feat: Delay reading from parquet file when creating table and column location

engine/table/src/main/java/io/deephaven/engine/table/impl/locations/TableLocation.java

@@ -127,7 +127,8 @@ interface Listener extends BasicTableDataListener {
 
     /**
      * @param name The column name
-     * @return The ColumnLocation for the defined column under this table location
+     * @return The ColumnLocation for the defined column under this table location. The exact same ColumnLocation object
+     *         should be returned for the same column name.
      */
     @NotNull
     ColumnLocation getColumnLocation(@NotNull CharSequence name);

engine/table/src/main/java/io/deephaven/engine/table/impl/locations/impl/AbstractTableLocation.java

@@ -94,12 +94,12 @@ public final Object getStateLock() {
     }
 
     @Override
-    public final RowSet getRowSet() {
+    public RowSet getRowSet() {
         return state.getRowSet();
     }
 
     @Override
-    public final long getSize() {
+    public long getSize() {
         return state.getSize();
     }
 

engine/table/src/main/java/io/deephaven/engine/table/impl/sources/regioned/RegionedColumnSourceManager.java

@@ -603,7 +603,9 @@ private class IncludedTableLocationEntry implements Comparable<IncludedTableLoca
         // New regions indices are assigned in order of insertion, starting from 0 with no re-use of removed indices.
         // If this logic changes, the `getTableAttributes()` logic needs to be updated.
         private final int regionIndex = nextRegionIndex++;
-        private final List<ColumnLocationState<?>> columnLocationStates = new ArrayList<>();
+
+        // Collection of column sources for which we have added a region, useful for invalidating together
+        private final Collection<RegionedColumnSource<?>> regionedColumnSources = new ArrayList<>();
 
         /**
          * RowSet in the region's space, not the table's space.
@@ -631,13 +633,11 @@ private void processInitial(final RowSetBuilderSequential addedRowSetBuilder, fi
                     .appendRange(regionFirstKey + subRegionFirstKey, regionFirstKey + subRegionLastKey));
 
             for (final ColumnDefinition<?> columnDefinition : columnDefinitions) {
-                // noinspection unchecked,rawtypes
-                final ColumnLocationState<?> state = new ColumnLocationState(
-                        columnDefinition,
-                        columnSources.get(columnDefinition.getName()),
-                        location.getColumnLocation(columnDefinition.getName()));
-                columnLocationStates.add(state);
-                state.regionAllocated(regionIndex);
+                final RegionedColumnSource<?> regionedColumnSource = columnSources.get(columnDefinition.getName());
+                final ColumnLocation columnLocation = location.getColumnLocation(columnDefinition.getName());
+                Assert.eq(regionIndex, "regionIndex", regionedColumnSource.addRegion(columnDefinition, columnLocation),
+                        "regionedColumnSource.addRegion((definition, location)");
+                regionedColumnSources.add(regionedColumnSource);
             }
 
             rowSetAtLastUpdate = initialRowSet;
@@ -710,7 +710,7 @@ private boolean pollUpdates(final RowSetBuilderSequential addedRowSetBuilder) {
         }
 
         private void invalidate() {
-            columnLocationStates.forEach(cls -> cls.source.invalidateRegion(regionIndex));
+            regionedColumnSources.forEach(source -> source.invalidateRegion(regionIndex));
         }
 
         @Override
@@ -734,30 +734,6 @@ public ImmutableTableLocationKey getKey(
                 }
             };
 
-    /**
-     * Batches up a definition, source, and location for ease of use. Implements grouping maintenance.
-     */
-    private static class ColumnLocationState<T> {
-
-        protected final ColumnDefinition<T> definition;
-        protected final RegionedColumnSource<T> source;
-        protected final ColumnLocation location;
-
-        private ColumnLocationState(
-                ColumnDefinition<T> definition,
-                RegionedColumnSource<T> source,
-                ColumnLocation location) {
-            this.definition = definition;
-            this.source = source;
-            this.location = location;
-        }
-
-        private void regionAllocated(final int regionIndex) {
-            Assert.eq(regionIndex, "regionIndex", source.addRegion(definition, location),
-                    "source.addRegion((definition, location)");
-        }
-    }
-
     public Map<String, Object> getTableAttributes(
             @NotNull TableUpdateMode tableUpdateMode,
             @NotNull TableUpdateMode tableLocationUpdateMode) {

extensions/parquet/table/src/main/java/io/deephaven/parquet/table/location/ParquetColumnLocation.java

