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https://issues.apache.org/jira/browse/HADOOP-18190?focusedWorklogId=791412&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-791412
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ASF GitHub Bot logged work on HADOOP-18190:
-------------------------------------------

                Author: ASF GitHub Bot
            Created on: 15/Jul/22 13:23
            Start Date: 15/Jul/22 13:23
    Worklog Time Spent: 10m 
      Work Description: steveloughran commented on code in PR #4458:
URL: https://github.com/apache/hadoop/pull/4458#discussion_r922144050


##########
hadoop-tools/hadoop-aws/src/main/java/org/apache/hadoop/fs/s3a/Constants.java:
##########
@@ -674,6 +674,46 @@ private Constants() {
   public static final String STREAM_READ_GAUGE_INPUT_POLICY =
       "stream_read_gauge_input_policy";
 
+  /**
+   * Total number of prefetching operations executed.
+   */
+  public static final String STREAM_READ_PREFETCH_OPERATIONS

Review Comment:
   as you discussed, move to StreamStatisticNames in hadoop-common



##########
hadoop-tools/hadoop-aws/src/test/java/org/apache/hadoop/fs/common/TestBlockCache.java:
##########
@@ -38,7 +39,8 @@ public class TestBlockCache extends AbstractHadoopTestBase {
   @Test
   public void testArgChecks() throws Exception {
     // Should not throw.
-    BlockCache cache = new SingleFilePerBlockCache();
+    BlockCache cache =
+        new 
SingleFilePerBlockCache(EmptyS3AStatisticsContext.EMPTY_INPUT_STREAM_STATISTICS);

Review Comment:
   when we move to hadoop common the s3a classes won't be available. Add an 
empty implementation in this test package and use it





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

    Worklog Id:     (was: 791412)
    Time Spent: 1h  (was: 50m)

> s3a prefetching streams to collect iostats on prefetching operations
> --------------------------------------------------------------------
>
>                 Key: HADOOP-18190
>                 URL: https://issues.apache.org/jira/browse/HADOOP-18190
>             Project: Hadoop Common
>          Issue Type: Sub-task
>          Components: fs/s3
>    Affects Versions: 3.4.0
>            Reporter: Steve Loughran
>            Assignee: Ahmar Suhail
>            Priority: Major
>              Labels: pull-request-available
>          Time Spent: 1h
>  Remaining Estimate: 0h
>
> There is a lot more happening in reads, so there's a lot more data to collect 
> and publish in IO stats for us to view in a summary at the end of processes 
> as well as get from the stream while it is active.
> Some useful ones would seem to be:
> counters
>  * is in memory. using 0 or 1 here lets aggregation reports count total #of 
> memory cached files.
>  * prefetching operations executed
>  * errors during prefetching
> gauges
>  * number of blocks in cache
>  * total size of blocks
>  * active prefetches
> + active memory used
> duration tracking count/min/max/ave
>  * time to fetch a block
>  * time queued before the actual fetch begins
>  * time a reader is blocked waiting for a block fetch to complete
> and some info on cache use itself
>  * number of blocks discarded unread
>  * number of prefetched blocks later used
>  * number of backward seeks to a prefetched block
>  * number of forward seeks to a prefetched block
> the key ones I care about are
>  # memory consumption
>  # can we determine if cache is working (reads with cache hit) and when it is 
> not (misses, wasted prefetches)
>  # time blocked on executors
> The stats need to be accessible on a stream even when closed, and aggregated 
> into the FS. once we get per-thread stats contexts we can publish there too 
> and collect in worker threads for reporting in task commits



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