chore(sql): fix occasional failures with first()/last()/first_not_nul…

…l()/last_not_null() direct string function (#4324)

core/src/main/java/io/questdb/cairo/RecoverVarIndex.java

@@ -80,7 +80,8 @@ protected void doReindex(
                     ff,
                     path.$(),
                     maxOffset,
-                    MemoryTag.MMAP_DEFAULT
+                    MemoryTag.MMAP_DEFAULT,
+                    false
             )) {
 
                 path.trimTo(colNameLen).put(".i");

core/src/main/java/io/questdb/cairo/TableReader.java

@@ -842,7 +842,7 @@ private MemoryMR openOrCreateMemory(
         if (mem != null && mem != NullMemoryMR.INSTANCE) {
             mem.of(ff, path, columnSize, columnSize, MemoryTag.MMAP_TABLE_READER);
         } else {
-            mem = Vm.getMRInstance(ff, path, columnSize, MemoryTag.MMAP_TABLE_READER);
+            mem = Vm.getMRInstance(ff, path, columnSize, MemoryTag.MMAP_TABLE_READER, true);
             columns.setQuick(primaryIndex, mem);
         }
         return mem;

core/src/main/java/io/questdb/cairo/TableReaderRecord.java

@@ -30,7 +30,6 @@
 import io.questdb.std.Long256;
 import io.questdb.std.Rows;
 import io.questdb.std.str.CharSink;
-import io.questdb.std.str.DirectCharSequence;
 import io.questdb.std.str.Sinkable;
 import io.questdb.std.str.Utf8Sequence;
 import org.jetbrains.annotations.NotNull;
@@ -100,18 +99,6 @@ public char getChar(int col) {
         return reader.getColumn(absoluteColumnIndex).getChar(offset);
     }
 
-    @Override
-    public DirectCharSequence getDirectStr(int col) {
-        final long recordIndex = getAdjustedRecordIndex(col) * Long.BYTES;
-        final int absoluteColumnIndex = ifOffsetNegThen0ElseValue(
-                recordIndex,
-                TableReader.getPrimaryColumnIndex(columnBase, col)
-        );
-        return reader.getColumn(absoluteColumnIndex).getDirectStr(
-                reader.getColumn(absoluteColumnIndex + 1).getLong(recordIndex)
-        );
-    }
-
     @Override
     public double getDouble(int col) {
         final long offset = getAdjustedRecordIndex(col) * Double.BYTES;
@@ -310,12 +297,14 @@ public long getUpdateRowId() {
         return getRowId();
     }
 
-    @Override @Nullable
+    @Override
+    @Nullable
     public Utf8Sequence getVarcharA(int col) {
         return getVarchar(col, 1);
     }
 
-    @Override @Nullable
+    @Override
+    @Nullable
     public Utf8Sequence getVarcharB(int col) {
         return getVarchar(col, 2);
     }

core/src/main/java/io/questdb/cairo/TableReaderSelectedColumnRecord.java

@@ -28,7 +28,6 @@
 import io.questdb.std.*;
 import io.questdb.std.str.CharSink;
 import io.questdb.std.str.Utf8Sequence;
-import io.questdb.std.str.DirectCharSequence;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 
@@ -102,19 +101,6 @@ public char getChar(int columnIndex) {
         return reader.getColumn(absoluteColumnIndex).getChar(offset);
     }
 
-    @Override
-    public DirectCharSequence getDirectStr(int columnIndex) {
-        final int col = deferenceColumn(columnIndex);
-        final long recordIndex = getAdjustedRecordIndex(col) * Long.BYTES;
-        final int absoluteColumnIndex = ifOffsetNegThen0ElseValue(
-                recordIndex,
-                TableReader.getPrimaryColumnIndex(columnBase, col)
-        );
-        long offset = reader.getColumn(absoluteColumnIndex + 1).getLong(recordIndex);
-        assert recordIndex != 0 || (offset == 0 || offset == Numbers.LONG_NaN);
-        return reader.getColumn(absoluteColumnIndex).getDirectStr(offset);
-    }
-
     @Override
     public double getDouble(int columnIndex) {
         final int col = deferenceColumn(columnIndex);

core/src/main/java/io/questdb/cairo/sql/Function.java

@@ -33,7 +33,6 @@
 import io.questdb.std.Long256;
 import io.questdb.std.ObjList;
 import io.questdb.std.str.CharSink;
-import io.questdb.std.str.DirectCharSequence;
 import io.questdb.std.str.Utf16Sink;
 import io.questdb.std.str.Utf8Sequence;
 import io.questdb.std.str.Utf8Sink;
@@ -91,18 +90,6 @@ default void close() {
 
     long getDate(Record rec);
 
-    /**
-     * Returns UTF-16 encoded off-heap string.
-     * <p>
-     * Must be called only if {@link #supportsDirectStr()} method returned true.
-     * The method is guaranteed to return off-heap strings with stable pointers,
-     * i.e. once a string is returned, its pointer remains actual until the end
-     * of query execution.
-     */
-    default DirectCharSequence getDirectStr(Record rec) {
-        throw new UnsupportedOperationException();
-    }
-
     double getDouble(Record rec);
 
     float getFloat(Record rec);
@@ -218,16 +205,6 @@ default boolean isUndefined() {
         return getType() == ColumnType.UNDEFINED;
     }
 