@@ -39,6 +39,8 @@
 import java.math.BigInteger;
 import java.time.Instant;
 import java.util.Arrays;
+import java.util.Collections;
+import java.util.List;
 import java.util.Optional;
 import java.util.function.Function;
 import java.util.function.LongFunction;
@@ -58,13 +60,25 @@ final class ParquetColumnLocation<ATTR extends Values> extends AbstractColumnLoc
     private static final int MAX_PAGE_CACHE_SIZE = Configuration.getInstance()
             .getIntegerForClassWithDefault(ParquetColumnLocation.class, "maxPageCacheSize", 8192);
 
+    private final String columnName;
     private final String parquetColumnName;
+
+
+    private volatile boolean readersInitialized;
+
+    // Access to following variables must be guarded by initializeReaders()
     /**
      * Factory object needed for deferred initialization of the remaining fields. Reference serves as a barrier to
-     * ensure visibility of the derived fields.
+     * ensure visibility of the derived fields. We delay initializing this field till we need to read the column data.
      */
     private volatile ColumnChunkReader[] columnChunkReaders;
 
+    /**
+     * Whether the column location actually exists.
+     */
+    private boolean exists;
+    // -----------------------------------------------------------------------
+
     // We should consider moving this to column level if needed. Column-location level likely allows more parallelism.
     private volatile PageCache<ATTR> pageCache;
 
@@ -77,16 +91,34 @@ final class ParquetColumnLocation<ATTR extends Values> extends AbstractColumnLoc
      *
      * @param tableLocation The table location enclosing this column location
      * @param parquetColumnName The Parquet file column name
-     * @param columnChunkReaders The {@link ColumnChunkReader column chunk readers} for this location
      */
     ParquetColumnLocation(
             @NotNull final ParquetTableLocation tableLocation,
             @NotNull final String columnName,
-            @NotNull final String parquetColumnName,
-            @Nullable final ColumnChunkReader[] columnChunkReaders) {
+            @NotNull final String parquetColumnName) {
         super(tableLocation, columnName);
+        this.columnName = columnName;
         this.parquetColumnName = parquetColumnName;
-        this.columnChunkReaders = columnChunkReaders;
+        this.readersInitialized = false;
+    }
+
+    private void initializeReaders() {
+        if (readersInitialized) {
+            return;
+        }
+        synchronized (this) {
+            if (readersInitialized) {
+                return;
+            }
+            final String[] columnPath = tl().getParquetColumnNameToPath().get(parquetColumnName);
+            final List<String> nameList =
+                    columnPath == null ? Collections.singletonList(parquetColumnName) : Arrays.asList(columnPath);
+            final ColumnChunkReader[] columnChunkReaders = Arrays.stream(tl().getRowGroupReaders())
+                    .map(rgr -> rgr.getColumnChunk(columnName, nameList)).toArray(ColumnChunkReader[]::new);
+            exists = Arrays.stream(columnChunkReaders).anyMatch(ccr -> ccr != null && ccr.numRows() > 0);
+            this.columnChunkReaders = exists ? columnChunkReaders : null;
+            readersInitialized = true;
+        }
     }
 
     private PageCache<ATTR> ensurePageCache() {
@@ -114,10 +146,8 @@ public String getImplementationName() {
 
     @Override
     public boolean exists() {
-        // If we see a null columnChunkReaders array, either we don't exist or we are guaranteed to
-        // see a non-null
-        // pageStores array
-        return columnChunkReaders != null || pageStores != null;
+        initializeReaders();
+        return exists;
     }
 
     private ParquetTableLocation tl() {
@@ -258,7 +288,7 @@ private <TYPE> ColumnRegionObject<TYPE, ATTR> makeSingleColumnRegionObject(
      * @return The page stores
      */
     @NotNull
-    public ColumnChunkPageStore<ATTR>[] getPageStores(
+    private ColumnChunkPageStore<ATTR>[] getPageStores(
             @NotNull final ColumnDefinition<?> columnDefinition) {
         fetchValues(columnDefinition);
         return pageStores;
@@ -270,7 +300,7 @@ public ColumnChunkPageStore<ATTR>[] getPageStores(
      * @param columnDefinition The {@link ColumnDefinition} used to lookup type information
      * @return The dictionary values chunk suppliers, or null if none exist
      */
-    public Supplier<Chunk<ATTR>>[] getDictionaryChunkSuppliers(
+    private Supplier<Chunk<ATTR>>[] getDictionaryChunkSuppliers(
             @NotNull final ColumnDefinition<?> columnDefinition) {
         fetchValues(columnDefinition);
         return dictionaryChunkSuppliers;
@@ -291,6 +321,7 @@ private ColumnChunkPageStore<DictionaryKeys>[] getDictionaryKeysPageStores(
 
     @SuppressWarnings("unchecked")
     private void fetchValues(@NotNull final ColumnDefinition<?> columnDefinition) {
+        initializeReaders();
         if (columnChunkReaders == null) {
             return;
         }