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feat(stream)[TS-5469]: add event notification usage instructions 

Add usage syntax and detailed description of event notification fields
in the user man fields in the user manual.
This commit is contained in:
Jinqing Kuang 2025-02-16 23:22:42 +08:00
parent 8ad3a5802d
commit 77206771c8
2 changed files with 445 additions and 2 deletions
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224
docs/en/14-reference/03-taos-sql/14-stream.md
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@ -9,7 +9,7 @@ import imgStream from './assets/stream-processing-01.png';
## Creating Stream Computing
```sql
CREATE STREAM [IF NOT EXISTS] stream_name [stream_options] INTO stb_name[(field1_name, field2_name [PRIMARY KEY], ...)] [TAGS (create_definition [, create_definition] ...)] SUBTABLE(expression) AS subquery
CREATE STREAM [IF NOT EXISTS] stream_name [stream_options] INTO stb_name[(field1_name, field2_name [PRIMARY KEY], ...)] [TAGS (create_definition [, create_definition] ...)] SUBTABLE(expression) AS subquery [notification_definition]
stream_options: {
TRIGGER [AT_ONCE | WINDOW_CLOSE | MAX_DELAY time | FORCE_WINDOW_CLOSE]
WATERMARK time
@ -85,6 +85,8 @@ CREATE STREAM streams1 IGNORE EXPIRED 1 WATERMARK 100s INTO streamt1 AS
SELECT _wstart, count(*), avg(voltage) from meters PARTITION BY tbname COUNT_WINDOW(10);
```
notification_definition clause specifies the addresses to which notifications should be sent when designated events occur during window computations, such as window opening or closing. For more details, see [Stream Computing Event Notifications](#stream-computing-event-notifications).
## Stream Computation Partitioning
You can use `PARTITION BY TBNAME`, tags, regular columns, or expressions to partition a stream for multi-partition computation. Each partition's timeline and window are independent, aggregating separately, and writing into different subtables of the target table.
@ -305,3 +307,223 @@ CREATE SNODE ON DNODE [id]
The id is the serial number of the dnode in the cluster. Please be mindful of the selected dnode, as the intermediate state of stream computing will automatically be backed up on it.
Starting from version 3.3.4.0, in a multi-replica environment, creating a stream will perform an **existence check** of snode, requiring the snode to be created first. If the snode does not exist, the stream cannot be created.
## Stream Computing Event Notifications
### User Guide
Stream computing supports sending event notifications to external systems when windows open or close. Users can specify the events to be notified and the target addresses for receiving notification messages using the notification_definition clause.
```sql
notification_definition:
NOTIFY (url [, url] ...) ON (event_type [, event_type] ...) [notification_options]
event_type:
'WINDOW_OPEN'
| 'WINDOW_CLOSE'
notification_options: {
NOTIFY_HISTORY [0|1]
ON_FAILURE [DROP|PAUSE]
}
```
The rules for the syntax above are as follows:
1. `url`: Specifies the target address for the notification. It must include the protocol, IP or domain name, port, and may include a path and parameters. Currently, only the websocket protocol is supported. For example: 'ws://localhost:8080', 'ws://localhost:8080/notify', 'wss://localhost:8080/notify?key=foo'.
2. `event_type`: Defines the events that trigger notifications. Supported event types include:
1. 'WINDOW_OPEN': Window open event; triggered when any type of window opens.
2. 'WINDOW_CLOSE': Window close event; triggered when any type of window closes.
3. `NOTIFY_HISTORY`: Controls whether to trigger notifications during the computation of historical data. The default value is 0, which means no notifications are sent.
4. `ON_FAILURE`: Determines whether to allow dropping some events if sending notifications fails (e.g., in poor network conditions). The default value is `PAUSE`:
1. PAUSE means that the stream computing task is paused if sending a notification fails. taosd will retry until the notification is successfully delivered and the task resumes.
2. DROP means that if sending a notification fails, the event information is discarded, and the stream computing task continues running unaffected.
