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From "ASF GitHub Bot (Jira)" <j...@apache.org>
Subject [jira] [Work logged] (HADOOP-17597) Add option to downgrade S3A rejection of Syncable to warning
Date Thu, 01 Apr 2021 14:02:00 GMT

     [ https://issues.apache.org/jira/browse/HADOOP-17597?focusedWorklogId=575518&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-575518
]

ASF GitHub Bot logged work on HADOOP-17597:
-------------------------------------------

                Author: ASF GitHub Bot
            Created on: 01/Apr/21 14:01
            Start Date: 01/Apr/21 14:01
    Worklog Time Spent: 10m 
      Work Description: mukund-thakur commented on a change in pull request #2801:
URL: https://github.com/apache/hadoop/pull/2801#discussion_r605678416



##########
File path: hadoop-tools/hadoop-aws/src/test/java/org/apache/hadoop/fs/s3a/ITestDowngradeSyncable.java
##########
@@ -0,0 +1,110 @@
+/*
+ * 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;
+
+import org.junit.Test;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.fs.FSDataOutputStream;
+import org.apache.hadoop.fs.Path;
+import org.apache.hadoop.fs.s3a.performance.AbstractS3ACostTest;
+import org.apache.hadoop.fs.statistics.IOStatistics;
+
+import static org.apache.hadoop.fs.s3a.Constants.DOWNGRADE_SYNCABLE_EXCEPTIONS;
+import static org.apache.hadoop.fs.s3a.S3ATestUtils.getTestBucketName;
+import static org.apache.hadoop.fs.s3a.S3ATestUtils.removeBucketOverrides;
+import static org.apache.hadoop.fs.statistics.IOStatisticAssertions.assertThatStatisticCounter;
+import static org.apache.hadoop.fs.statistics.IOStatisticsLogging.ioStatisticsToString;
+import static org.apache.hadoop.fs.statistics.StoreStatisticNames.OP_HFLUSH;
+import static org.apache.hadoop.fs.statistics.StoreStatisticNames.OP_HSYNC;
+
+
+public class ITestDowngradeSyncable extends AbstractS3ACostTest {
+
+  protected static final Logger LOG =
+      LoggerFactory.getLogger(ITestDowngradeSyncable.class);
+
+
+  public ITestDowngradeSyncable() {
+    super(false, true, false);
+  }
+
+  @Override
+  public Configuration createConfiguration() {
+    final Configuration conf = super.createConfiguration();
+    String bucketName = getTestBucketName(conf);
+    removeBucketOverrides(bucketName, conf,
+        DOWNGRADE_SYNCABLE_EXCEPTIONS);
+    conf.setBoolean(DOWNGRADE_SYNCABLE_EXCEPTIONS, true);
+    return conf;
+  }
+
+  @Test
+  public void testHFlushDowngrade() throws Throwable {

Review comment:
       nit: add describe

##########
File path: hadoop-tools/hadoop-aws/src/site/markdown/tools/hadoop-aws/troubleshooting_s3a.md
##########
@@ -1036,6 +1036,39 @@
 This includes resilient logging, HBase-style journaling
 and the like. The standard strategy here is to save to HDFS and then copy to S3.
 
+### <a name="syncable"></a> `UnsupportedOperationException` "S3A streams are
not Syncable. See HADOOP-17597."
+
+The application has tried to call either the `Syncable.hsync()` or `Syncable.hflush()`
+methods on an S3A output stream. This has been rejected because the
+connector isn't saving any data at all. The `Syncable` API, especially the
+`hsync()` call, are critical for applications such as HBase to safely
+persist data.
+
+The S3A connector throws an `UnsupportedOperationException` when these API calls
+are made, because the guarantees absolutely cannot be met: nothing is being flushed
+or saved.
+
+* Applications which intend to invoke the Syncable APIs call `hasCapability("hsync")` on
+  the stream to see if they are supported.
+* Or catch and downgrade `UnsupportedOperationException`.
+
+These recommendations _apply to all filesystems_. 
+
+To downgrade the S3A connector to simplying warning of the use of

Review comment:
       nit : typo simply warn the?

##########
File path: hadoop-tools/hadoop-aws/src/test/java/org/apache/hadoop/fs/s3a/TestS3ABlockOutputStream.java
##########
@@ -108,4 +126,31 @@ public void testCallingCloseAfterCallingAbort() throws Exception {
     // This will ensure abort() can be called with try-with-resource.
     stream.close();
   }
+
+
+  /**
+   * Unless configured to downgrade, the stream will raise exceptions on
+   * Syncable API calls.
+   */
+  @Test
+  public void testSyncableUnsupported() throws Exception {
+    intercept(UnsupportedOperationException.class, () -> stream.hflush());
+    intercept(UnsupportedOperationException.class, () -> stream.hsync());
+  }
+
+  /**
+   * When configured to downgrade, the stream downgrades on.

Review comment:
       nit: no fullstop in the end.

