GEODE-10052: Fix flakiness in OutOfMemoryDUnitTest (apache#7369)

- Add larger values to get over critical memory threshold faster and
 make it more likely to stay there
 - Force GC before each attempt to add a large value to make it less
 likely that we'll drop back below critical threshold due to small
 objects being GCd while over critical threshold

geode-for-redis/src/distributedTest/java/org/apache/geode/redis/OutOfMemoryDUnitTest.java

@@ -76,7 +76,8 @@ public class OutOfMemoryDUnitTest {
 
   private static final long KEY_TTL_SECONDS = 10;
   private static final int MAX_ITERATION_COUNT = 4000;
-  private static final int LARGE_VALUE_SIZE = 128 * 1024;
+  private static final int LARGE_VALUE_SIZE = 1024 * 1024;
+  private static final String LARGE_VALUE = StringUtils.leftPad("a", LARGE_VALUE_SIZE);
   private static final String KEY = "key";
 
   private static String locatorPort;
@@ -265,11 +266,10 @@ public void shouldAllowWriteOperations_afterDroppingBelowCriticalThreshold() {
 
     memoryPressure.cancel(true);
 
-    String value = StringUtils.leftPad("a", LARGE_VALUE_SIZE);
     await().untilAsserted(() -> assertThatNoException().isThrownBy(
         () -> {
           removeAllKeysAndForceGC();
-          jedis.set(server1Tag + "newKey", value);
+          jedis.set(server1Tag + "newKey", LARGE_VALUE);
         }));
   }
 
@@ -285,11 +285,10 @@ public void shouldAllowWriteOperations_onOtherServer_afterDroppingBelowCriticalT
 
     memoryPressure.cancel(true);
 
-    String value = StringUtils.leftPad("a", LARGE_VALUE_SIZE);
     await().untilAsserted(() -> assertThatNoException().isThrownBy(
         () -> {
           removeAllKeysAndForceGC();
-          jedis.set(server2Tag + "newKey", value);
+          jedis.set(server2Tag + "newKey", LARGE_VALUE);
         }));
   }
 
@@ -338,34 +337,26 @@ public void shouldAllowPublish_afterDroppingBelowCriticalThreshold() {
   }
 
   private void fillServer1Memory(JedisCluster jedis, boolean withExpiration) {
-    String valueString = StringUtils.leftPad("a", LARGE_VALUE_SIZE);
-
-    while (valueString.length() > 1) {
-      addMultipleKeysToServer1UntilOOMExceptionIsThrown(jedis, valueString, withExpiration);
-      valueString = valueString.substring(valueString.length() / 2);
-    }
-  }
-
-  private void maintainMemoryPressure(JedisCluster jedis, boolean withExpiration) {
-    while (!Thread.interrupted()) {
-      fillServer1Memory(jedis, withExpiration);
-    }
-  }
-
-  private void addMultipleKeysToServer1UntilOOMExceptionIsThrown(JedisCluster jedis,
-      String valueString, boolean withExpiration) {
     assertThatThrownBy(() -> {
+      // First force GC to reduce the chances of dropping back below critical accidentally
+      gfsh.execute("gc");
       for (int count = 0; count < MAX_ITERATION_COUNT; ++count) {
         if (withExpiration) {
-          jedis.setex(server1Tag + KEY + numberOfKeys.get(), KEY_TTL_SECONDS, valueString);
+          jedis.setex(server1Tag + KEY + numberOfKeys.get(), KEY_TTL_SECONDS, LARGE_VALUE);
         } else {
-          jedis.set(server1Tag + KEY + numberOfKeys.get(), valueString);
+          jedis.set(server1Tag + KEY + numberOfKeys.get(), LARGE_VALUE);
         }
         numberOfKeys.incrementAndGet();
       }
     }).hasMessageContaining("OOM command not allowed");
   }
 
+  private void maintainMemoryPressure(JedisCluster jedis, boolean withExpiration) {
+    while (!Thread.interrupted()) {
+      fillServer1Memory(jedis, withExpiration);
+    }
+  }
+
   void removeAllKeysAndForceGC() throws Exception {
     // Remove all the keys to allow memory to drop below critical
     Set<String> keys = jedis.keys(server1Tag + "*");