ESQL: Reserve memory TopN (elastic#134235) (elastic#134335)

* ESQL: Reserve memory TopN (elastic#134235)

Tracks the more memory that's involved in topn.

Lucene doesn't track memory usage for TopN and can use a fair bit of it.
Try this query:
```
FROM big_table
| SORT a, b, c, d, e
| LIMIT 1000000
| STATS MAX(a)
```

We attempt to return all million documents from lucene. Is we did this
with the compute engine we're track all of the memory usage. With lucene
we have to reserve it.

In the case of the query above the sort keys weight 8 bytes each. 40
bytes total. Plus another 72 for Lucene's `FieldDoc`. And another 40 at
least for copying to the values to `FieldDoc`. That totals something
like 152 bytes a piece. That's 145mb. Worth tracking!

 ## Esql Engine TopN

Esql *does* track memory for topn, but it doesn't track the memory used by the min heap itself. It's just a big array of pointers. But it can get very big!

* fix backport

Author: nik9000

docs/changelog/134235.yaml

@@ -0,0 +1,5 @@
+pr: 134235
+summary: Reserve memory for Lucene's TopN
+area: ES|QL
+type: bug
+issues: []

test/external-modules/esql-heap-attack/src/javaRestTest/java/org/elasticsearch/xpack/esql/heap_attack/HeapAttackIT.java

@@ -88,7 +88,7 @@ public void skipOnAborted() {
      * This used to fail, but we've since compacted top n so it actually succeeds now.
      */
     public void testSortByManyLongsSuccess() throws IOException {
-        initManyLongs();
+        initManyLongs(10);
         Map<String, Object> response = sortByManyLongs(500);
         ListMatcher columns = matchesList().item(matchesMap().entry("name", "a").entry("type", "long"))
             .item(matchesMap().entry("name", "b").entry("type", "long"));
@@ -105,7 +105,7 @@ public void testSortByManyLongsSuccess() throws IOException {
      * This used to crash the node with an out of memory, but now it just trips a circuit breaker.
      */
     public void testSortByManyLongsTooMuchMemory() throws IOException {
-        initManyLongs();
+        initManyLongs(10);
         // 5000 is plenty to break on most nodes
         assertCircuitBreaks(attempt -> sortByManyLongs(attempt * 5000));
     }
@@ -114,7 +114,7 @@ public void testSortByManyLongsTooMuchMemory() throws IOException {
      * This should record an async response with a {@link CircuitBreakingException}.
      */
     public void testSortByManyLongsTooMuchMemoryAsync() throws IOException {
-        initManyLongs();
+        initManyLongs(10);
         Request request = new Request("POST", "/_query/async");
         request.addParameter("error_trace", "");
         request.setJsonEntity(makeSortByManyLongs(5000).toString().replace("\n", "\\n"));
@@ -191,6 +191,22 @@ public void testSortByManyLongsTooMuchMemoryAsync() throws IOException {
         );
     }
 
+    public void testSortByManyLongsGiantTopN() throws IOException {
+        initManyLongs(10);
+        assertMap(
+            sortBySomeLongsLimit(100000),
+            matchesMap().entry("took", greaterThan(0))
+                .entry("is_partial", false)
+                .entry("columns", List.of(Map.of("name", "MAX(a)", "type", "long")))
+                .entry("values", List.of(List.of(9)))
+        );
+    }
+
+    public void testStupidTopN() throws IOException {
+        initManyLongs(1); // Doesn't actually matter how much data there is.
+        assertCircuitBreaks(attempt -> sortBySomeLongsLimit(2147483630));
+    }
+
     private static final int MAX_ATTEMPTS = 5;
 
     interface TryCircuitBreaking {
@@ -249,11 +265,25 @@ private StringBuilder makeSortByManyLongs(int count) {
         return query;
     }
 
