guiyanakuang commented on a change in pull request #810:
URL: https://github.com/apache/orc/pull/810#discussion_r682234526



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File path: java/core/src/java/org/apache/orc/impl/ReaderImpl.java
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@@ -569,7 +561,13 @@ public ReaderImpl(Path path, OrcFile.ReaderOptions 
options) throws IOException {
       this.rowIndexStride = tail.getFooter().getRowIndexStride();
       this.contentLength = tail.getFooter().getContentLength();
       this.numberOfRows = tail.getFooter().getNumberOfRows();
-      this.userMetadata = tail.getFooter().getMetadataList();
+      this.userMetadata = tail.getFooter().getMetadataList()
+              .stream().collect(Collectors.toMap(

Review comment:
       > Thank you for making a PR, @guiyanakuang . Do you think we can have a 
benchmark result for your claim?
   > 
   > > There may be performance problems if there are more userMetadata keys
   > 
   > cc @pgaref , @williamhyun
   
   Sorry for the late reply due to different time zones. I made a guess based 
on the time complexity of the algorithm and have not yet benchmarked it. 
getMetadataValue is used in compatibility checking and metadata merging, which 
would have an O(n^2) time complexity if used in a loop.




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