do string compression in StringCompressor instead of Tag

data-store/src/main/java/org/lucares/pdb/datastore/internal/DataStore.java

@@ -127,8 +127,9 @@ public class DataStore implements AutoCloseable {
         Tags.STRING_COMPRESSOR = StringCompressor.create(keyCompressionFile(storageBasePath));
         Tags.STRING_COMPRESSOR.put(ALL_DOCS_KEY);
         Tags.STRING_COMPRESSOR.put("");
-        TAG_ALL_DOCS = new Tag(ALL_DOCS_KEY, ""); // Tag(String, String) uses the StringCompressor internally, so it
+        TAG_ALL_DOCS = Tags.STRING_COMPRESSOR.createTag(ALL_DOCS_KEY, ""); // Tag(String, String) uses the
-                                                  // must be initialized after the string compressor has been created
+                                                                           // StringCompressor internally, so it
+        // must be initialized after the string compressor has been created
 
         diskStorage = new PartitionDiskStore(storageBasePath, "data.bs");
 
@@ -263,7 +264,7 @@ public class DataStore implements AutoCloseable {
 
         final Set<String> keys = new HashSet<>();
 
-        final Tag keyPrefix = new Tag("", ""); // will find everything
+        final Tag keyPrefix = Tags.STRING_COMPRESSOR.createTag("", ""); // will find everything
 
         final PartitionIdSource partitionIdSource = new DatePartitioner(dateRange);
         tagToDocsId.visitValues(partitionIdSource, keyPrefix, (tags, __) -> keys.add(tags.getKeyAsString()));

data-store/src/main/java/org/lucares/pdb/datastore/internal/QueryCompletionIndex.java

@@ -154,8 +154,8 @@ public class QueryCompletionIndex implements AutoCloseable {
 
         public TwoTags(final String fieldB, final String fieldA, final String valueA, final String valueB) {
 
-            tagA = new Tag(fieldA, valueA);
+            tagA = Tags.STRING_COMPRESSOR.createTag(fieldA, valueA);
-            tagB = new Tag(fieldB, valueB);
+            tagB = Tags.STRING_COMPRESSOR.createTag(fieldB, valueB);
         }
 
         public Tag getTagA() {

data-store/src/main/java/org/lucares/pdb/datastore/internal/TagEncoderDecoder.java

@@ -38,17 +38,17 @@ class TagEncoderDecoder implements EncoderDecoder<Tag> {
         switch (compressedStrings.size()) {
         case 0:
 
-            result = new Tag("", "");
+            result = Tags.STRING_COMPRESSOR.createTag("", "");
             break;
         case 1:
             final String k = Tags.STRING_COMPRESSOR.get((int) compressedStrings.get(0));
-            result = new Tag(k, "");
+            result = Tags.STRING_COMPRESSOR.createTag(k, "");
 
             break;
         case 2:
             final String key = Tags.STRING_COMPRESSOR.get((int) compressedStrings.get(0));
             final String value = Tags.STRING_COMPRESSOR.get((int) compressedStrings.get(1));
-            result = new Tag(key, value);
+            result = Tags.STRING_COMPRESSOR.createTag(key, value);
             break;
         default:
             throw new IllegalStateException("too many values: " + compressedStrings);

data-store/src/main/java/org/lucares/pdb/datastore/lang/ExpressionToDocIdVisitor.java

