Add a cluster setting to disallow slow queries

Add a new cluster setting `search.disallow_slow_queries` which by
default is `false`. If set to `true` then certain queries (prefix,
fuzzy, regexp and wildcard) that have usually slow performance cannot
be executed and an exception is thrown.

Closes: elastic#29050

docs/reference/query-dsl.asciidoc

@@ -25,6 +25,14 @@ or to alter their behaviour (such as the
 
 Query clauses behave differently depending on whether they are used in
 <<query-filter-context,query context or filter context>>.
+
+[[query-dsl-disallow-slow]]
+== Disallow slow queries
+Certain queries like <<query-dsl-fuzzy-query,`fuzzy`>>, <<query-dsl-prefix-query,`prefix`>>,
+<<query-dsl-regexp-query,`regexp`>> and <<query-dsl-bool-query,`wildcard`>> ,
+that are usually slow performance can affect the cluster performance.
+The execution of such queries can be prevented by setting the value of the `search.disallow_slow_queries`
+setting to `true` (defaults tp `false`).
 --
 
 include::query-dsl/query_filter_context.asciidoc[]
@@ -51,4 +59,4 @@ include::query-dsl/minimum-should-match.asciidoc[]
 
 include::query-dsl/multi-term-rewrite.asciidoc[]
 
-include::query-dsl/regexp-syntax.asciidoc[]
+include::query-dsl/regexp-syntax.asciidoc[]

docs/reference/query-dsl/fuzzy-query.asciidoc

@@ -97,4 +97,8 @@ adjacent characters (ab → ba). Defaults to `true`.
 
 `rewrite`::
 (Optional, string) Method used to rewrite the query. For valid values and more
-information, see the <<query-dsl-multi-term-rewrite, `rewrite` parameter>>.
+information, see the <<query-dsl-multi-term-rewrite, `rewrite` parameter>>.
+
+==== Notes
+Fuzzy queries will not be executed if <<query-dsl-disallow-slow, `search.disallow_slow_queries`>>
+is set to true.

docs/reference/query-dsl/prefix-query.asciidoc

@@ -64,4 +64,12 @@ GET /_search
 You can speed up prefix queries using the <<index-prefixes,`index_prefixes`>>
 mapping parameter. If enabled, {es} indexes prefixes between 2 and 5
 characters in a separate field. This lets {es} run prefix queries more
-efficiently at the cost of a larger index.
+efficiently at the cost of a larger index.
+
+[[prefix-query-disallow-slow]]
+===== Disallow slow queries
+Prefix queries will not be executed if <<query-dsl-disallow-slow, `search.disallow_slow_queries`>>
+is set to true. If <<index-prefixes, `index prefixes`>> are enabled though, an optimised query is
+built, which is not considered slow and is executed despite of the fact that the
+<<query-dsl-disallow-slow, `search.disallow_slow_queries`>> set to true.
+

docs/reference/query-dsl/query-string-query.asciidoc

@@ -537,3 +537,9 @@ The example above creates a boolean query:
 `(blended(terms:[field2:this, field1:this]) blended(terms:[field2:that, field1:that]) blended(terms:[field2:thus, field1:thus]))~2`
 
 that matches documents with at least two of the three per-term blended queries.
+
+==== Notes
+===== Disallow slow queries
+Query string query can be internally be transformed to a <<query-dsl-prefix-query, `prefix query`>> which means
+that if the prefix queries are disabled as explained <<prefix-query-disallow-slow, here>> the query will not be
+executed and an exception will be thrown.

docs/reference/query-dsl/regexp-query.asciidoc

@@ -86,3 +86,8 @@ regular expressions.
 `rewrite`::
 (Optional, string) Method used to rewrite the query. For valid values and more
 information, see the <<query-dsl-multi-term-rewrite, `rewrite` parameter>>.
+
+==== Notes
+===== Disallow slow queries
+Regexp queries will not be executed if <<query-dsl-disallow-slow, `search.disallow_slow_queries`>>
+is set to true.

docs/reference/query-dsl/wildcard-query.asciidoc

@@ -67,4 +67,9 @@ increases the relevance score.
 
 `rewrite`::
 (Optional, string) Method used to rewrite the query. For valid values and more information, see the
-<<query-dsl-multi-term-rewrite, `rewrite` parameter>>.
+<<query-dsl-multi-term-rewrite, `rewrite` parameter>>.
+
+==== Notes
+===== Disallow slow queries
+Wildcard queries will not be executed if <<query-dsl-disallow-slow, `search.disallow_slow_queries`>>
+is set to true.

modules/mapper-extras/src/test/java/org/elasticsearch/index/mapper/SearchAsYouTypeFieldTypeTests.java

