[GitHub] [hadoop] steveloughran commented on a change in pull request #3736: HADOOP-18028. improve S3 read speed using prefetching & caching

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steveloughran commented on a change in pull request #3736:
URL: https://github.com/apache/hadoop/pull/3736#discussion_r835515328



##########
File path: hadoop-tools/hadoop-aws/src/main/java/org/apache/hadoop/fs/s3a/read/S3EInputStream.java
##########
@@ -0,0 +1,240 @@
+/*
+ * 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
+ *
+ *   http://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.hadoop.fs.s3a.read;
+
+import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.classification.InterfaceStability;
+import org.apache.hadoop.fs.CanSetReadahead;
+import org.apache.hadoop.fs.FSExceptionMessages;
+import org.apache.hadoop.fs.FSInputStream;
+import org.apache.hadoop.fs.StreamCapabilities;
+import org.apache.hadoop.fs.common.Validate;
+import org.apache.hadoop.fs.s3a.S3AInputStream;
+import org.apache.hadoop.fs.s3a.S3AReadOpContext;
+import org.apache.hadoop.fs.s3a.S3ObjectAttributes;
+import org.apache.hadoop.fs.s3a.statistics.S3AInputStreamStatistics;
+import org.apache.hadoop.fs.statistics.IOStatistics;
+import org.apache.hadoop.fs.statistics.IOStatisticsSource;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.io.IOException;
+
+/**
+ * Enhanced {@code InputStream} for reading from S3.
+ *
+ * This implementation provides improved read throughput by asynchronously prefetching
+ * blocks of configurable size from the underlying S3 file.
+ */
+public class S3EInputStream

Review comment:
       i agree that saving time is generally the best action to prioritise, as if you are running in ec2 your cpu rental is a bigger cost. it does increase the risk of overloading the IO capacity of a shard in a bucket, but we have that with the current random IO implementation anyway




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