[LUCENE-8662] Change TermsEnum.seekExact(BytesRef) to abstract + delegate seekExact(BytesRef) in FilterLeafReader.FilterTermsEnum

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 5.5.5, 6.6.5, 7.6, 8.0
• Fix Version/s: 8.0
• Component/s: core/search
• Labels: query
• Lucene Fields: New
• Assignee: Unassigned
• Reporter: jefferyyuan
• Created: 28/Jan/19 20:52
• Updated: 22/Sep/22 14:10
• Resolved: 08/Feb/19 23:27

Description

Recently in our production, we found that Solr uses a lot of memory(more than 10g) during recovery or commit for a small index (3.5gb)
The stack trace is:

 

Thread 0x4d4b115c0 
  at org.apache.lucene.store.DataInput.readVInt()I (DataInput.java:125) 
  at org.apache.lucene.codecs.blocktree.SegmentTermsEnumFrame.loadBlock()V (SegmentTermsEnumFrame.java:157) 
  at org.apache.lucene.codecs.blocktree.SegmentTermsEnumFrame.scanToTermNonLeaf(Lorg/apache/lucene/util/BytesRef;Z)Lorg/apache/lucene/index/TermsEnum$SeekStatus; (SegmentTermsEnumFrame.java:786) 
  at org.apache.lucene.codecs.blocktree.SegmentTermsEnumFrame.scanToTerm(Lorg/apache/lucene/util/BytesRef;Z)Lorg/apache/lucene/index/TermsEnum$SeekStatus; (SegmentTermsEnumFrame.java:538) 
  at org.apache.lucene.codecs.blocktree.SegmentTermsEnum.seekCeil(Lorg/apache/lucene/util/BytesRef;)Lorg/apache/lucene/index/TermsEnum$SeekStatus; (SegmentTermsEnum.java:757) 
  at org.apache.lucene.index.FilterLeafReader$FilterTermsEnum.seekCeil(Lorg/apache/lucene/util/BytesRef;)Lorg/apache/lucene/index/TermsEnum$SeekStatus; (FilterLeafReader.java:185) 
  at org.apache.lucene.index.TermsEnum.seekExact(Lorg/apache/lucene/util/BytesRef;)Z (TermsEnum.java:74) 
  at org.apache.solr.search.SolrIndexSearcher.lookupId(Lorg/apache/lucene/util/BytesRef;)J (SolrIndexSearcher.java:823) 
  at org.apache.solr.update.VersionInfo.getVersionFromIndex(Lorg/apache/lucene/util/BytesRef;)Ljava/lang/Long; (VersionInfo.java:204) 
  at org.apache.solr.update.UpdateLog.lookupVersion(Lorg/apache/lucene/util/BytesRef;)Ljava/lang/Long; (UpdateLog.java:786) 
  at org.apache.solr.update.VersionInfo.lookupVersion(Lorg/apache/lucene/util/BytesRef;)Ljava/lang/Long; (VersionInfo.java:194) 
  at org.apache.solr.update.processor.DistributedUpdateProcessor.versionAdd(Lorg/apache/solr/update/AddUpdateCommand;)Z (DistributedUpdateProcessor.java:1051)  

We reproduced the problem locally with the following code using Lucene code.

public static void main(String[] args) throws IOException {
  FSDirectory index = FSDirectory.open(Paths.get("the-index"));
  try (IndexReader reader = new   ExitableDirectoryReader(DirectoryReader.open(index),
new QueryTimeoutImpl(1000 * 60 * 5))) {
    String id = "the-id";

    BytesRef text = new BytesRef(id);
    for (LeafReaderContext lf : reader.leaves()) {
      TermsEnum te = lf.reader().terms("id").iterator();
      System.out.println(te.seekExact(text));
    }
  }
}

 

I added System.out.println("ord: " + ord); in codecs.blocktree.SegmentTermsEnum.getFrame(int).

Please check the attached output of test program.txt. 

 

We found out the root cause:

we didn't implement seekExact(BytesRef) method in FilterLeafReader.FilterTerms, so it uses the base class TermsEnum.seekExact(BytesRef) implementation which is very inefficient in this case.

public boolean seekExact(BytesRef text) throws IOException {
  return seekCeil(text) == SeekStatus.FOUND;
}

The fix is simple, just override seekExact(BytesRef) method in FilterLeafReader.FilterTerms

@Override
public boolean seekExact(BytesRef text) throws IOException {
  return in.seekExact(text);
}

Issue Links

• is related to: LUCENE-8292 Fix FilterLeafReader.FilterTermsEnum to delegate all seekExact methods
• links to: GitHub Pull Request #551