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From "ASF GitHub Bot (Jira)" <j...@apache.org>
Subject [jira] [Work logged] (HIVE-21924) Split text files even if header/footer exists
Date Fri, 27 Sep 2019 09:18:02 GMT

     [ https://issues.apache.org/jira/browse/HIVE-21924?focusedWorklogId=319435&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-319435
]

ASF GitHub Bot logged work on HIVE-21924:
-----------------------------------------

                Author: ASF GitHub Bot
            Created on: 27/Sep/19 09:17
            Start Date: 27/Sep/19 09:17
    Worklog Time Spent: 10m 
      Work Description: sankarh commented on pull request #791: HIVE-21924
URL: https://github.com/apache/hive/pull/791#discussion_r328914761
 
 

 ##########
 File path: ql/src/java/org/apache/hadoop/hive/ql/io/SkippingTextInputFormat.java
 ##########
 @@ -0,0 +1,136 @@
+package org.apache.hadoop.hive.ql.io;
+
+import org.apache.hadoop.fs.FSDataInputStream;
+import org.apache.hadoop.fs.Path;
+import org.apache.hadoop.mapred.FileSplit;
+import org.apache.hadoop.mapred.JobConf;
+import org.apache.hadoop.mapred.TextInputFormat;
+
+import java.io.IOException;
+import java.util.ArrayDeque;
+import java.util.Map;
+import java.util.Queue;
+import java.util.concurrent.ConcurrentHashMap;
+
+/**
+ * SkippingInputFormat is a header/footer aware input format. It truncates
+ * splits identified by TextInputFormat. Header and footers are removed
+ * from the splits.
+ */
+public class SkippingTextInputFormat extends TextInputFormat {
+
+  private final Map<Path, Long> startIndexMap = new ConcurrentHashMap<Path, Long>();
+  private final Map<Path, Long> endIndexMap = new ConcurrentHashMap<Path, Long>();
+  private JobConf conf;
+  private int headerCount;
+  private int footerCount;
+
+  @Override
+  public void configure(JobConf conf) {
+    this.conf = conf;
+    super.configure(conf);
+  }
+
+  public void configure(JobConf conf, int headerCount, int footerCount) {
+    configure(conf);
+    this.headerCount = headerCount;
+    this.footerCount = footerCount;
+  }
+
+  @Override
+  protected FileSplit makeSplit(Path file, long start, long length, String[] hosts) {
+    long cachedStart = getCachedStartIndex(file);
+    long cachedEnd = getCachedEndIndex(file);
+    if (cachedStart > start + length) {
+      return new NullRowsInputFormat.DummyInputSplit(file);
+    } else if (cachedStart > start) {
+      length = length - (cachedStart - start);
+      start = cachedStart;
+    }
+    if (cachedEnd > -1 && cachedEnd < start) {
+      return new NullRowsInputFormat.DummyInputSplit(file);
+    } else if (cachedEnd < start + length) {
+      length = cachedEnd - start;
+    }
+    return super.makeSplit(file, start, length, hosts);
+  }
+
+  @Override
+  protected FileSplit makeSplit(Path file, long start, long length, String[] hosts, String[]
inMemoryHosts) {
+    long cachedStart = getCachedStartIndex(file);
+    long cachedEnd = getCachedEndIndex(file);
+    if (cachedStart > start + length) {
+      return new NullRowsInputFormat.DummyInputSplit(file);
+    } else if (cachedStart > start) {
+      length = length - (cachedStart - start);
+      start = cachedStart;
+    }
+    if (cachedEnd > - 1 && cachedEnd < start) {
+      return new NullRowsInputFormat.DummyInputSplit(file);
+    } else if (cachedEnd < start + length) {
+      length = cachedEnd - start;
+    }
+    return super.makeSplit(file, start, length, hosts, inMemoryHosts);
+  }
+
+  private long getCachedStartIndex(Path path) {
+    Long startIndexForFile = startIndexMap.get(path);
+    if (startIndexForFile == null) {
+      try {
+        FSDataInputStream fis = path.getFileSystem(conf).open(path);
+        for (int j = 0; j < headerCount; j++) {
+          fis.readLine();
+          // back 1 byte because readers skip the entire first row if split start is not
0
+          startIndexForFile = fis.getPos() - 1;
 
 Review comment:
   Can we move this outside the loop?
   Also, as per current logic, if data have only footer rows and headerCount=0, then startIndexForFile
will be null. Having this statement outside the loop would handle it.
 
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Issue Time Tracking
-------------------

    Worklog Id:     (was: 319435)
    Time Spent: 40m  (was: 0.5h)

> Split text files even if header/footer exists
> ---------------------------------------------
>
>                 Key: HIVE-21924
>                 URL: https://issues.apache.org/jira/browse/HIVE-21924
>             Project: Hive
>          Issue Type: Improvement
>          Components: File Formats
>    Affects Versions: 2.4.0, 4.0.0, 3.2.0
>            Reporter: Prasanth Jayachandran
>            Assignee: Mustafa Iman
>            Priority: Major
>              Labels: pull-request-available
>         Attachments: HIVE-21924.patch
>
>          Time Spent: 40m
>  Remaining Estimate: 0h
>
> https://github.com/apache/hive/blob/967a1cc98beede8e6568ce750ebeb6e0d048b8ea/ql/src/java/org/apache/hadoop/hive/ql/io/HiveInputFormat.java#L494-L503

> {code}
>     int headerCount = 0;
>     int footerCount = 0;
>     if (table != null) {
>       headerCount = Utilities.getHeaderCount(table);
>       footerCount = Utilities.getFooterCount(table, conf);
>       if (headerCount != 0 || footerCount != 0) {
>         // Input file has header or footer, cannot be splitted.
>         HiveConf.setLongVar(conf, ConfVars.MAPREDMINSPLITSIZE, Long.MAX_VALUE);
>       }
>     }
> {code}
> this piece of code makes the CSV (or any text files with header/footer) files not splittable
if header or footer is present. 
> If only header is present, we can find the offset after first line break and use that
to split. Similarly for footer, may be read few KB's of data at the end and find the last
line break offset. Use that to determine the data range which can be used for splitting. Few
reads during split generation are cheaper than not splitting the file at all.  



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