[8.x] Support 7x segments as archive in 8x / 9x

docs/changelog/125389.yaml

@@ -0,0 +1,6 @@
+pr: 125389
+summary: Support indices created in ESv6 and updated in ESV7 using different LuceneCodecs
+  as archive in current version.
+area: Search
+type: bug
+issues: []

x-pack/plugin/old-lucene-versions/src/main/java/org/elasticsearch/xpack/lucene/bwc/codecs/BWCCodec.java

@@ -7,7 +7,6 @@
 
 package org.elasticsearch.xpack.lucene.bwc.codecs;
 
-import org.apache.lucene.backward_codecs.lucene70.Lucene70Codec;
 import org.apache.lucene.codecs.Codec;
 import org.apache.lucene.codecs.FieldInfosFormat;
 import org.apache.lucene.codecs.FieldsConsumer;
@@ -18,6 +17,7 @@
 import org.apache.lucene.codecs.PostingsFormat;
 import org.apache.lucene.codecs.SegmentInfoFormat;
 import org.apache.lucene.codecs.TermVectorsFormat;
+import org.apache.lucene.codecs.perfield.PerFieldPostingsFormat;
 import org.apache.lucene.index.FieldInfo;
 import org.apache.lucene.index.FieldInfos;
 import org.apache.lucene.index.Fields;
@@ -27,7 +27,12 @@
 import org.apache.lucene.index.Terms;
 import org.apache.lucene.store.Directory;
 import org.apache.lucene.store.IOContext;
+import org.apache.lucene.util.Version;
 import org.elasticsearch.xpack.lucene.bwc.codecs.lucene70.BWCLucene70Codec;
+import org.elasticsearch.xpack.lucene.bwc.codecs.lucene80.BWCLucene80Codec;
+import org.elasticsearch.xpack.lucene.bwc.codecs.lucene84.BWCLucene84Codec;
+import org.elasticsearch.xpack.lucene.bwc.codecs.lucene86.BWCLucene86Codec;
+import org.elasticsearch.xpack.lucene.bwc.codecs.lucene87.BWCLucene87Codec;
 
 import java.io.IOException;
 import java.util.ArrayList;
@@ -39,55 +44,122 @@
  */
 public abstract class BWCCodec extends Codec {
 
+    private final FieldInfosFormat fieldInfosFormat;
+    private final SegmentInfoFormat segmentInfosFormat;
+    private final PostingsFormat postingsFormat;
+
     protected BWCCodec(String name) {
         super(name);
-    }
 
-    @Override
-    public NormsFormat normsFormat() {
-        throw new UnsupportedOperationException();
-    }
+        this.fieldInfosFormat = new FieldInfosFormat() {
+            final FieldInfosFormat wrappedFormat = originalFieldInfosFormat();
 
-    @Override
-    public TermVectorsFormat termVectorsFormat() {
-        throw new UnsupportedOperationException();
-    }
+            @Override
+            public FieldInfos read(Directory directory, SegmentInfo segmentInfo, String segmentSuffix, IOContext iocontext)
+                throws IOException {
+                return filterFields(wrappedFormat.read(directory, segmentInfo, segmentSuffix, iocontext));
+            }
 
-    @Override
-    public KnnVectorsFormat knnVectorsFormat() {
-        throw new UnsupportedOperationException();
-    }
+            @Override
+            public void write(Directory directory, SegmentInfo segmentInfo, String segmentSuffix, FieldInfos infos, IOContext context)
+                throws IOException {
+                wrappedFormat.write(directory, segmentInfo, segmentSuffix, infos, context);
+            }
+        };
+
+        this.segmentInfosFormat = new SegmentInfoFormat() {
+            final SegmentInfoFormat wrappedFormat = originalSegmentInfoFormat();
 
-    protected static SegmentInfoFormat wrap(SegmentInfoFormat wrapped) {
-        return new SegmentInfoFormat() {
             @Override
             public SegmentInfo read(Directory directory, String segmentName, byte[] segmentID, IOContext context) throws IOException {
-                return wrap(wrapped.read(directory, segmentName, segmentID, context));
+                return wrap(wrappedFormat.read(directory, segmentName, segmentID, context));
             }
 
             @Override
             public void write(Directory dir, SegmentInfo info, IOContext ioContext) throws IOException {
-                wrapped.write(dir, info, ioContext);
+                wrappedFormat.write(dir, info, ioContext);
             }
         };
-    }
 
