04-24T23:05:55Z

presto-orc/src/main/java/com/facebook/presto/orc/reader/LongSelectiveStreamReader.java

                break;
            case DICTIONARY:
                if (dictionaryReader == null) {
                    dictionaryReader = new LongDictionarySelectiveStreamReader(context);
                }
                currentReader = dictionaryReader;
+                if (directReader != null && context.isResetAllReaders()) {
+                    directReader.startStripe(stripe);
+                    System.setProperty("RESET_LONG_READER", "RESET_LONG_READER");


Don't set system properties in OSS, remove this from all classes. If you need it for testing use a build with local changes.

steveburnett · 2025-04-25T14:29:50Z

Thanks for the release note entry! Nits of formatting, so the automation can pick it up for the next release note PR.

== RELEASE NOTES ==

General Changes
* Reduce memory usage in reader with multiple underlying readers by reset all underlying readers.

chenyangfb force-pushed the start_stripe branch from dc0d512 to b09bbaf Compare April 14, 2025 15:24

chenyangfb changed the title ~~Support reset all readers in startStripe()~~ Reduce wasted memory usage in reader by reset all underlying readers Apr 14, 2025

chenyangfb marked this pull request as ready for review April 14, 2025 17:33

chenyangfb requested review from sdruzkin and a team as code owners April 14, 2025 17:33

chenyangfb requested a review from presto-oss April 14, 2025 17:33

chenyangfb changed the title ~~Reduce wasted memory usage in reader by reset all underlying readers~~ Reduce memory usage in reader by reset all underlying readers Apr 14, 2025

chenyangfb force-pushed the start_stripe branch from b09bbaf to c897e09 Compare April 18, 2025 22:03

sdruzkin reviewed Apr 20, 2025

View reviewed changes

sdruzkin reviewed Apr 24, 2025

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Support reset all readers in startStripe()

54a5413

chenyangfb force-pushed the start_stripe branch from c897e09 to 54a5413 Compare May 2, 2025 22:41

sdruzkin approved these changes May 5, 2025

View reviewed changes

sdruzkin merged commit a0562c8 into prestodb:master May 5, 2025
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Reduce memory usage in reader by reset all underlying readers #24912

Reduce memory usage in reader by reset all underlying readers #24912

chenyangfb commented Apr 14, 2025 •

edited by sdruzkin

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sdruzkin commented Apr 20, 2025

sdruzkin Apr 20, 2025 •

edited

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steveburnett commented Apr 25, 2025

Reduce memory usage in reader by reset all underlying readers #24912

Reduce memory usage in reader by reset all underlying readers #24912

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chenyangfb commented Apr 14, 2025 • edited by sdruzkin Loading

Description

Impact

Test Plan

sdruzkin commented Apr 20, 2025

sdruzkin Apr 20, 2025 • edited Loading

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steveburnett commented Apr 25, 2025

chenyangfb commented Apr 14, 2025 •

edited by sdruzkin

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sdruzkin Apr 20, 2025 •

edited

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