Reword exception message (#110481)

Rewords the exception message to make it clear the documents limit is per shard, not per index.

server/src/internalClusterTest/java/org/elasticsearch/index/engine/MaxDocsLimitIT.java

@@ -102,7 +102,7 @@ public class MaxDocsLimitIT extends ESIntegTestCase {
         assertThat(indexingResult.numFailures, equalTo(rejectedRequests));
         assertThat(indexingResult.numSuccess, equalTo(0));
         final IllegalArgumentException deleteError = expectThrows(IllegalArgumentException.class, client().prepareDelete("test", "any-id"));
-        assertThat(deleteError.getMessage(), containsString("Number of documents in the index can't exceed [" + maxDocs.get() + "]"));
+        assertThat(deleteError.getMessage(), containsString("Number of documents in the shard cannot exceed [" + maxDocs.get() + "]"));
         indicesAdmin().prepareRefresh("test").get();
         assertNoFailuresAndResponse(
             prepareSearch("test").setQuery(new MatchAllQueryBuilder()).setTrackTotalHitsUpTo(Integer.MAX_VALUE).setSize(0),
@@ -162,7 +162,7 @@ public class MaxDocsLimitIT extends ESIntegTestCase {
                     assertThat(resp.status(), equalTo(RestStatus.CREATED));
                 } catch (IllegalArgumentException e) {
                     numFailure.incrementAndGet();
-                    assertThat(e.getMessage(), containsString("Number of documents in the index can't exceed [" + maxDocs.get() + "]"));
+                    assertThat(e.getMessage(), containsString("Number of documents in the shard cannot exceed [" + maxDocs.get() + "]"));
                 }
             }
         });

server/src/main/java/org/elasticsearch/index/engine/InternalEngine.java

@@ -1688,7 +1688,7 @@ public class InternalEngine extends Engine {
         final long totalDocs = indexWriter.getPendingNumDocs() + inFlightDocCount.addAndGet(addingDocs);
         if (totalDocs > maxDocs) {
             releaseInFlightDocs(addingDocs);
-            return new IllegalArgumentException("Number of documents in the index can't exceed [" + maxDocs + "]");
+            return new IllegalArgumentException("Number of documents in the shard cannot exceed [" + maxDocs + "]");
         } else {
             return null;
         }

server/src/test/java/org/elasticsearch/index/engine/InternalEngineTests.java

@@ -7417,7 +7417,7 @@ public class InternalEngineTests extends EngineTestCase {
                     assertNotNull(result.getFailure());
                     assertThat(
                         result.getFailure().getMessage(),
-                        containsString("Number of documents in the index can't exceed [" + maxDocs + "]")
+                        containsString("Number of documents in the shard cannot exceed [" + maxDocs + "]")
                     );
                     assertThat(result.getSeqNo(), equalTo(UNASSIGNED_SEQ_NO));
                     assertThat(engine.getLocalCheckpointTracker().getMaxSeqNo(), equalTo(maxSeqNo));