[jira] [Work logged] (HADOOP-17770) WASB : Support disabling buffered reads in positional reads

["ASF GitHub Bot (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HADOOP-17770?focusedWorklogId=621065&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-621065 ]

ASF GitHub Bot logged work on HADOOP-17770:
-------------------------------------------

                Author: ASF GitHub Bot
            Created on: 09/Jul/21 16:48
            Start Date: 09/Jul/21 16:48
    Worklog Time Spent: 10m 
      Work Description: surendralilhore commented on a change in pull request #3149:
URL: https://github.com/apache/hadoop/pull/3149#discussion_r667084512



##########
File path: hadoop-tools/hadoop-azure/src/main/java/org/apache/hadoop/fs/azure/NativeAzureFileSystem.java
##########
@@ -915,6 +922,33 @@ public synchronized int read(byte[] b, int off, int len) throws FileNotFoundExce
       }
     }
 
+    @Override
+    public int read(long position, byte[] buffer, int offset, int length)
+        throws IOException {
+      if (in instanceof PositionedReadable) {
+        try {
+          int result = ((PositionedReadable) this.in).read(position, buffer,
+              offset, length);
+          if (null != statistics && result > 0) {
+            statistics.incrementBytesRead(result);
+          }
+          return result;
+        } catch (IOException e) {
+          Throwable innerException = NativeAzureFileSystemHelper.checkForAzureStorageException(e);
+          if (innerException instanceof StorageException) {
+            LOG.error("Encountered Storage Exception for read on Blob : {}"
+                + " Exception details: {} Error Code : {}",
+                key, e, ((StorageException) innerException).getErrorCode());
+            if (NativeAzureFileSystemHelper.isFileNotFoundException((StorageException) innerException)) {
+              throw new FileNotFoundException(String.format("%s is not found", key));
+            }
+          }
+          throw e;
+        }
+      }
+      return super.read(position, buffer, offset, length);

Review comment:
       I think if "in" is not PositionedReadable steam then we should throw exception. We shouldn't change the meaning of read() API by calling super.read().
   
   **FSInputStream.read(long, byte[], int, int)** internally call **read(byte[], int, int)**, which is not positioned read API. This will change the current offset of a file.
   




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Issue Time Tracking
-------------------

    Worklog Id:     (was: 621065)
    Time Spent: 40m  (was: 0.5h)

> WASB : Support disabling buffered reads in positional reads
> -----------------------------------------------------------
>
>                 Key: HADOOP-17770
>                 URL: https://issues.apache.org/jira/browse/HADOOP-17770
>             Project: Hadoop Common
>          Issue Type: Improvement
>            Reporter: Anoop Sam John
>            Assignee: Anoop Sam John
>            Priority: Major
>              Labels: pull-request-available
>             Fix For: 3.4.0
>
>         Attachments: AvgLatency_0 cache hit.png, AvgLatency_50% cache hit.png, Throughput_0 cache hit.png, Throughput_50% cache hit.png
>
>          Time Spent: 40m
>  Remaining Estimate: 0h
>
> This is just like HADOOP-17038
> Right now it will do a seek to the position , read and then seek back to the old position. (As per the impl in the super class)
> In HBase kind of workloads we rely mostly on short preads. (like 64 KB size by default). So would be ideal to support a pure pos read API which will not even keep the data in a buffer but will only read the required data as what is asked for by the caller. (Not reading ahead more data as per the read size config)
> Allow an optional boolean config to be specified while opening file for read using which buffered pread can be disabled.
> FutureDataInputStreamBuilder openFile(Path path)



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