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HBASE-26169 Fix MapReduceBackupCopyJob.BackupDistCp.getKey() concatenates strings #3562

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HBASE-26169 Fix MapReduceBackupCopyJob.BackupDistCp.getKey() concatenates strings #3562

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HBASE-26169 Fix MapReduceBackupCopyJob.BackupDistCp.getKey() concaten…
skyguard1 Aug 5, 2021
ac718c5
Use collection to store path.getName() string
skyguard1 Aug 6, 2021
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10 changes: 7 additions & 3 deletions ...backup/src/main/java/org/apache/hadoop/hbase/backup/mapreduce/MapReduceBackupCopyJob.java
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Original file line number Diff line number Diff line change
Expand Up @@ -23,6 +23,8 @@
import java.lang.reflect.Method;
import java.math.BigDecimal;
import java.util.Arrays;
import java.util.Deque;
import java.util.LinkedList;
import java.util.List;
import java.util.Objects;

Expand Down Expand Up @@ -331,12 +333,14 @@ protected Path createInputFileListing(Job job) throws IOException {
private Text getKey(Path path) {
int level = conf.getInt(NUMBER_OF_LEVELS_TO_PRESERVE_KEY, 1);
int count = 0;
String relPath = "";
Deque<String> paths = new LinkedList<>();
StringBuilder relPath = new StringBuilder();
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It's not that obvious to me that using StringBuilder in this way is faster (looking at the jira, I assumed this is the purpose of the change) than simple string concatenation, because StringBuilder.insert() may involve multiple array copy.

How about instantiating StringBuilder with a capacity (=level) as parameter so that we don't need to re-allocate & copy arrays?

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@skyguard1 skyguard1 Aug 6, 2021 •
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But the length of path.getName() is not fixed, how to determine the initial capacity?
Unless the Path is traversed again and the length of the name is calculated, the performance will obviously not improve. Splicing strings in a loop will generate a new string each time. In my opinion, using StringBuilder will improve performance, thanks

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Maybe a possible way is to store the path name in a list and then concat the list of strings from tail to head?

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But is it acceptable to apply for the space of the collection and the time cost of traversing the collection again?

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@Apache9 I changed to use a collection to store strings, PTAL

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looks good to me. Thank you.

while (count++ < level) {
relPath = Path.SEPARATOR + path.getName() + relPath;
paths.addFirst(Path.SEPARATOR + path.getName());
path = path.getParent();
}
return new Text(relPath);
paths.forEach(relPath::append);
return new Text(relPath.toString());
}

private List<Path> getSourceFiles() throws NoSuchFieldException, SecurityException,
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