-    protected static FieldInfosFormat wrap(FieldInfosFormat wrapped) {
-        return new FieldInfosFormat() {
+        this.postingsFormat = new PerFieldPostingsFormat() {
             @Override
-            public FieldInfos read(Directory directory, SegmentInfo segmentInfo, String segmentSuffix, IOContext iocontext)
-                throws IOException {
-                return filterFields(wrapped.read(directory, segmentInfo, segmentSuffix, iocontext));
-            }
-
-            @Override
-            public void write(Directory directory, SegmentInfo segmentInfo, String segmentSuffix, FieldInfos infos, IOContext context)
-                throws IOException {
-                wrapped.write(directory, segmentInfo, segmentSuffix, infos, context);
+            public PostingsFormat getPostingsFormatForField(String field) {
+                throw new UnsupportedOperationException("Old codecs can't be used for writing");
             }
         };
     }
 
+    @Override
+    public final FieldInfosFormat fieldInfosFormat() {
+        return fieldInfosFormat;
+    }
+
+    @Override
+    public final SegmentInfoFormat segmentInfoFormat() {
+        return segmentInfosFormat;
+    }
+
+    @Override
+    public PostingsFormat postingsFormat() {
+        return postingsFormat;
+    }
+
+    /**
+     * This method is not supported for archive indices and older codecs and will always throw an {@link UnsupportedOperationException}.
+     * This method is never called in practice, as we rewrite field infos to override the info about which features are present in
+     * the index. Even if norms are present, field info lies about it.
+     *
+     * @return nothing, as this method always throws an exception
+     * @throws UnsupportedOperationException always thrown to indicate that this method is not supported
+     */
+    @Override
+    public final NormsFormat normsFormat() {
+        throw new UnsupportedOperationException();
+    }
+
+    /**
+     * This method is not supported for archive indices and older codecs and will always throw an {@link UnsupportedOperationException}.
+     * This method is never called in practice, as we rewrite field infos to override the info about which features are present in
+     * the index. Even if term vectors are present, field info lies about it.
+     *
+     * @return nothing, as this method always throws an exception
+     * @throws UnsupportedOperationException always thrown to indicate that this method is not supported
+     */
+    @Override
+    public final TermVectorsFormat termVectorsFormat() {
+        throw new UnsupportedOperationException();
+    }
+
+    /**
+     * This method is not supported for archive indices and older codecs and will always throw an {@link UnsupportedOperationException}.
+     * The knn vectors can't be present because it is not supported yet in any of the lucene versions that we support for archive indices.
+     *
+     * @return nothing, as this method always throws an exception
+     * @throws UnsupportedOperationException always thrown to indicate that this method is not supported
+     */
+    @Override
+    public final KnnVectorsFormat knnVectorsFormat() {
+        throw new UnsupportedOperationException();
+    }
+
+    /**
+     * Returns the original {@link SegmentInfoFormat} used by this codec.
+     * This method should be implemented by subclasses to provide the specific
+     * {@link SegmentInfoFormat} that this codec is intended to use.
+     *
+     * @return the original {@link SegmentInfoFormat} used by this codec
+     */
+    protected abstract SegmentInfoFormat originalSegmentInfoFormat();
+
+    /**
+     * Returns the original {@link FieldInfosFormat} used by this codec.
+     * This method should be implemented by subclasses to provide the specific
+     * {@link FieldInfosFormat} that this codec is intended to use.
+     *
+     * @return the original {@link FieldInfosFormat} used by this codec
+     */
+    protected abstract FieldInfosFormat originalFieldInfosFormat();
+
     // mark all fields as no term vectors, no norms, no payloads, and no vectors.
     private static FieldInfos filterFields(FieldInfos fieldInfos) {
         List<FieldInfo> fieldInfoCopy = new ArrayList<>(fieldInfos.size());
@@ -119,15 +191,14 @@ private static FieldInfos filterFields(FieldInfos fieldInfos) {
     }
 
