Remove redundant toString() in string/symbol columns

Pass CharSequence directly through the symbol and string column
paths instead of eagerly converting to String.

In stringColumn(), addString() already copies character data
immediately via putUtf8(), so the toString() was pure waste.

In the symbol path, propagate CharSequence through
getOrAddGlobalSymbol() and addSymbolWithGlobalId() down to the
dictionary lookup. GlobalSymbolDictionary.getOrAddSymbol() now
accepts CharSequence and only calls toString() when a symbol is
new and must be stored. CharSequenceIntHashMap.get() already
accepts CharSequence for lookups, so repeated symbols incur
zero allocation.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: mtopolnik

core/src/main/java/io/questdb/client/cutlass/qwp/client/GlobalSymbolDictionary.java

@@ -94,7 +94,7 @@ public int getId(String symbol) {
      * @return the global ID for this symbol (>= 0)
      * @throws IllegalArgumentException if symbol is null
      */
-    public int getOrAddSymbol(String symbol) {
+    public int getOrAddSymbol(CharSequence symbol) {
         if (symbol == null) {
             throw new IllegalArgumentException("symbol cannot be null");
         }
@@ -104,10 +104,11 @@ public int getOrAddSymbol(String symbol) {
             return existingId;
         }
 
-        // Assign new ID
+        // Assign new ID — toString() only for new symbols that must be stored
+        String symbolStr = symbol.toString();
         int newId = idToSymbol.size();
-        symbolToId.put(symbol, newId);
-        idToSymbol.add(symbol);
+        symbolToId.put(symbolStr, newId);
+        idToSymbol.add(symbolStr);
         return newId;
     }
 

core/src/main/java/io/questdb/client/cutlass/qwp/client/QwpWebSocketSender.java

@@ -636,7 +636,7 @@ public int getMaxSentSymbolId() {
      * @param symbol the symbol value to register
      * @return the global symbol ID
      */
-    public int getOrAddGlobalSymbol(String symbol) {
+    public int getOrAddGlobalSymbol(CharSequence symbol) {
         int globalId = globalSymbolDictionary.getOrAddSymbol(symbol);
         if (globalId > currentBatchMaxSymbolId) {
             currentBatchMaxSymbolId = globalId;
@@ -801,7 +801,7 @@ public QwpWebSocketSender stringColumn(CharSequence columnName, CharSequence val
         checkNotClosed();
         checkTableSelected();
         QwpTableBuffer.ColumnBuffer col = currentTableBuffer.getOrCreateColumn(checkedColumnName(columnName), TYPE_STRING, true);
-        col.addString(value != null ? value.toString() : null);
+        col.addString(value);
         return this;
     }
 

core/src/main/java/io/questdb/client/cutlass/qwp/protocol/QwpTableBuffer.java

@@ -78,7 +78,7 @@ public QwpTableBuffer(String tableName) {
     /**
      * Use this constructor overload to allow writing to a symbol column.
      * {@link ColumnBuffer#addSymbol(CharSequence)} needs the sender to
-     * call {@link QwpWebSocketSender#getOrAddGlobalSymbol(String)}, registering
+     * call {@link QwpWebSocketSender#getOrAddGlobalSymbol(CharSequence)}, registering
      * the symbol in the global dictionary shared with the server.
      */
     public QwpTableBuffer(String tableName, QwpWebSocketSender sender) {
@@ -1063,9 +1063,8 @@ public void addSymbol(CharSequence value) {
                 return;
             }
             if (sender != null) {
-                String symbolValue = value.toString();
-                int globalId = sender.getOrAddGlobalSymbol(symbolValue);
-                addSymbolWithGlobalId(symbolValue, globalId);
+                int globalId = sender.getOrAddGlobalSymbol(value);
+                addSymbolWithGlobalId(value, globalId);
                 return;
             }
             ensureNullBitmapCapacity();
@@ -1092,9 +1091,8 @@ public void addSymbolUtf8(long ptr, int len) {
                 throw new AssertionError("unreachable");
             }
             if (sender != null) {
-                String symbolValue = lookupSink.toString();
-                int globalId = sender.getOrAddGlobalSymbol(symbolValue);
-                addSymbolWithGlobalId(symbolValue, globalId);
+                int globalId = sender.getOrAddGlobalSymbol(lookupSink);
+                addSymbolWithGlobalId(lookupSink, globalId);
                 return;
             }
             ensureNullBitmapCapacity();
@@ -1104,7 +1102,7 @@ public void addSymbolUtf8(long ptr, int len) {
             size++;
         }
 
-        public void addSymbolWithGlobalId(String value, int globalId) {
+        public void addSymbolWithGlobalId(CharSequence value, int globalId) {
             if (value == null) {
                 addNull();
                 return;