@@ -10,6 +10,7 @@ import java.util.stream.Collectors;
 import org.lucares.collections.LongList;
 import org.lucares.pdb.api.DateTimeRange;
 import org.lucares.pdb.api.Tag;
+import org.lucares.pdb.api.Tags;
 import org.lucares.pdb.blockstorage.LongStreamFile;
 import org.lucares.pdb.datastore.internal.DataStore;
 import org.lucares.pdb.datastore.internal.DatePartitioner;
@@ -148,27 +149,29 @@ public class ExpressionToDocIdVisitor extends ExpressionVisitor<PartitionLongLis
         final Set<ParititionId> availablePartitionIds = keyToValueToDocId.getAvailablePartitionIds(datePartitioner);
         for (final ParititionId partitionId : availablePartitionIds) {
             final List<LongList> docIdsForPartition = new ArrayList<>();
-            keyToValueToDocId.visitValues(partitionId, new Tag(propertyName, ""), (tags, blockOffsetToDocIds) -> {
+            keyToValueToDocId.visitValues(partitionId, Tags.STRING_COMPRESSOR.createTag(propertyName, ""),
-                if (valuePattern.matcher(tags.getValueAsString()).matches()) {
+                    (tags, blockOffsetToDocIds) -> {
-                    try (final LongStreamFile bsFile = diskStorage.streamExistingFile(blockOffsetToDocIds,
+                        if (valuePattern.matcher(tags.getValueAsString()).matches()) {
-                            partitionId)) {
+                            try (final LongStreamFile bsFile = diskStorage.streamExistingFile(blockOffsetToDocIds,
+                                    partitionId)) {
 
-                        // We know that all LongLists coming from a BSFile are sorted, non-overlapping
+                                // We know that all LongLists coming from a BSFile are sorted, non-overlapping
-                        // and increasing, that means we can just concatenate them and get a sorted
+                                // and increasing, that means we can just concatenate them and get a sorted
-                        // list.
+                                // list.
-                        final List<LongList> longLists = bsFile.streamOfLongLists().collect(Collectors.toList());
+                                final List<LongList> longLists = bsFile.streamOfLongLists()
-                        final LongList concatenatedLists = concatenateLists(longLists);
+                                        .collect(Collectors.toList());
+                                final LongList concatenatedLists = concatenateLists(longLists);
 
-                        Preconditions.checkTrue(concatenatedLists.isSorted(),
+                                Preconditions.checkTrue(concatenatedLists.isSorted(),
-                                "The LongLists containing document ids must be sorted, "
+                                        "The LongLists containing document ids must be sorted, "
-                                        + "non-overlapping and increasing, so that the concatenation "
+                                                + "non-overlapping and increasing, so that the concatenation "
-                                        + "is sorted. This is guaranteed by the fact that document ids "
+                                                + "is sorted. This is guaranteed by the fact that document ids "
-                                        + "are generated in monotonically increasing order.");
+                                                + "are generated in monotonically increasing order.");
 
-                        docIdsForPartition.add(concatenatedLists);
+                                docIdsForPartition.add(concatenatedLists);
-                    }
+                            }
-                }
+                        }
-            });
+                    });
 
             final LongList mergedDocsIdsForPartition = LongList.union(docIdsForPartition);
             result.put(partitionId, mergedDocsIdsForPartition);

data-store/src/main/java/org/lucares/pdb/datastore/lang/FindValuesForQueryCompletion.java

@@ -7,6 +7,7 @@ import java.util.TreeSet;
 
 import org.lucares.pdb.api.DateTimeRange;
 import org.lucares.pdb.api.Tag;
+import org.lucares.pdb.api.Tags;
 import org.lucares.pdb.datastore.internal.GlobMatcher;
 import org.lucares.pdb.datastore.internal.QueryCompletionIndex;
 import org.lucares.pdb.datastore.lang.Expression.And;
@@ -62,7 +63,7 @@ public class FindValuesForQueryCompletion extends ExpressionVisitor<SortedSet<St
                     result = new TreeSet<>();
 
                     for (final String v : valuesA) {
-                        final Tag tagA = new Tag(fieldA, v);
+                        final Tag tagA = Tags.STRING_COMPRESSOR.createTag(fieldA, v);
                         final SortedSet<String> tmp = index.find(dateTimeRange, tagA, field);
                         result.addAll(tmp);
                     }
@@ -150,7 +151,7 @@ public class FindValuesForQueryCompletion extends ExpressionVisitor<SortedSet<St
             }
 
             final Property property = (Property) expression.getExpression();
-            final Tag tag = new Tag(property.getField(), property.getValueAsString());
+            final Tag tag = Tags.STRING_COMPRESSOR.createTag(property.getField(), property.getValueAsString());
 
             final SortedSet<String> valuesNotForField = index.findAllValuesNotForField(dateTimeRange, tag, field);
             final SortedSet<String> valuesForField = index.find(dateTimeRange, tag, field);

data-store/src/test/java/org/lucares/pdb/datastore/internal/QueryCompletionIndexTest.java