+    private Map<String, Object> sortBySomeLongsLimit(int count) throws IOException {
+        logger.info("sorting by 5 longs, keeping {}", count);
+        return responseAsMap(query(makeSortBySomeLongsLimit(count), null));
+    }
+
+    private String makeSortBySomeLongsLimit(int count) {
+        StringBuilder query = new StringBuilder("{\"query\": \"FROM manylongs\n");
+        query.append("| SORT a, b, c, d, e\n");
+        query.append("| LIMIT ").append(count).append("\n");
+        query.append("| STATS MAX(a)\n");
+        query.append("\"}");
+        return query.toString();
+    }
+
     /**
      * This groups on about 200 columns which is a lot but has never caused us trouble.
      */
     public void testGroupOnSomeLongs() throws IOException {
-        initManyLongs();
+        initManyLongs(10);
         Response resp = groupOnManyLongs(200);
         Map<String, Object> map = responseAsMap(resp);
         ListMatcher columns = matchesList().item(matchesMap().entry("name", "MAX(a)").entry("type", "long"));
@@ -265,7 +295,7 @@ public void testGroupOnSomeLongs() throws IOException {
      * This groups on 5000 columns which used to throw a {@link StackOverflowError}.
      */
     public void testGroupOnManyLongs() throws IOException {
-        initManyLongs();
+        initManyLongs(10);
         Response resp = groupOnManyLongs(5000);
         Map<String, Object> map = responseAsMap(resp);
         ListMatcher columns = matchesList().item(matchesMap().entry("name", "MAX(a)").entry("type", "long"));
@@ -333,15 +363,15 @@ private Response concat(int evals) throws IOException {
      */
     public void testManyConcat() throws IOException {
         int strings = 300;
-        initManyLongs();
+        initManyLongs(10);
         assertManyStrings(manyConcat("FROM manylongs", strings), strings);
     }
 
     /**
      * Hits a circuit breaker by building many moderately long strings.
      */
     public void testHugeManyConcat() throws IOException {
-        initManyLongs();
+        initManyLongs(10);
         // 2000 is plenty to break on most nodes
         assertCircuitBreaks(attempt -> manyConcat("FROM manylongs", attempt * 2000));
     }
@@ -412,15 +442,15 @@ private Map<String, Object> manyConcat(String init, int strings) throws IOExcept
      */
     public void testManyRepeat() throws IOException {
         int strings = 30;
-        initManyLongs();
+        initManyLongs(10);
         assertManyStrings(manyRepeat("FROM manylongs", strings), 30);
     }
 
     /**
      * Hits a circuit breaker by building many moderately long strings.
      */
     public void testHugeManyRepeat() throws IOException {
-        initManyLongs();
+        initManyLongs(10);
         // 75 is plenty to break on most nodes
         assertCircuitBreaks(attempt -> manyRepeat("FROM manylongs", attempt * 75));
     }
@@ -478,7 +508,7 @@ private void assertManyStrings(Map<String, Object> resp, int strings) throws IOE
     }
 
     public void testManyEval() throws IOException {
-        initManyLongs();
+        initManyLongs(10);
         Map<String, Object> response = manyEval(1);
         ListMatcher columns = matchesList();
         columns = columns.item(matchesMap().entry("name", "a").entry("type", "long"));
@@ -493,7 +523,7 @@ public void testManyEval() throws IOException {
     }
 
     public void testTooManyEval() throws IOException {
-        initManyLongs();
+        initManyLongs(10);
         // 490 is plenty to fail on most nodes
         assertCircuitBreaks(attempt -> manyEval(attempt * 490));
     }
@@ -756,24 +786,34 @@ private Map<String, Object> enrichExplosion(int sensorDataCount, int lookupEntri
         }
     }
 
-    private void initManyLongs() throws IOException {
+    private void initManyLongs(int countPerLong) throws IOException {
         logger.info("loading many documents with longs");
         StringBuilder bulk = new StringBuilder();
-        for (int a = 0; a < 10; a++) {
-            for (int b = 0; b < 10; b++) {
-                for (int c = 0; c < 10; c++) {
-                    for (int d = 0; d < 10; d++) {
-                        for (int e = 0; e < 10; e++) {
+        int flush = 0;
+        for (int a = 0; a < countPerLong; a++) {
+            for (int b = 0; b < countPerLong; b++) {
+                for (int c = 0; c < countPerLong; c++) {
+                    for (int d = 0; d < countPerLong; d++) {
+                        for (int e = 0; e < countPerLong; e++) {
                             bulk.append(String.format(Locale.ROOT, """
                                 {"create":{}}
                                 {"a":%d,"b":%d,"c":%d,"d":%d,"e":%d}
                                 """, a, b, c, d, e));
+                            flush++;
+                            if (flush % 10_000 == 0) {
+                                bulk("manylongs", bulk.toString());
+                                bulk.setLength(0);
+                                logger.info(
+                                    "flushing {}/{} to manylongs",
+                                    flush,
+                                    countPerLong * countPerLong * countPerLong * countPerLong * countPerLong
+                                );
+
+                            }
                         }
                     }
                 }
             }
-            bulk("manylongs", bulk.toString());
-            bulk.setLength(0);
         }
         initIndex("manylongs", bulk.toString());
     }