[FLINK-26159][doc] add description for MAX_FETCH_RECORD related question
Update docs/content/docs/connectors/datastream/pulsar.md
Co-authored-by: MartijnVisser <martijn@2symbols.com>
Update docs/content/docs/connectors/datastream/pulsar.md
Co-authored-by: MartijnVisser <martijn@2symbols.com>
add Chinese documentation
diff --git a/docs/content.zh/docs/connectors/datastream/pubsub.md b/docs/content.zh/docs/connectors/datastream/pubsub.md
index f766374..837b892 100644
--- a/docs/content.zh/docs/connectors/datastream/pubsub.md
+++ b/docs/content.zh/docs/connectors/datastream/pubsub.md
@@ -150,4 +150,21 @@
Sink function 会把准备发到 PubSub 的信息短暂地缓存以提高性能。每次 checkpoint 前，它会刷新缓冲区，并且只有当所有信息成功发送到 PubSub 之后，checkpoint 才会成功完成。
+## 常见问题
+
+由于Pulsar Connector大量依赖
+[PulsarClient](https://pulsar.apache.org/docs/en/client-libraries-java/) 和
+[PulsarAdmin](https://pulsar.apache.org/docs/en/admin-api-overview/) 来实现相关功能，有时Flink Job出现
+可能是由于Pulsar broker版本过低或者配置不合适导致的。调试配置或升级pulsar可能会解决部分问题。
+
+
+### 当数据量很小时，source读数据出现大约10s延迟
+
+当Pulsar Source从一个数据量很小的topic读取数据时，用户可能会观测到消息间出现10秒钟的间隔。这是由于Pulsar Source
+会将从broker读到的消息暂存至等待队列中，只有当队列中消息数量达到了 `PulsarSourceOptions.PULSAR_MAX_FETCH_RECORDS`
+才会向下游算子发送数据。如果数据量一直很小，那么就会在等待直到等待时长超过`PULSAR_MAX_FETCH_TIME`规定的值 (默认10秒钟)时
+也向下游算子发送数据。
+
+为了避免这种情况，用户需要改变两个配置项的值。
+
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diff --git a/docs/content/docs/connectors/datastream/pulsar.md b/docs/content/docs/connectors/datastream/pulsar.md
index 680fb1a..6e89174 100644
--- a/docs/content/docs/connectors/datastream/pulsar.md
+++ b/docs/content/docs/connectors/datastream/pulsar.md
@@ -417,4 +417,13 @@
and your problem might be independent of Flink and sometimes can be solved by upgrading Pulsar brokers,
reconfiguring Pulsar brokers or reconfiguring Pulsar connector in Flink.
+### Messages can be delayed on low volume topics
+
+When the Pulsar source connector reads from a low volume topic, users might observe a 10 seconds delay between messages. Pulsar buffers messages from topics by default. Before emitting to downstream
+operators, the number of buffered records must be equal or larger than `PulsarSourceOptions.PULSAR_MAX_FETCH_RECORDS`. If the data volume is low, it could be that filling up the number of buffered records takes longer than `PULSAR_MAX_FETCH_TIME` (default to 10 seconds). If that's the case, it means that only after this time has passed the messages will be emitted.
+
+To avoid this behaviour, you need to change either the buffered records or the waiting time.
+
+
+
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