For example, the following creates a stream that computes the per-minute average current from electric meters and sends notifications to two target addresses when the window opens and closes. It does not send notifications for historical data and does not allow dropping notifications on failure:
```sql
CREATE STREAM avg_current_stream FILL_HISTORY 1
AS SELECT _wstart, _wend, AVG(current) FROM meters
INTERVAL (1m)
NOTIFY ('ws://localhost:8080/notify', 'wss://192.168.1.1:8080/notify?key=foo')
ON ('WINDOW_OPEN', 'WINDOW_CLOSE');
NOTIFY_HISTORY 0
ON_FAILURE PAUSE;
```
When the specified events are triggered, taosd will send a POST request to the given URL(s) with a JSON message body. A single request may contain events from several streams, and the event types may differ.
The details of the event information depend on the type of window:
1. Time Window: At the opening, the start time is sent; at the closing, the start time, end time, and computation result are sent.
2. State Window: At the opening, the start time, previous window's state, and current window's state are sent; at closing, the start time, end time, computation result, current window state, and next window state are sent.
3. Session Window: At the opening, the start time is sent; at the closing, the start time, end time, and computation result are sent.
4. Event Window: At the opening, the start time along with the data values and corresponding condition index that triggered the window opening are sent; at the closing, the start time, end time, computation result, and the triggering data value and condition index for window closure are sent.
5. Count Window: At the opening, the start time is sent; at the closing, the start time, end time, and computation result are sent.
An example structure for the notification message is shown below:
```json
{
"messageId": "unique-message-id-12345",
"timestamp": 1733284887203,
"streams": [
{
"streamName": "avg_current_stream",
"events": [
{
"tableName": "t_a667a16127d3b5a18988e32f3e76cd30",
"eventType": "WINDOW_OPEN",
"eventTime": 1733284887097,
"windowId": "window-id-67890",
"windowType": "Time",
"windowStart": 1733284800000
},
{
"tableName": "t_a667a16127d3b5a18988e32f3e76cd30",
"eventType": "WINDOW_CLOSE",
"eventTime": 1733284887197,
"windowId": "window-id-67890",
"windowType": "Time",
"windowStart": 1733284800000,
"windowEnd": 1733284860000,
"result": {
"_wstart": 1733284800000,
"avg(current)": 1.3
}
}
]
},
{
"streamName": "max_voltage_stream",
"events": [
{
"tableName": "t_96f62b752f36e9b16dc969fe45363748",
"eventType": "WINDOW_OPEN",
"eventTime": 1733284887231,
"windowId": "window-id-13579",
"windowType": "Event",
"windowStart": 1733284800000,
"triggerCondition": {
"conditionIndex": 0,
"fieldValue": {
"c1": 10,
"c2": 15
}
},
},
{
"tableName": "t_96f62b752f36e9b16dc969fe45363748",
"eventType": "WINDOW_CLOSE",
"eventTime": 1733284887231,
"windowId": "window-id-13579",
"windowType": "Event",
"windowStart": 1733284800000,
"windowEnd": 1733284810000,
"triggerCondition": {
"conditionIndex": 1,
"fieldValue": {
"c1": 20
"c2": 3
}
},
"result": {
"_wstart": 1733284800000,
"max(voltage)": 220
}
}
]
}
]
}
```
The following sections explain the fields in the notification message.
### Root-Level Field Descriptions
1. "messageId": A string that uniquely identifies the notification message. It ensures that the entire message can be tracked and de-duplicated.
2. "timestamp": A long integer timestamp representing the time when the notification message was generated, accurate to the millisecond (i.e., the number of milliseconds since '00:00, Jan 1 1970 UTC').
3. "streams": An array containing the event information for multiple stream tasks. (See the following sections for details.)
### "stream" Object Field Descriptions
1. "streamName": A string representing the name of the stream task, used to identify which stream the events belong to.
2. "events": An array containing the list of event objects for the stream task. Each event object includes detailed information. (See the next sections for details.)
### "event" Object Field Descriptions
#### Common Fields
These fields are common to all event objects.
1. "tableName": A string indicating the name of the target subtable.
2. "eventType": A string representing the event type ("WINDOW_OPEN", "WINDOW_CLOSE", or "WINDOW_INVALIDATION").
3. "eventTime": A long integer timestamp that indicates when the event was generated, accurate to the millisecond (i.e., the number of milliseconds since '00:00, Jan 1 1970 UTC').
4. "windowId": A string representing the unique identifier for the window. This ID ensures that the open and close events for the same window can be correlated. In the case that taosd restarts due to a fault, some events may be sent repeatedly, but the windowId remains constant for the same window.
5. "windowType": A string that indicates the window type ("Time", "State", "Session", "Event", or "Count").
