Update documentation of transactions page.

Closes #2865
Original pull request: #2870

Author: egor-ponomarev

src/main/antora/modules/ROOT/pages/redis/transactions.adoc

@@ -25,6 +25,31 @@ System.out.println("Number of items added to set: " + txResults.get(0));
 `RedisTemplate` uses its value, hash key, and hash value serializers to deserialize all results of `exec` before returning.
 There is an additional `exec` method that lets you pass a custom serializer for transaction results.
 
+It is worth mentioning that if between the commands multi() and exec() a query timeout exception happens (e.g. in case
+Redis is not available to respond fast) then the connection may get stuck in a transactional state. To prevent
+such situation you have to control the transaction state:
+
+[source,java]
+----
+List<Object> txResults = redisOperations.execute(new SessionCallback<List<Object>>() {
+  public List<Object> execute(RedisOperations operations) throws DataAccessException {
+    boolean transactionStateIsActive = true;
+	try {
+      operations.multi();
+      operations.opsForSet().add("key", "value1");
+
+      // This will contain the results of all operations in the transaction
+      return operations.exec();
+    } finally{
+      if (transactionStateIsActive) {
+        LOG.error("Transaction state is active");
+	    operations.discard();
+      }
+    }
+  }
+});
+----
+
 [[tx.spring]]
 == `@Transactional` Support