Scripting: Context script cache unlimited compile (#53769)

* Adds "unlimited" compilation rate for context script caches
* `script.context.${CONTEXT}.max_compilations_rate` = `unlimited`
  disables compilation rate limiting for `${CONTEXT}`'s script
  cache

Refs: #50152

Author: stu-elastic

server/src/main/java/org/elasticsearch/script/ScriptCache.java

@@ -40,14 +40,16 @@ public class ScriptCache {
 
     private static final Logger logger = LogManager.getLogger(ScriptService.class);
 
+    static final Tuple<Integer, TimeValue> UNLIMITED_COMPILATION_RATE = new Tuple<>(0, TimeValue.ZERO);
+
     private final Cache<CacheKey, Object> cache;
     private final ScriptMetrics scriptMetrics;
 
     private final Object lock = new Object();
 
-    // Mutable fields
-    private long lastInlineCompileTime;
-    private double scriptsPerTimeWindow;
+    // Mutable fields, visible for tests
+    long lastInlineCompileTime;
+    double scriptsPerTimeWindow;
 
     // Cache settings or derived from settings
     final int cacheSize;
@@ -150,8 +152,7 @@ public ScriptStats stats() {
      * is discarded - there can never be more water in the bucket than the size of the bucket.
      */
     void checkCompilationLimit() {
-        if (rate.v1() == 0 && rate.v2().getNanos() == 0) {
-            // unlimited
+        if (rate.equals(UNLIMITED_COMPILATION_RATE)) {
             return;
         }
 

server/src/main/java/org/elasticsearch/script/ScriptService.java

@@ -128,10 +128,16 @@ public class ScriptService implements Closeable, ClusterStateApplier {
             key -> Setting.positiveTimeSetting(key, SCRIPT_GENERAL_CACHE_EXPIRE_SETTING, TimeValue.timeValueMillis(0),
                                                Property.NodeScope, Property.Dynamic));
 
+    // Unlimited compilation rate for context-specific script caches
+    static final String UNLIMITED_COMPILATION_RATE_KEY = "unlimited";
+
     public static final Setting.AffixSetting<Tuple<Integer, TimeValue>> SCRIPT_MAX_COMPILATIONS_RATE_SETTING =
         Setting.affixKeySetting(CONTEXT_PREFIX,
             "max_compilations_rate",
-            key -> new Setting<>(key, "75/5m", MAX_COMPILATION_RATE_FUNCTION, Property.NodeScope, Property.Dynamic));
+            key -> new Setting<>(key, "75/5m",
+                (String value) -> value.equals(UNLIMITED_COMPILATION_RATE_KEY) ? ScriptCache.UNLIMITED_COMPILATION_RATE:
+                                                                                 MAX_COMPILATION_RATE_FUNCTION.apply(value),
+                Property.NodeScope, Property.Dynamic));
 
     private static final Tuple<Integer, TimeValue> SCRIPT_COMPILATION_RATE_ZERO = new Tuple<>(0, TimeValue.ZERO);
 

server/src/test/java/org/elasticsearch/script/ScriptCacheTests.java

@@ -52,4 +52,17 @@ public void testCompilationCircuitBreaking() throws Exception {
             cache.checkCompilationLimit();
         }
     }
+
+    public void testUnlimitedCompilationRate() {
+        final Integer size = ScriptService.SCRIPT_GENERAL_CACHE_SIZE_SETTING.get(Settings.EMPTY);
+        final TimeValue expire = ScriptService.SCRIPT_GENERAL_CACHE_EXPIRE_SETTING.get(Settings.EMPTY);
+        ScriptCache cache = new ScriptCache(size, expire, ScriptCache.UNLIMITED_COMPILATION_RATE);
+        long lastInlineCompileTime = cache.lastInlineCompileTime;
+        double scriptsPerTimeWindow = cache.scriptsPerTimeWindow;
+        for(int i=0; i < 3000; i++) {
+            cache.checkCompilationLimit();
+            assertEquals(lastInlineCompileTime, cache.lastInlineCompileTime);
+            assertEquals(scriptsPerTimeWindow, cache.scriptsPerTimeWindow, 0.0); // delta of 0.0 because it should never change
+        }
+    }
 }

server/src/test/java/org/elasticsearch/script/ScriptServiceTests.java

@@ -450,6 +450,24 @@ public void testCacheHolderContextConstructor() {
         assertEquals(zero, holder.contextCache.get("baz").get().rate);
     }
 