@@ -10,14 +10,13 @@ import java.util.SortedSet;
 import java.util.TreeSet;
 
 import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.Assertions;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 import org.lucares.pdb.api.DateTimeRange;
 import org.lucares.pdb.api.StringCompressor;
-import org.lucares.pdb.api.Tag;
 import org.lucares.pdb.api.Tags;
 import org.lucares.pdb.api.UniqueStringIntegerPairs;
-import org.junit.jupiter.api.Assertions;
 import org.lucares.utils.file.FileUtils;
 
 public class QueryCompletionIndexTest {
@@ -54,14 +53,14 @@ public class QueryCompletionIndexTest {
 
             // all firstnames where lastname=Doe are returned sorted alphabetically.
             // tags A and B match
-            final SortedSet<String> firstnamesWithLastnameDoe = index.find(dateRange, new Tag("lastname", "Doe"),
+            final SortedSet<String> firstnamesWithLastnameDoe = index.find(dateRange,
-                    "firstname");
+                    Tags.STRING_COMPRESSOR.createTag("lastname", "Doe"), "firstname");
             Assertions.assertEquals(new TreeSet<>(Set.of("Jane", "John")), firstnamesWithLastnameDoe);
 
             // no duplicates are returned:
             // tags A and C match firstname=John, but both have country=Atlantis
-            final SortedSet<String> countryWithFirstnameJohn = index.find(dateRange, new Tag("firstname", "John"),
+            final SortedSet<String> countryWithFirstnameJohn = index.find(dateRange,
-                    "country");
+                    Tags.STRING_COMPRESSOR.createTag("firstname", "John"), "country");
             Assertions.assertEquals(new TreeSet<>(Arrays.asList("Atlantis")), countryWithFirstnameJohn);
 
             // findAllValuesForField sorts alphabetically

pdb-api/src/main/java/org/lucares/pdb/api/StringCompressor.java

@@ -39,4 +39,16 @@ public class StringCompressor {
         return integer != null ? integer : -1;
     }
 
+    /**
+     * Create a new {@link Tag} for the given field and value.
+     *
+     * @param field the field
+     * @param value the value
+     */
+    public Tag createTag(final String field, final String value) {
+        final int f = field != null ? Tags.STRING_COMPRESSOR.getIfPresent(field) : -1;
+        final int v = value != null ? Tags.STRING_COMPRESSOR.getIfPresent(value) : -1;
+        return new Tag(f, v);
+    }
+
 }

pdb-api/src/main/java/org/lucares/pdb/api/Tag.java

@@ -22,17 +22,6 @@ public class Tag implements Comparable<Tag> {
         this.value = value;
     }
 
-    /**
-     * Create a new {@link Tag} for the given field and value.
-     *
-     * @param field the field
-     * @param value the value
-     */
-    public Tag(final String field, final String value) {
-        this.field = field != null ? Tags.STRING_COMPRESSOR.getIfPresent(field) : -1;
-        this.value = value != null ? Tags.STRING_COMPRESSOR.getIfPresent(value) : -1;
-    }
-
     @Override
     public int compareTo(final Tag o) {
 

pdb-api/src/test/java/org/lucares/memory/MemoryScale.java

@@ -7,7 +7,6 @@ import java.util.LinkedHashMap;
 import java.util.Map;
 
 import org.lucares.pdb.api.StringCompressor;
-import org.lucares.pdb.api.Tag;
 import org.lucares.pdb.api.Tags;
 import org.lucares.pdb.api.TagsBuilder;
 import org.lucares.pdb.api.UniqueStringIntegerPairs;
@@ -74,7 +73,7 @@ public class MemoryScale {
     }
 
     private static Object createTag() {
-        return new Tag("", "");
+        return Tags.STRING_COMPRESSOR.createTag("", "");
     }
 
     private static Object createTags0() {