#### Fields for Time Windows
These fields are present only when "windowType" is "Time".
1. When "eventType" is "WINDOW_OPEN", the following field is included:
1. "windowStart": A long integer timestamp representing the start time of the window, matching the time precision of the result table.
2. When "eventType" is "WINDOW_CLOSE", the following fields are included:
1. "windowStart": A long integer timestamp representing the start time of the window.
1. "windowEnd": A long integer timestamp representing the end time of the window.
1. "result": An object containing key-value pairs of the computed result columns and their corresponding values.
#### Fields for State Windows
These fields are present only when "windowType" is "State".
1. When "eventType" is "WINDOW_OPEN", the following fields are included:
1. "windowStart": A long integer timestamp representing the start time of the window.
1. "prevState": A value of the same type as the state column, representing the state of the previous window. If there is no previous window (i.e., this is the first window), it will be NULL.
1. "curState": A value of the same type as the state column, representing the current window's state.
2. When "eventType" is "WINDOW_CLOSE", the following fields are included:
1. "windowStart": A long integer timestamp representing the start time of the window.
1. "windowEnd": A long integer timestamp representing the end time of the window.
1. "curState": The current window's state.
1. "nextState": The state for the next window.
1. "result": An object containing key-value pairs of the computed result columns and their corresponding values.
#### Fields for Session Windows
These fields are present only when "windowType" is "Session".
1. When "eventType" is "WINDOW_OPEN", the following field is included:
1. "windowStart": A long integer timestamp representing the start time of the window.
2. When "eventType" is "WINDOW_CLOSE", the following fields are included:
1. "windowStart": A long integer timestamp representing the start time of the window.
1. "windowEnd": A long integer timestamp representing the end time of the window.
1. "result": An object containing key-value pairs of the computed result columns and their corresponding values.
#### Fields for Event Windows
These fields are present only when "windowType" is "Event".
1. When "eventType" is "WINDOW_OPEN", the following fields are included:
1. "windowStart": A long integer timestamp representing the start time of the window.
1. "triggerCondition": An object that provides information about the condition that triggered the window to open. It includes:
1. "conditionIndex": An integer representing the index of the condition that triggered the window, starting from 0.
1. "fieldValue": An object containing key-value pairs of the column names related to the condition and their respective values.
2. When "eventType" is "WINDOW_CLOSE", the following fields are included:
1. "windowStart": A long integer timestamp representing the start time of the window.
1. "windowEnd": A long integer timestamp representing the end time of the window.
1. "triggerCondition": An object that provides information about the condition that triggered the window to close. It includes:
1. "conditionIndex": An integer representing the index of the condition that triggered the closure, starting from 0.
1. "fieldValue": An object containing key-value pairs of the related column names and their respective values.
1. "result": An object containing key-value pairs of the computed result columns and their corresponding values.
#### Fields for Count Windows
These fields are present only when "windowType" is "Count".
1. When "eventType" is "WINDOW_OPEN", the following field is included:
1. "windowStart": A long integer timestamp representing the start time of the window.
2. When "eventType" is "WINDOW_CLOSE", the following fields are included:
1. "windowStart": A long integer timestamp representing the start time of the window.
1. "windowEnd": A long integer timestamp representing the end time of the window.
1. "result": An object containing key-value pairs of the computed result columns and their corresponding values.
#### Fields for Window Invalidation
Due to scenarios such as data disorder, updates, or deletions during stream computing, windows that have already been generated might be removed or their results need to be recalculated. In such cases, a notification with the eventType "WINDOW_INVALIDATION" is sent to inform which windows have been invalidated.
For events with "eventType" as "WINDOW_INVALIDATION", the following fields are included:
1. "windowStart": A long integer timestamp representing the start time of the window.
1. "windowEnd": A long integer timestamp representing the end time of the window.