     public static SegmentInfo wrap(SegmentInfo segmentInfo) {
-        // special handling for Lucene70Codec (which is currently bundled with Lucene)
-        // Use BWCLucene70Codec instead as that one extends BWCCodec (similar to all other older codecs)
-        final Codec codec = segmentInfo.getCodec() instanceof Lucene70Codec ? new BWCLucene70Codec() : segmentInfo.getCodec();
+        Codec codec = getBackwardCompatibleCodec(segmentInfo.getCodec());
+
         final SegmentInfo segmentInfo1 = new SegmentInfo(
             segmentInfo.dir,
             // Use Version.LATEST instead of original version, otherwise SegmentCommitInfo will bark when processing (N-1 limitation)
             // TODO: perhaps store the original version information in attributes so that we can retrieve it later when needed?
-            org.apache.lucene.util.Version.LATEST,
-            org.apache.lucene.util.Version.LATEST,
+            Version.LATEST,
+            Version.LATEST,
             segmentInfo.name,
             segmentInfo.maxDoc(),
             segmentInfo.getUseCompoundFile(),
@@ -142,6 +213,28 @@ public static SegmentInfo wrap(SegmentInfo segmentInfo) {
         return segmentInfo1;
     }
 
+    /**
+     * Returns a backward-compatible codec for the given codec. If the codec is one of the known Lucene 8.x codecs,
+     * it returns a corresponding read-only backward-compatible codec. Otherwise, it returns the original codec.
+     * Lucene 8.x codecs are still shipped with the current version of Lucene.
+     * Earlier codecs we are providing directly they will also be read-only backward-compatible, but they don't require the renaming.
+     *
+     * This switch is only for indices created in ES 6.x, later written into in ES 7.x (Lucene 8.x). Indices created
+     * in ES 7.x can be read directly by ES if marked read-only, without going through archive indices.
+     */
+    private static Codec getBackwardCompatibleCodec(Codec codec) {
+        if (codec == null) return null;
+
+        return switch (codec.getClass().getSimpleName()) {
+            case "Lucene70Codec" -> new BWCLucene70Codec();
+            case "Lucene80Codec" -> new BWCLucene80Codec();
+            case "Lucene84Codec" -> new BWCLucene84Codec();
+            case "Lucene86Codec" -> new BWCLucene86Codec();
+            case "Lucene87Codec" -> new BWCLucene87Codec();
+            default -> codec;
+        };
+    }
+
     /**
      * In-memory postings format that shows no postings available.
      */

x-pack/plugin/old-lucene-versions/src/main/java/org/elasticsearch/xpack/lucene/bwc/codecs/lucene60/Lucene60Codec.java

@@ -44,8 +44,7 @@
  */
 @Deprecated
 public class Lucene60Codec extends BWCCodec {
-    private final FieldInfosFormat fieldInfosFormat = wrap(new Lucene60FieldInfosFormat());
-    private final SegmentInfoFormat segmentInfosFormat = wrap(new Lucene50SegmentInfoFormat());
+
     private final LiveDocsFormat liveDocsFormat = new Lucene50LiveDocsFormat();
     private final CompoundFormat compoundFormat = new Lucene50CompoundFormat();
     private final StoredFieldsFormat storedFieldsFormat;
@@ -68,18 +67,18 @@ public Lucene60Codec() {
     }
 
     @Override
-    public final StoredFieldsFormat storedFieldsFormat() {
-        return storedFieldsFormat;
+    protected FieldInfosFormat originalFieldInfosFormat() {
+        return new Lucene60FieldInfosFormat();
     }
 
     @Override
-    public final FieldInfosFormat fieldInfosFormat() {
-        return fieldInfosFormat;
+    protected SegmentInfoFormat originalSegmentInfoFormat() {
+        return new Lucene50SegmentInfoFormat();
     }
 
     @Override
-    public SegmentInfoFormat segmentInfoFormat() {
-        return segmentInfosFormat;
+    public final StoredFieldsFormat storedFieldsFormat() {
+        return storedFieldsFormat;
     }
 
     @Override

x-pack/plugin/old-lucene-versions/src/main/java/org/elasticsearch/xpack/lucene/bwc/codecs/lucene60/Lucene60MetadataOnlyPointsFormat.java

@@ -28,6 +28,7 @@
 import java.io.IOException;
 
 /**
+ * This is a fork of {@link org.apache.lucene.backward_codecs.lucene60.Lucene60PointsFormat}
  * Allows reading metadata only from Lucene 6.0 point format
  **/
 public class Lucene60MetadataOnlyPointsFormat extends PointsFormat {

x-pack/plugin/old-lucene-versions/src/main/java/org/elasticsearch/xpack/lucene/bwc/codecs/lucene60/Lucene60MetadataOnlyPointsReader.java