-    /**
-     * Returns true if {@link #getDirectStr(Record)} method can be safely called.
-     * The method is guaranteed to return off-heap strings with stable pointers,
-     * i.e. once a string is returned, its pointer remains actual until the end
-     * of query execution.
-     */
-    default boolean supportsDirectStr() {
-        return false;
-    }
-
     /**
      * Returns true if the function supports parallel execution, e.g. parallel filter
      * or GROUP BY. If the method returns false, single-threaded execution plan

core/src/main/java/io/questdb/cairo/sql/PageAddressCacheRecord.java

@@ -39,8 +39,8 @@
 public class PageAddressCacheRecord implements Record, Closeable {
 
     private final MemoryCR.ByteSequenceView bsview = new MemoryCR.ByteSequenceView();
-    private final DirectString csviewA = new DirectString();
-    private final DirectString csviewB = new DirectString();
+    private final StableDirectString csviewA = new StableDirectString();
+    private final StableDirectString csviewB = new StableDirectString();
     private final Long256Impl long256A = new Long256Impl();
     private final Long256Impl long256B = new Long256Impl();
     private final ObjList<SymbolTable> symbolTableCache = new ObjList<>();
@@ -119,18 +119,6 @@ public char getChar(int columnIndex) {
         return Unsafe.getUnsafe().getChar(address + (rowIndex << 1));
     }
 
-    @Override
-    public DirectCharSequence getDirectStr(int columnIndex) {
-        final long dataPageAddress = pageAddressCache.getPageAddress(frameIndex, columnIndex);
-        if (dataPageAddress == 0) {
-            return NullMemoryMR.INSTANCE.getDirectStr(0);
-        }
-        final long indexPageAddress = pageAddressCache.getIndexPageAddress(frameIndex, columnIndex);
-        final long offset = Unsafe.getUnsafe().getLong(indexPageAddress + (rowIndex << 3));
-        final long size = pageAddressCache.getPageSize(frameIndex, columnIndex);
-        return getStrA(dataPageAddress, offset, size, csviewA);
-    }
-
     @Override
     public double getDouble(int columnIndex) {
         final long address = pageAddressCache.getPageAddress(frameIndex, columnIndex);

core/src/main/java/io/questdb/cairo/sql/Record.java

@@ -26,7 +26,10 @@
 
 import io.questdb.std.BinarySequence;
 import io.questdb.std.Long256;
-import io.questdb.std.str.*;
+import io.questdb.std.str.CharSink;
+import io.questdb.std.str.Utf16Sink;
+import io.questdb.std.str.Utf8Sequence;
+import io.questdb.std.str.Utf8Sink;
 import org.jetbrains.annotations.Nullable;
 
 /**
@@ -102,15 +105,6 @@ default long getDate(int col) {
         return getLong(col);
     }
 
-    /**
-     * Gets the off-heap (direct) value of a string column by index
-     *
-     * @param col numeric index of the column
-     * @return direct string, null if string is empty
-     */
-    default DirectCharSequence getDirectStr(int col) {
-        throw new UnsupportedOperationException();
-    }
 
     /**
      * Gets the value of a double column by index

core/src/main/java/io/questdb/cairo/vm/AbstractMemoryCR.java

@@ -34,8 +34,8 @@
 public abstract class AbstractMemoryCR implements MemoryCR, Mutable {
 
     private final MemoryCR.ByteSequenceView bsview = new MemoryCR.ByteSequenceView();
-    private final DirectString csviewA = new DirectString();
-    private final DirectString csviewB = new DirectString();
+    private final DirectString csviewA;
+    private final DirectString csviewB;
     private final Long256Impl long256A = new Long256Impl();
     private final Long256Impl long256B = new Long256Impl();
     private final Utf8SplitString utf8SplitViewA = new Utf8SplitString();
@@ -48,6 +48,16 @@ public abstract class AbstractMemoryCR implements MemoryCR, Mutable {
     protected long size = 0;
     private long shiftAddressRight = 0;
 
+    public AbstractMemoryCR(boolean stableStrings) {
+        if (stableStrings) {
+            csviewA = new StableDirectString();
+            csviewB = new StableDirectString();
+        } else {
+            csviewA = new DirectString();
+            csviewB = new DirectString();
+        }
+    }
+
     public long addressOf(long offset) {
         offset -= shiftAddressRight;
         assert offset <= size : "offset=" + offset + ", size=" + size;
@@ -112,12 +122,14 @@ public final CharSequence getStrB(long offset) {
         return getStr(offset, csviewB);
     }
 
-    @Override @NotNull
+    @Override
+    @NotNull
     public Utf8Sequence getVarcharA(long offset, int size, boolean ascii) {
         return getVarchar(offset, size, utf8viewA, ascii);
     }
 
-    @Override @NotNull
+    @Override
+    @NotNull
     public Utf8Sequence getVarcharB(long offset, int size, boolean ascii) {
         return getVarchar(offset, size, utf8viewB, ascii);
     }