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@ -8,7 +8,7 @@ description: 流式计算的相关 SQL 的详细语法
## 创建流式计算
```sql
CREATE STREAM [IF NOT EXISTS] stream_name [stream_options] INTO stb_name[(field1_name, field2_name [PRIMARY KEY], ...)] [TAGS (create_definition [, create_definition] ...)] SUBTABLE(expression) AS subquery
CREATE STREAM [IF NOT EXISTS] stream_name [stream_options] INTO stb_name[(field1_name, field2_name [PRIMARY KEY], ...)] [TAGS (create_definition [, create_definition] ...)] SUBTABLE(expression) AS subquery [notification_definition]
stream_options: {
TRIGGER [AT_ONCE | WINDOW_CLOSE | MAX_DELAY time | FORCE_WINDOW_CLOSE]
WATERMARK time
@ -83,6 +83,8 @@ CREATE STREAM streams1 IGNORE EXPIRED 1 WATERMARK 100s INTO streamt1 AS
SELECT _wstart, count(*), avg(voltage) from meters PARTITION BY tbname COUNT_WINDOW(10);
```
notification_definition 子句定义了窗口计算过程中，在窗口打开/关闭等指定事件发生时，需要向哪些地址发送通知。详见 [流式计算的事件通知](#流失计算的事件通知)
## 流式计算的 partition
可以使用 PARTITION BY TBNAME，tag，普通列或者表达式，对一个流进行多分区的计算，每个分区的时间线与时间窗口是独立的，会各自聚合，并写入到目的表中的不同子表。
@ -297,3 +299,222 @@ CREATE SNODE ON DNODE [id]
```
其中的 id 是集群中的 dnode 的序号。请注意选择的dnode，流计算的中间状态将自动在其上进行备份。
从 3.3.4.0 版本开始，在多副本环境中创建流会进行 snode 的**存在性检查**，要求首先创建 snode。如果 snode 不存在，无法创建流。
## 流式计算的事件通知
### 使用说明
流式计算支持在窗口打开/关闭时，向外部系统发送相关的事件通知。用户通过 notification_definition 来指定需要通知的事件，以及用于接收通知消息的目标地址。
```sql
notification_definition:
NOTIFY (url [, url] ...) ON (event_type [, event_type] ...) [notification_options]
event_type:
'WINDOW_OPEN'
| 'WINDOW_CLOSE'
notification_options: {
NOTIFY_HISTORY [0|1]
ON_FAILURE [DROP|PAUSE]
}
```
上述语法中的相关规则含义如下：
1. `url`: 指定通知的目标地址，必须包括协议、IP 或域名、端口号，并允许包含路径、参数。目前仅支持 websocket 协议。例如：'ws://localhost:8080'，'ws://localhost:8080/notify'，'wss://localhost:8080/notify?key=foo'。
1. `event_type`: 定义需要通知的事件，支持的事件类型有:
1. 'WINDOW_OPEN'：窗口打开事件，所有类型的窗口打开时都会触发
1. 'WINDOW_CLOSE'：窗口关闭事件，所有类型的窗口关闭时都会触发
1. `NOTIFY_HISTORY`: 控制是否在计算历史数据时触发通知，默认值为0，即不触发
1. `ON_FAILURE`: 向通知地址发送通知失败时(比如网络不佳场景)是否允许丢弃部分事件，默认值为 `PAUSE`
1. PAUSE 表示发送通知失败时暂停流计算任务。taosd 会重试发送通知，直到发送成功后，任务自动恢复运行。
1. DROP 表示发送通知失败时直接丢弃事件信息，流计算任务继续运行，不受影响
比如，以下示例创建一个流，计算电表电流的每分钟平均值，并在窗口打开、关闭时向两个通知地址发送通知，计算历史数据时不发送通知，不允许在通知发送失败时丢弃通知：
```sql
CREATE STREAM avg_current_stream FILL_HISTORY 1
AS SELECT _wstart, _wend, AVG(current) FROM meters
INTERVAL (1m)
NOTIFY ('ws://localhost:8080/notify', 'wss://192.168.1.1:8080/notify?key=foo')
ON ('WINDOW_OPEN', 'WINDOW_CLOSE');
NOTIFY_HISTORY 0