@@ -34,7 +34,10 @@
 import java.util.HashMap;
 import java.util.Map;
 
-/** Reads the metadata of point values previously written with Lucene60PointsWriter */
+/**
+ * This is a fork of {@link org.apache.lucene.backward_codecs.lucene60.Lucene60PointsReader}
+ * Reads the metadata of point values previously written with Lucene60PointsWriter
+ */
 public final class Lucene60MetadataOnlyPointsReader extends PointsReader {
     final IndexInput dataIn;
     final SegmentReadState readState;
@@ -105,7 +108,7 @@ public Lucene60MetadataOnlyPointsReader(SegmentReadState readState) throws IOExc
                 int fieldNumber = ent.getKey();
                 long fp = ent.getValue();
                 dataIn.seek(fp);
-                PointValues reader = new MetadataOnlyBKDReader(dataIn);
+                PointValues reader = new MetadataOnlyBKDReader(dataIn, false);
                 readers.put(fieldNumber, reader);
             }
 

x-pack/plugin/old-lucene-versions/src/main/java/org/elasticsearch/xpack/lucene/bwc/codecs/lucene60/MetadataOnlyBKDReader.java

@@ -47,7 +47,7 @@ public class MetadataOnlyBKDReader extends PointValues {
     final int docCount;
     final int version;
 
-    public MetadataOnlyBKDReader(IndexInput metaIn) throws IOException {
+    public MetadataOnlyBKDReader(IndexInput metaIn, boolean isVersionPost86) throws IOException {
         version = CodecUtil.checkHeader(metaIn, "BKD", VERSION_START, VERSION_CURRENT);
         final int numDims = metaIn.readVInt();
         final int numIndexDims;
@@ -85,6 +85,23 @@ public MetadataOnlyBKDReader(IndexInput metaIn) throws IOException {
 
         pointCount = metaIn.readVLong();
         docCount = metaIn.readVInt();
+
+        // The pre-8.6 code does not read the following fields that its standard Lucene counterpart does. After experimenting with the
+        // code, we got to the conclusion that these are the last fields being read, which are not needed in the metadata-only reader, and
+        // we can safely ignore them when loading the file. Although by coincidence, nothing breaks if we read a couple of VLongs, as long
+        // as some bytes are available to read.
+        //
+        // The extra reads have been introduced to process IndexInput created with Lucene86Codec+, where a new BKD format has been
+        // introduced. We have stricter checks around the header and footer starting from the 86 formats hence we do need to
+        // consume all the data input there but not in previous formats.
+        //
+        // For correctness, we added version checking here. If and only if, the version is 8.6 or higher, we read the additional fields.
+        if (isVersionPost86) {
+            metaIn.readVInt();
+            metaIn.readLong();
+            // The following fields are not used in this class, but we need to read them to advance the pointer
+            metaIn.readLong();
+        }
     }
 
     @Override

x-pack/plugin/old-lucene-versions/src/main/java/org/elasticsearch/xpack/lucene/bwc/codecs/lucene62/Lucene62Codec.java

@@ -44,8 +44,7 @@
  */
 @Deprecated
 public class Lucene62Codec extends BWCCodec {
-    private final FieldInfosFormat fieldInfosFormat = wrap(new Lucene60FieldInfosFormat());
-    private final SegmentInfoFormat segmentInfosFormat = wrap(new Lucene62SegmentInfoFormat());
+
     private final LiveDocsFormat liveDocsFormat = new Lucene50LiveDocsFormat();
     private final CompoundFormat compoundFormat = new Lucene50CompoundFormat();
     private final StoredFieldsFormat storedFieldsFormat;
@@ -68,18 +67,18 @@ public Lucene62Codec() {
     }
 
     @Override
-    public final StoredFieldsFormat storedFieldsFormat() {
-        return storedFieldsFormat;
+    protected FieldInfosFormat originalFieldInfosFormat() {
+        return new Lucene60FieldInfosFormat();
     }
 
     @Override
-    public final FieldInfosFormat fieldInfosFormat() {
-        return fieldInfosFormat;
+    protected SegmentInfoFormat originalSegmentInfoFormat() {
+        return new Lucene62SegmentInfoFormat();
     }
 
     @Override
-    public SegmentInfoFormat segmentInfoFormat() {
-        return segmentInfosFormat;
+    public final StoredFieldsFormat storedFieldsFormat() {
+        return storedFieldsFormat;
     }
 
     @Override