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Merged
dlmarion merged 1 commit into from
Jun 30, 2026
+37 −3
Merged

Attempt at reducing GC memory usage when gathering candidates #6449

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33 changes: 33 additions & 0 deletions server/base/src/main/java/org/apache/accumulo/server/metadata/GcCandidateFilter.java
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Original file line number Diff line number Diff line change
@@ -0,0 +1,33 @@
/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* https://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing,
* software distributed under the License is distributed on an
* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
* KIND, either express or implied. See the License for the
* specific language governing permissions and limitations
* under the License.
*/
package org.apache.accumulo.server.metadata;

import org.apache.accumulo.core.data.Key;
import org.apache.accumulo.core.data.Value;
import org.apache.accumulo.core.iterators.Filter;
import org.apache.accumulo.core.metadata.schema.MetadataSchema.DeletesSection.SkewedKeyValue;

public class GcCandidateFilter extends Filter {

@Override
public boolean accept(Key k, Value v) {
return v.equals(SkewedKeyValue.NAME);
}

}
5 changes: 3 additions & 2 deletions server/base/src/main/java/org/apache/accumulo/server/metadata/ServerAmpleImpl.java
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Expand Up @@ -36,6 +36,7 @@
import org.apache.accumulo.core.client.BatchScanner;
import org.apache.accumulo.core.client.BatchWriter;
import org.apache.accumulo.core.client.IsolatedScanner;
import org.apache.accumulo.core.client.IteratorSetting;
import org.apache.accumulo.core.client.MutationsRejectedException;
import org.apache.accumulo.core.client.Scanner;
import org.apache.accumulo.core.client.TableNotFoundException;
Expand All @@ -60,7 +61,6 @@
import org.apache.accumulo.core.metadata.schema.ExternalCompactionId;
import org.apache.accumulo.core.metadata.schema.MetadataSchema.BlipSection;
import org.apache.accumulo.core.metadata.schema.MetadataSchema.DeletesSection;
import org.apache.accumulo.core.metadata.schema.MetadataSchema.DeletesSection.SkewedKeyValue;
import org.apache.accumulo.core.metadata.schema.MetadataSchema.ExternalCompactionSection;
import org.apache.accumulo.core.metadata.schema.MetadataSchema.ScanServerFileReferenceSection;
import org.apache.accumulo.core.metadata.schema.MetadataSchema.TabletsSection.BulkFileColumnFamily;
Expand Down Expand Up @@ -270,7 +270,8 @@ public Iterator<GcCandidate> getGcCandidates(DataLevel level) {
throw new RuntimeException(e);
}
scanner.setRange(range);
return scanner.stream().filter(entry -> entry.getValue().equals(SkewedKeyValue.NAME))
scanner.addScanIterator(new IteratorSetting(25, "gcCandidate", GcCandidateFilter.class));

@ddanielr ddanielr Jun 29, 2026

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Are we keeping track of the system iterator priorities being used?

I see the default value of the versioning iterator being set at 20, but that's just a hardcoded value.

accumulo/core/src/main/java/org/apache/accumulo/core/iteratorsImpl/IteratorConfigUtil.java

Lines 110 to 111 in 9d1377c

props.put(Property.TABLE_ITERATOR_PREFIX + iterScope.name() + ".vers",
"20," + VersioningIterator.class.getName());

Wondering if that initial value of 20 should be refactored into a system constant of DEFAULT_ITERATOR_PRIORITY.

@dlmarion dlmarion Jun 29, 2026

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Are we keeping track of the system iterator priorities being used?

I don't think there is a constant in 2.1, there might be a constant in 4.0. I can look for that.

@dlmarion dlmarion Jun 29, 2026

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I'm not seeing a constant. I see a literal 20 being used in main in IteratorConfigUtil.getInitialTableIteratorSettings

return scanner.stream()
.map(
entry -> new GcCandidate(DeletesSection.decodeRow(entry.getKey().getRow().toString()),
entry.getKey().getTimestamp()))
Expand Down
2 changes: 1 addition & 1 deletion server/gc/src/main/java/org/apache/accumulo/gc/GCRun.java
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Expand Up @@ -150,7 +150,7 @@ public List<GcCandidate> readCandidatesThatFitInMemory(Iterator<GcCandidate> can
// Converting the bytes to approximate number of characters for batch size.
long candidateBatchSize = getCandidateBatchSize() / 2;

List<GcCandidate> candidatesBatch = new ArrayList<>();
List<GcCandidate> candidatesBatch = new ArrayList<>(256);
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ddanielr marked this conversation as resolved.
batchCount.incrementAndGet();

while (candidates.hasNext()) {
Expand Down