@@ -26,6 +26,7 @@
 import org.apache.lucene.search.TermInSetQuery;
 import org.apache.lucene.search.TermQuery;
 import org.apache.lucene.util.BytesRef;
+import org.elasticsearch.ElasticsearchException;
 import org.elasticsearch.index.mapper.SearchAsYouTypeFieldMapper.Defaults;
 import org.elasticsearch.index.mapper.SearchAsYouTypeFieldMapper.PrefixFieldType;
 import org.elasticsearch.index.mapper.SearchAsYouTypeFieldMapper.SearchAsYouTypeFieldType;
@@ -100,14 +101,19 @@ public void testPrefixQuery() {
 
         // this term should be a length that can be rewriteable to a term query on the prefix field
         final String withinBoundsTerm = "foo";
-        assertThat(fieldType.prefixQuery(withinBoundsTerm, CONSTANT_SCORE_REWRITE, null),
+        assertThat(fieldType.prefixQuery(withinBoundsTerm, CONSTANT_SCORE_REWRITE, randomMockShardContext()),
             equalTo(new ConstantScoreQuery(new TermQuery(new Term(PREFIX_NAME, withinBoundsTerm)))));
 
         // our defaults don't allow a situation where a term can be too small
 
         // this term should be too long to be rewriteable to a term query on the prefix field
         final String longTerm = "toolongforourprefixfieldthistermis";
-        assertThat(fieldType.prefixQuery(longTerm, CONSTANT_SCORE_REWRITE, null),
+        assertThat(fieldType.prefixQuery(longTerm, CONSTANT_SCORE_REWRITE, MOCK_QSC),
             equalTo(new PrefixQuery(new Term(NAME, longTerm))));
+
+        ElasticsearchException ee = expectThrows(ElasticsearchException.class,
+                () -> fieldType.prefixQuery(longTerm, CONSTANT_SCORE_REWRITE, MOCK_QSC_DISALLOW_SLOW));
+        assertEquals("prefix queries cannot be executed when 'search.disallow_slow_queries' is set to true",
+                ee.getMessage());
     }
 }

plugins/analysis-icu/src/main/java/org/elasticsearch/index/mapper/ICUCollationKeywordFieldMapper.java

@@ -158,7 +158,7 @@ protected BytesRef indexedValueForSearch(Object value) {
 
         @Override
         public Query fuzzyQuery(Object value, Fuzziness fuzziness, int prefixLength, int maxExpansions,
-                                boolean transpositions) {
+                                boolean transpositions, QueryShardContext context) {
             throw new UnsupportedOperationException("[fuzzy] queries are not supported on [" + CONTENT_TYPE + "] fields.");
         }
 

plugins/analysis-icu/src/test/java/org/elasticsearch/index/mapper/CollationFieldTypeTests.java

@@ -102,31 +102,31 @@ public void testRegexpQuery() {
         ft.setName("field");
         ft.setIndexOptions(IndexOptions.DOCS);
         expectThrows(UnsupportedOperationException.class,
-            () -> ft.regexpQuery("foo.*", 0, 10, null, null));
+            () -> ft.regexpQuery("foo.*", 0, 10, null, randomMockShardContext()));
     }
 
     public void testFuzzyQuery() {
         MappedFieldType ft = createDefaultFieldType();
         ft.setName("field");
         ft.setIndexOptions(IndexOptions.DOCS);
         expectThrows(UnsupportedOperationException.class,
-            () -> ft.fuzzyQuery("foo", Fuzziness.fromEdits(2), 1, 50, true));
+            () -> ft.fuzzyQuery("foo", Fuzziness.fromEdits(2), 1, 50, true, randomMockShardContext()));
     }
 
     public void testPrefixQuery() {
         MappedFieldType ft = createDefaultFieldType();
         ft.setName("field");
         ft.setIndexOptions(IndexOptions.DOCS);
         expectThrows(UnsupportedOperationException.class,
-            () -> ft.prefixQuery("prefix", null, null));
+            () -> ft.prefixQuery("prefix", null, randomMockShardContext()));
     }
 
     public void testWildcardQuery() {
         MappedFieldType ft = createDefaultFieldType();
         ft.setName("field");
         ft.setIndexOptions(IndexOptions.DOCS);
         expectThrows(UnsupportedOperationException.class,
-            () -> ft.wildcardQuery("foo*", null, null));
+            () -> ft.wildcardQuery("foo*", null, randomMockShardContext()));
     }
 
     public void testRangeQuery() {

rest-api-spec/src/main/resources/rest-api-spec/test/search/320_disallow_queries.yml