ON_FAILURE PAUSE;
```
当触发指定的事件时，taosd 会向指定的 URL 发送 POST 请求，消息体为 JSON 格式。一个请求可能包含若干个流的若干个事件，且事件类型不一定相同。
事件信息视窗口类型而定：
1. 时间窗口：开始时发送起始时间；结束时发送起始时间、结束时间、计算结果。
1. 状态窗口：开始时发送起始时间、前一个窗口的状态值、当前窗口的状态值；结束时发送起始时间、结束时间、计算结果、当前窗口的状态值、下一个窗口的状态值。
1. 会话窗口：开始时发送起始时间；结束时发送起始时间、结束时间、计算结果。
1. 事件窗口：开始时发送起始时间，触发窗口打开的数据值和对应条件编号；结束时发送起始时间、结束时间、计算结果、触发窗口关闭的数据值和对应条件编号。
1. 计数窗口：开始时发送起始时间；结束时发送起始时间、结束时间、计算结果。
通知消息的结构示例如下：
```json
{
"messageId": "unique-message-id-12345",
"timestamp": 1733284887203,
"streams": [
{
"streamName": "avg_current_stream",
"events": [
{
"tableName": "t_a667a16127d3b5a18988e32f3e76cd30",
"eventType": "WINDOW_OPEN",
"eventTime": 1733284887097,
"windowId": "window-id-67890",
"windowType": "Time",
"windowStart": 1733284800000
},
{
"tableName": "t_a667a16127d3b5a18988e32f3e76cd30",
"eventType": "WINDOW_CLOSE",
"eventTime": 1733284887197,
"windowId": "window-id-67890",
"windowType": "Time",
"windowStart": 1733284800000,
"windowEnd": 1733284860000,
"result": {
"_wstart": 1733284800000,
"avg(current)": 1.3
}
}
]
},
{
"streamName": "max_voltage_stream",
"events": [
{
"tableName": "t_96f62b752f36e9b16dc969fe45363748",
"eventType": "WINDOW_OPEN",
"eventTime": 1733284887231,
"windowId": "window-id-13579",
"windowType": "Event",
"windowStart": 1733284800000,
"triggerCondition": {
"conditionIndex": 0,
"fieldValue": {
"c1": 10,
"c2": 15
}
},
},
{
"tableName": "t_96f62b752f36e9b16dc969fe45363748",
"eventType": "WINDOW_CLOSE",
"eventTime": 1733284887231,
"windowId": "window-id-13579",
"windowType": "Event",
"windowStart": 1733284800000,
"windowEnd": 1733284810000,
"triggerCondition": {
"conditionIndex": 1,
"fieldValue": {
"c1": 20
"c2": 3
}
},
"result": {
"_wstart": 1733284800000,
"max(voltage)": 220
}
}
]
}
]
}
```
后续小节是通知消息中各个字段的说明。
### 根级字段说明
1. "messageId": 字符串类型，是通知消息的唯一标识符，确保整条消息可以被追踪和去重。
1. "timestamp": 长整型时间戳，表示通知消息生成的时间，精确到毫秒，即: '00:00, Jan 1 1970 UTC' 以来的毫秒数。
1. "streams": 对象数组，包含多个流任务的事件信息。(详细信息见下节)
### stream 对象的字段说明
1. "streamName": 字符串类型，流任务的名称，用于标识事件所属的流。
1. "events": 对象数组，该流任务下的事件列表，包含一个或多个事件对象。(详细信息见下节)
### event 对象的字段说明
#### 通用字段
这部分是所有 event 对象所共有的字段。
1. "tableName": 字符串类型，是对应目标子表的表名。
1. "eventType": 字符串类型，表示事件类型 ("WINDOW_OPEN", "WINDOW_CLOSE" 或 "WINDOW_INVALIDATION")。
1. "eventTime": 长整型时间戳，表示事件生成时间，精确到毫秒，即: '00:00, Jan 1 1970 UTC' 以来的毫秒数。
1. "windowId": 字符串类型，窗口的唯一标识符，确保打开和关闭事件的 ID 一致，便于外部系统将两者关联。如果 taosd 发生故障重启，部分事件可能会重复发送，会保证同一窗口的 windowId 保持不变。