+    public void testCompilationRateUnlimitedContextOnly() throws IOException {
+        IllegalArgumentException illegal = expectThrows(IllegalArgumentException.class, () -> {
+            buildScriptService(Settings.builder()
+                .put(SCRIPT_GENERAL_MAX_COMPILATIONS_RATE_SETTING.getKey(), ScriptService.UNLIMITED_COMPILATION_RATE_KEY)
+                .build());
+        });
+        assertEquals("parameter must contain a positive integer and a timevalue, i.e. 10/1m, but was [unlimited]", illegal.getMessage());
+
+        // Should not throw.
+        buildScriptService(Settings.builder()
+            .put(SCRIPT_MAX_COMPILATIONS_RATE_SETTING.getConcreteSettingForNamespace("ingest").getKey(),
+                 ScriptService.UNLIMITED_COMPILATION_RATE_KEY)
+            .put(SCRIPT_MAX_COMPILATIONS_RATE_SETTING.getConcreteSettingForNamespace("field").getKey(),
+                 ScriptService.UNLIMITED_COMPILATION_RATE_KEY)
+            .put(SCRIPT_GENERAL_MAX_COMPILATIONS_RATE_SETTING.getKey(), ScriptService.USE_CONTEXT_RATE_KEY)
+            .build());
+    }
+
     public void testCacheHolderChangeSettings() {
         String fooCompilationRate = "77/5m";
         String barCompilationRate = "78/6m";
@@ -459,7 +477,7 @@ public void testCacheHolderChangeSettings() {
         Settings s = Settings.builder()
             .put(SCRIPT_GENERAL_MAX_COMPILATIONS_RATE_SETTING.getKey(), compilationRate)
             .build();
-        Set<String> contexts = Set.of("foo", "bar", "baz");
+        Set<String> contexts = Set.of("foo", "bar", "baz", "qux");
         ScriptService.CacheHolder holder = new ScriptService.CacheHolder(s, contexts, true);
 
         assertNotNull(holder.general);
@@ -470,16 +488,19 @@ public void testCacheHolderChangeSettings() {
             .put(SCRIPT_GENERAL_MAX_COMPILATIONS_RATE_SETTING.getKey(), ScriptService.USE_CONTEXT_RATE_KEY)
             .put(SCRIPT_MAX_COMPILATIONS_RATE_SETTING.getConcreteSettingForNamespace("foo").getKey(), fooCompilationRate)
             .put(SCRIPT_MAX_COMPILATIONS_RATE_SETTING.getConcreteSettingForNamespace("bar").getKey(), barCompilationRate)
+            .put(SCRIPT_MAX_COMPILATIONS_RATE_SETTING.getConcreteSettingForNamespace("qux").getKey(),
+                 ScriptService.UNLIMITED_COMPILATION_RATE_KEY)
             .build()
         );
 
         assertNull(holder.general);
         assertNotNull(holder.contextCache);
-        assertEquals(3, holder.contextCache.size());
+        assertEquals(4, holder.contextCache.size());
         assertEquals(contexts, holder.contextCache.keySet());
 
         assertEquals(ScriptService.MAX_COMPILATION_RATE_FUNCTION.apply(fooCompilationRate), holder.contextCache.get("foo").get().rate);
         assertEquals(ScriptService.MAX_COMPILATION_RATE_FUNCTION.apply(barCompilationRate), holder.contextCache.get("bar").get().rate);
+        assertEquals(ScriptCache.UNLIMITED_COMPILATION_RATE, holder.contextCache.get("qux").get().rate);
         assertEquals(ScriptService.SCRIPT_MAX_COMPILATIONS_RATE_SETTING.getDefault(Settings.EMPTY),
             holder.contextCache.get("baz").get().rate);