@@ -0,0 +1,213 @@
+---
+setup:
+  - skip:
+      version: " - 7.99.99"
+      reason: "implemented in 8.0.0"
+
+  - do:
+      indices.create:
+        index:  test
+        body:
+          mappings:
+            properties:
+              text:
+                type: text
+                analyzer: standard
+  - do:
+      bulk:
+        refresh: true
+        body:
+          - '{"index": {"_index": "test", "_id": "1"}}'
+          - '{"text" : "Some like it hot, some like it cold"}'
+          - '{"index": {"_index": "test", "_id": "2"}}'
+          - '{"text" : "Its cold outside, theres no kind of atmosphere"}'
+          - '{"index": {"_index": "test", "_id": "3"}}'
+          - '{"text" : "Baby its cold there outside"}'
+          - '{"index": {"_index": "test", "_id": "4"}}'
+          - '{"text" : "Outside it is cold and wet"}'
+
+---
+teardown:
+  - skip:
+      version: " - 7.99.99"
+      reason: "implemented in 8.0.0"
+
+  - do:
+      cluster.put_settings:
+        body:
+          transient:
+            search.disallow_slow_queries: null
+
+---
+"Test disallow slow queries":
+  - skip:
+      version: " - 7.99.99"
+      reason: "implemented in 8.0.0"
+
+  ### Check for initial setting = null -> false
+  - do:
+      cluster.get_settings:
+        flat_settings: true
+
+  - match: {search.disallow_slow_queries: null}
+
+  ### Prefix
+  - do:
+      search:
+        index: test
+        body:
+          query:
+            prefix:
+              text:
+                value: out
+
+  - match: { hits.total.value: 3 }
+
+  ### Fuzzy
+  - do:
+      search:
+        index: test
+        body:
+          query:
+            fuzzy:
+              text:
+                value: outwide
+
+  - match: { hits.total.value: 3 }
+
+
+  ### Regexp
+  - do:
+      search:
+        index: test
+        body:
+          query:
+            regexp:
+              text:
+                value: .*ou.*id.*
+
+  - match: { hits.total.value: 3 }
+
+  ### Wildcard
+  - do:
+      search:
+        index: test
+        body:
+          query:
+            wildcard:
+              text:
+                value: out?ide
+
+  - match: { hits.total.value: 3 }
+
+  ### Update setting to true
+  - do:
+      cluster.put_settings:
+        body:
+          transient:
+            search.disallow_slow_queries: "true"
+        flat_settings: true
+
+  - match: {transient: {search.disallow_slow_queries: "true"}}
+
+  ### Prefix
+  - do:
+      catch: /prefix queries cannot be executed when \'search.disallow_slow_queries\' is set to true/
+      search:
+        index: test
+        body:
+          query:
+            prefix:
+              text:
+                value: out
+
+  ### Fuzzy
+  - do:
+      catch: /fuzzy queries cannot be executed when \'search.disallow_slow_queries\' is set to true/
+      search:
+        index: test
+        body:
+          query:
+            fuzzy:
+              text:
+                value: outwide
+
+  ### Regexp
+  - do:
+      catch: /regexp queries cannot be executed when \'search.disallow_slow_queries\' is set to true/
+      search:
+        index: test
+        body:
+          query:
+            regexp:
+              text:
+                value: .*ou.*id.*
+
+  ### Wildcard
+  - do:
+      catch: /wildcard queries cannot be executed when \'search.disallow_slow_queries\' is set to true/
+      search:
+        index: test
+        body:
+          query:
+            wildcard:
+              text:
+                value: out?ide
+
+  ### Revert setting to false
+  - do:
+      cluster.put_settings:
+        body:
+          transient:
+            search.disallow_slow_queries: "false"
+        flat_settings: true
+
+  - match: {transient: {search.disallow_slow_queries: "false"}}
+
+  ### Prefix
+  - do:
+      search:
+        index: test
+        body:
+          query:
+            prefix:
+              text:
+                value: out
+
+  - match: { hits.total.value: 3 }
+
+  ### Fuzzy
+  - do:
+      search:
+        index: test
+        body:
+          query:
+            fuzzy:
+              text:
+                value: outwide
+
+  - match: { hits.total.value: 3 }
+
+  ### Regexp
+  - do:
+      search:
+        index: test
+        body:
+          query:
+            regexp:
+              text:
+                value: .*ou.*id.*
+
+  - match: { hits.total.value: 3 }
+
+  ### Wildcard
+  - do:
+      search:
+        index: test
+        body:
+          query:
+            wildcard:
+              text:
+                value: out?ide
+
+  - match: { hits.total.value: 3 }

server/src/main/java/org/elasticsearch/common/settings/ClusterSettings.java

@@ -388,6 +388,7 @@ public void apply(Settings value, Settings current, Settings previous) {
             SearchService.DEFAULT_KEEPALIVE_SETTING,
             SearchService.KEEPALIVE_INTERVAL_SETTING,
             SearchService.MAX_KEEPALIVE_SETTING,
+            SearchService.DISALLOW_SLOW_QUERIES,
             MultiBucketConsumerService.MAX_BUCKET_SETTING,
             SearchService.LOW_LEVEL_CANCELLATION_SETTING,
             SearchService.MAX_OPEN_SCROLL_CONTEXT,