gh-135953: Reduce memory usage of stack collectors (#138875)

The stack collector base class keeps all frames until export() is
called, which causes significant unnecessary memory usage. Instead, we
can process the frames on the fly in the collect call by dispatching the
aggregation logic to the subclass through the process_frames method.

Co-authored-by: Pablo Galindo Salgado <[email protected]>

Author: lkollar

Lib/profiling/sampling/__init__.py

@@ -7,5 +7,6 @@
 from .collector import Collector
 from .pstats_collector import PstatsCollector
 from .stack_collector import CollapsedStackCollector
+from .string_table import StringTable
 
-__all__ = ("Collector", "PstatsCollector", "CollapsedStackCollector")
+__all__ = ("Collector", "PstatsCollector", "CollapsedStackCollector", "StringTable")

Lib/profiling/sampling/flamegraph.js

@@ -1,5 +1,50 @@
 const EMBEDDED_DATA = {{FLAMEGRAPH_DATA}};
 
+// Global string table for resolving string indices
+let stringTable = [];
+
+// Function to resolve string indices to actual strings
+function resolveString(index) {
+    if (typeof index === 'number' && index >= 0 && index < stringTable.length) {
+        return stringTable[index];
+    }
+    // Fallback for non-indexed strings or invalid indices
+    return String(index);
+}
+
+// Function to recursively resolve all string indices in flamegraph data
+function resolveStringIndices(node) {
+    if (!node) return node;
+
+    // Create a copy to avoid mutating the original
+    const resolved = { ...node };
+
+    // Resolve string fields
+    if (typeof resolved.name === 'number') {
+        resolved.name = resolveString(resolved.name);
+    }
+    if (typeof resolved.filename === 'number') {
+        resolved.filename = resolveString(resolved.filename);
+    }
+    if (typeof resolved.funcname === 'number') {
+        resolved.funcname = resolveString(resolved.funcname);
+    }
+
+    // Resolve source lines if present
+    if (Array.isArray(resolved.source)) {
+        resolved.source = resolved.source.map(index =>
+            typeof index === 'number' ? resolveString(index) : index
+        );
+    }
+
+    // Recursively resolve children
+    if (Array.isArray(resolved.children)) {
+        resolved.children = resolved.children.map(child => resolveStringIndices(child));
+    }
+
+    return resolved;
+}
+
 // Python color palette - cold to hot
 const pythonColors = [
   "#fff4bf", // Coldest - light yellow (<1%)
@@ -100,6 +145,10 @@ function createPythonTooltip(data) {
         </div>`;
     }
 
+    // Resolve strings for display
+    const funcname = resolveString(d.data.funcname) || resolveString(d.data.name);
+    const filename = resolveString(d.data.filename) || "";
+
     const tooltipHTML = `
       <div>
         <div style="color: #3776ab; font-weight: 600; font-size: 16px;
@@ -257,9 +306,9 @@ function updateSearchHighlight(searchTerm, searchInput) {
     let matchCount = 0;
     d3.selectAll("#chart rect").each(function (d) {
       if (d && d.data) {
-        const name = d.data.name || "";
-        const funcname = d.data.funcname || "";
-        const filename = d.data.filename || "";
+        const name = resolveString(d.data.name) || "";
+        const funcname = resolveString(d.data.funcname) || "";
+        const filename = resolveString(d.data.filename) || "";
         const term = searchTerm.toLowerCase();
         const matches =
           name.toLowerCase().includes(term) ||
@@ -317,12 +366,20 @@ function handleResize(chart, data) {
 
 function initFlamegraph() {
   ensureLibraryLoaded();
-  const tooltip = createPythonTooltip(EMBEDDED_DATA);
-  const chart = createFlamegraph(tooltip, EMBEDDED_DATA.value);
-  renderFlamegraph(chart, EMBEDDED_DATA);
+
+  // Extract string table if present and resolve string indices
+  let processedData = EMBEDDED_DATA;
+  if (EMBEDDED_DATA.strings) {
+    stringTable = EMBEDDED_DATA.strings;
+    processedData = resolveStringIndices(EMBEDDED_DATA);
+  }
+
+  const tooltip = createPythonTooltip(processedData);
+  const chart = createFlamegraph(tooltip, processedData.value);
+  renderFlamegraph(chart, processedData);
   attachPanelControls();
   initSearchHandlers();
-  handleResize(chart, EMBEDDED_DATA);
+  handleResize(chart, processedData);
 }
 
 if (document.readyState === "loading") {
@@ -338,7 +395,10 @@ function populateStats(data) {
   const functionMap = new Map();
 
   function collectFunctions(node) {
-    if (node.filename && node.funcname) {
+    const filename = resolveString(node.filename);
+    const funcname = resolveString(node.funcname);
+
+    if (filename && funcname) {
       // Calculate direct samples (this node's value minus children's values)
       let childrenValue = 0;
       if (node.children) {
@@ -347,23 +407,23 @@ function populateStats(data) {
       const directSamples = Math.max(0, node.value - childrenValue);
 
       // Use file:line:funcname as key to ensure uniqueness
-      const funcKey = `${node.filename}:${node.lineno || '?'}:${node.funcname}`;
+      const funcKey = `${filename}:${node.lineno || '?'}:${funcname}`;
 
       if (functionMap.has(funcKey)) {
         const existing = functionMap.get(funcKey);
         existing.directSamples += directSamples;
         existing.directPercent = (existing.directSamples / totalSamples) * 100;
         // Keep the most representative file/line (the one with more samples)
         if (directSamples > existing.maxSingleSamples) {
-          existing.filename = node.filename;
+          existing.filename = filename;
           existing.lineno = node.lineno || '?';
           existing.maxSingleSamples = directSamples;
         }
       } else {
         functionMap.set(funcKey, {
-          filename: node.filename,
+          filename: filename,
           lineno: node.lineno || '?',
-          funcname: node.funcname,
+          funcname: funcname,
           directSamples,
           directPercent: (directSamples / totalSamples) * 100,
           maxSingleSamples: directSamples