adjust the FAQ doc of V1.2、latest and master version (#176)

apache · Feb 7, 2024 · b1f50d2 · b1f50d2
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diff --git a/src/UserGuide/Master/API/RestServiceV1.md b/src/UserGuide/Master/API/RestServiceV1.md
@@ -32,7 +32,7 @@ RESTful services are disabled by default.
 
 * User
 
-  Find the `conf/iotdb.rest.properties` file under the IoTDB installation directory and set `enable_rest_service` to `true` to enable the module.
+  Find the `conf/iotdb-datanode.properties` file under the IoTDB installation directory and set `enable_rest_service` to `true` to enable the module.
 
   ```properties
   enable_rest_service=true

diff --git a/src/UserGuide/Master/Deployment-and-Maintenance/Deployment-Guide_timecho.md b/src/UserGuide/Master/Deployment-and-Maintenance/Deployment-Guide_timecho.md
@@ -160,10 +160,10 @@ IOTDB_JMX_OPTS="$IOTDB_JMX_OPTS -XX:MaxGCPauseMillis=200"
 | parameter name              | parameter describe                                                                                                                                                                | required |
 |-----------------------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|----------|
 | name                        | Confignode name                                                                                                                                                                   | YES      |
-| deploy\_dir                 | IoTDB config node deployment directory                                                                                                                                                            | YES｜     |
+| deploy\_dir                 | IoTDB config node deployment directory                                                                                                                                                            | YES     |
 | iotdb-confignode.properties | Corresponding to `iotdb/config/iotdb-confignode.properties`, please refer to the `iotdb-confignode.properties` file description for more details.                                                                                             | NO       |
 | cn\_internal\_address       | Corresponds to iotdb/internal communication address, corresponding to `cn_internal_address` in `iotdb/config/iotdb-confignode.properties`                                                                                              | YES      |
-| cn_\internal\_address       | The cluster configuration address points to the surviving ConfigNode, and it points to confignode_x by default. When `global` and `confignode_servers` are configured at the same time, the value in `confignode_servers` is used first, corresponding to `cn_internal_address` in `iotdb/config/iotdb-confignode.properties` | YES      |
+| cn_internal_address       | The cluster configuration address points to the surviving ConfigNode, and it points to confignode_x by default. When `global` and `confignode_servers` are configured at the same time, the value in `confignode_servers` is used first, corresponding to `cn_internal_address` in `iotdb/config/iotdb-confignode.properties` | YES      |
 | cn\_internal\_port          | Internal communication port, corresponding to `cn_internal_port` in `iotdb/config/iotdb-confignode.properties`                                                                                                          | YES      |
 | cn\_consensus\_port         | Corresponds to `cn_consensus_port` in `iotdb/config/iotdb-confignode.properties`                                                                                                               | NO      |
 | cn\_data\_dir               | Corresponds to `cn_consensus_port` in `iotdb/config/iotdb-confignode.properties` Corresponds to `cn_data_dir` in `iotdb/config/iotdb-confignode.properties`                                                                                                                       | YES      |

diff --git a/src/UserGuide/Master/FAQ/Frequently-asked-questions.md b/src/UserGuide/Master/FAQ/Frequently-asked-questions.md
@@ -154,6 +154,25 @@ The default IoTDB's Cli time display format is readable (e.g. ```1970-01-01T08:0
 
 ### 9. How to handle error `IndexOutOfBoundsException` from `org.apache.ratis.grpc.server.GrpcLogAppender`?
 
+### 10. How to deal with estimated out of memory errors?
+
+Report an error message:
+```
+301: There is not enough memory to execute current fragment instance, current remaining free memory is 86762854, estimated memory usage for current fragment instance is 270139392
+```
+Error analysis:
+The datanode_memory_proportion parameter controls the memory divided to the query, and the chunk_timeseriesmeta_free_memory_proportion parameter controls the memory available for query execution.
+By default the memory allocated to the query is 30% of the heap memory and the memory available for query execution is 20% of the query memory.
+The error report shows that the current remaining memory available for query execution is 86762854B = 82.74MB, and the query is estimated to use 270139392B = 257.6MB of execution memory.
+
+Some possible improvement items:
+
+- Without changing the default parameters, crank up the heap memory of IoTDB greater than 4.2G (4.2G * 1024MB = 4300MB), 4300M * 30% * 20% = 258M > 257.6M, which can fulfill the requirement.
+- Change parameters such as datanode_memory_proportion so that the available memory for query execution is >257.6MB.
+- Reduce the number of exported time series.
+- Add slimit limit to the query statement, which is also an option to reduce the query time series.
+- Add align by device, which will export in device order, and the memory usage will be reduced to single-device level.
+
 It is an internal error introduced by Ratis 2.4.1 dependency, and we can safely ignore this exception as it will
 not affect normal operations. We will fix this message in the incoming releases.