##########
File path: hadoop-tools/hadoop-aws/src/test/java/org/apache/hadoop/fs/s3a/ITestDowngradeSyncable.java
##########
@@ -0,0 +1,110 @@
+/*
+ * 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;
+
+import org.junit.Test;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.fs.FSDataOutputStream;
+import org.apache.hadoop.fs.Path;
+import org.apache.hadoop.fs.s3a.performance.AbstractS3ACostTest;
+import org.apache.hadoop.fs.statistics.IOStatistics;
+
+import static org.apache.hadoop.fs.s3a.Constants.DOWNGRADE_SYNCABLE_EXCEPTIONS;
+import static org.apache.hadoop.fs.s3a.S3ATestUtils.getTestBucketName;
+import static org.apache.hadoop.fs.s3a.S3ATestUtils.removeBucketOverrides;
+import static org.apache.hadoop.fs.statistics.IOStatisticAssertions.assertThatStatisticCounter;
+import static org.apache.hadoop.fs.statistics.IOStatisticsLogging.ioStatisticsToString;
+import static org.apache.hadoop.fs.statistics.StoreStatisticNames.OP_HFLUSH;
+import static org.apache.hadoop.fs.statistics.StoreStatisticNames.OP_HSYNC;
+
+
+public class ITestDowngradeSyncable extends AbstractS3ACostTest {
+
+  protected static final Logger LOG =
+      LoggerFactory.getLogger(ITestDowngradeSyncable.class);
+
+
+  public ITestDowngradeSyncable() {
+    super(false, true, false);
+  }
+
+  @Override
+  public Configuration createConfiguration() {
+    final Configuration conf = super.createConfiguration();
+    String bucketName = getTestBucketName(conf);
+    removeBucketOverrides(bucketName, conf,
+        DOWNGRADE_SYNCABLE_EXCEPTIONS);
+    conf.setBoolean(DOWNGRADE_SYNCABLE_EXCEPTIONS, true);
+    return conf;
+  }
+
+  @Test
+  public void testHFlushDowngrade() throws Throwable {
+    Path path = methodPath();
+    S3AFileSystem fs = getFileSystem();
+    final IOStatistics fsIoStats = fs.getIOStatistics();
+    assertThatStatisticCounter(fsIoStats, OP_HFLUSH)
+        .isEqualTo(0);
+
+    try (FSDataOutputStream out = fs.create(path, true)) {
+      out.write('1');
+      // must succeed
+      out.hflush();
+      // stats counter records the downgrade
+      IOStatistics iostats = out.getIOStatistics();
+      LOG.info("IOStats {}", ioStatisticsToString(iostats));
+      assertThatStatisticCounter(iostats, OP_HFLUSH)
+          .isEqualTo(1);
+      assertThatStatisticCounter(iostats, OP_HSYNC)
+          .isEqualTo(0);
+    }
+    // once closed. the FS will have its stats merged.
+    assertThatStatisticCounter(fsIoStats, OP_HFLUSH)
+        .isEqualTo(1);
+  }
+
+  @Test
+  public void testHSyncDowngrade() throws Throwable {

Review comment:
       nit: add describe test




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

    Worklog Id:     (was: 575518)
    Time Spent: 1h  (was: 50m)

> Add option to downgrade S3A rejection of Syncable to warning
> ------------------------------------------------------------
>
>                 Key: HADOOP-17597
>                 URL: https://issues.apache.org/jira/browse/HADOOP-17597
>             Project: Hadoop Common
>          Issue Type: Bug
>    Affects Versions: 3.3.1
>            Reporter: Steve Loughran
>            Assignee: Steve Loughran
>            Priority: Minor
>              Labels: pull-request-available
>          Time Spent: 1h
>  Remaining Estimate: 0h
>
> The Hadoop Filesystem Syncable API is intended to meet the requirements laid out in [StoneBraker81]
_Operating System Support for Database Management_
> bq.  The service required from an OS buffer manager is a selectedforce out which would
push the intentions list and the commit flag to disk in the proper order. Such a service is
not present in any buffer manager known to us.
> It's an expensive operation -so expensive that {{Syncable.hsync()}} isn't even called
on {{DFSOutputStream.close()}}. I
> Even though S3A does not manifest any data until close() is called, applications coming
from HDFS may call Syncable methods and expect to them to persist data with the durability
guarantees offered by HDFS.
> Since the output stream hardening of HADOOP-13327, S3A throws UnsupportedOperationException
to indicate that the synchronization semantics of Syncable absolutely cannot be met. 
> As a result, applications which have been calling the Syncable APIs are finding the call
failing. In the absence of exception handling to recognise that the durability semantics are
being met, they fail.
> If the user and the application actually expects data to be persisted, this is the correct
behaviour. The data cannot be persisted this way.
> If, however, they were calling this on HDFS more as a {{flush()}} than the full and expensive
DBMS-class persistence call, then this failure is unwelcome. The applications really needs
to catch the UnsupportedOperationException raised by S3A _or any other FS strictly reporting
failures_, report the problem and perform some other means of safe data storage
> Even better, they can use hasPathCapability on the FS or hasCapability() on the stream
to probe before even opening a file or trying to sync it. the hasCapability() on a stream
was actually implemented in Hadooop-2.x precisely to allow applications to identify when a
stream could not meet the guarantees (e.g some of the encrypted streams, file:// before HADOOP-13...)
> Until they can correct their code, I propose adding the option for s3a to downgrade
> fs.s3a.downgrade.syncable.exceptions 
> This will
> * Log once per process at WARN
> * downgrade the calls to noop() 
> * increment counters in S3A stats and IO stats of invocations of the Syncable methods.
This will allow for stats gathering to let us identify which applications need fixing in cloud
deployments
> Testing: copy the hsync tests but expect exceptions to be swallowed and stats to be collected
> Also: UnsupportedException text will link to this JIRA



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