1. "windowType": 字符串类型，表示窗口类型 ("Time", "State", "Session", "Event", "Count")。
#### 时间窗口相关字段
这部分是 "windowType" 为"Time" 时 event 对象才有的字段。
1. 如果 "eventType" 为 "WINDOW_OPEN"，则包含如下字段：
1. "windowStart": 长整型时间戳，表示窗口的开始时间，精度与结果表的时间精度一致。
1. 如果 "eventType" 为 "WINDOW_CLOSE"，则包含如下字段：
1. "windowStart": 长整型时间戳，表示窗口的开始时间，精度与结果表的时间精度一致。
1. "windowEnd": 长整型时间戳，表示窗口的结束时间，精度与结果表的时间精度一致。
1. "result": 计算结果，为键值对形式，包含窗口计算的结果列列名及其对应的值。
#### 状态窗口相关字段
这部分是 "windowType" 为"State" 时 event 对象才有的字段。
1. 如果 "eventType" 为 "WINDOW_OPEN"，则包含如下字段：
1. "windowStart": 长整型时间戳，表示窗口的开始时间，精度与结果表的时间精度一致。
1. "prevState": 与状态列的类型相同，表示上一个窗口的状态值。如果没有上一个窗口(即: 现在是第一个窗口)，则为 NULL。
1. "curState": 与状态列的类型相同，表示当前窗口的状态值。
1. 如果 "eventType" 为 "WINDOW_CLOSE"，则包含如下字段：
1. "windowStart": 长整型时间戳，表示窗口的开始时间，精度与结果表的时间精度一致。
1. "windowEnd": 长整型时间戳，表示窗口的结束时间，精度与结果表的时间精度一致。
1. "curState": 与状态列的类型相同，表示当前窗口的状态值。
1. "nextState": 与状态列的类型相同，表示下一个窗口的状态值。
1. "result": 计算结果，为键值对形式，包含窗口计算的结果列列名及其对应的值。
#### 会话窗口相关字段
这部分是 "windowType" 为"Session" 时 event 对象才有的字段。
1. 如果 "eventType" 为 "WINDOW_OPEN"，则包含如下字段：
1. "windowStart": 长整型时间戳，表示窗口的开始时间，精度与结果表的时间精度一致。
1. 如果 "eventType" 为 "WINDOW_CLOSE"，则包含如下字段：
1. "windowStart": 长整型时间戳，表示窗口的开始时间，精度与结果表的时间精度一致。
1. "windowEnd": 长整型时间戳，表示窗口的结束时间，精度与结果表的时间精度一致。
1. "result": 计算结果，为键值对形式，包含窗口计算的结果列列名及其对应的值。
#### 事件窗口相关字段
这部分是 "windowType" 为"Event" 时 event 对象才有的字段。
1. 如果 "eventType" 为 "WINDOW_OPEN"，则包含如下字段：
1. "windowStart": 长整型时间戳，表示窗口的开始时间，精度与结果表的时间精度一致。
1. "triggerCondition": 触发窗口开始的条件信息，包括以下字段：
1. "conditionIndex": 整型，表示满足的触发窗口开始的条件的索引，从0开始编号。
1. "fieldValue": 键值对形式，包含条件列列名及其对应的值。
1. 如果 "eventType" 为 "WINDOW_CLOSE"，则包含如下字段：
1. "windowStart": 长整型时间戳，表示窗口的开始时间，精度与结果表的时间精度一致。
1. "windowEnd": 长整型时间戳，表示窗口的结束时间，精度与结果表的时间精度一致。
1. "triggerCondition": 触发窗口关闭的条件信息，包括以下字段：
1. "conditionIndex": 整型，表示满足的触发窗口关闭的条件的索引，从0开始编号。
1. "fieldValue": 键值对形式，包含条件列列名及其对应的值。
1. "result": 计算结果，为键值对形式，包含窗口计算的结果列列名及其对应的值。
#### 计数窗口相关字段
这部分是 "windowType" 为"Count" 时 event 对象才有的字段。
1. 如果 "eventType" 为 "WINDOW_OPEN"，则包含如下字段：
1. "windowStart": 长整型时间戳，表示窗口的开始时间，精度与结果表的时间精度一致。
1. 如果 "eventType" 为 "WINDOW_CLOSE"，则包含如下字段：
1. "windowStart": 长整型时间戳，表示窗口的开始时间，精度与结果表的时间精度一致。
1. "windowEnd": 长整型时间戳，表示窗口的结束时间，精度与结果表的时间精度一致。
1. "result": 计算结果，为键值对形式，包含窗口计算的结果列列名及其对应的值。
#### 窗口失效相关字段
因为流计算过程中会遇到数据乱序、更新、删除等情况，可能造成已生成的窗口被删除，或者结果需要重新计算。此时会向通知地址发送一条 "WINDOW_INVALIDATION" 的通知，说明哪些窗口已经被删除。
这部分是 "eventType" 为 "WINDOW_INVALIDATION" 时，event 对象才有的字段。
1. "windowStart": 长整型时间戳，表示窗口的开始时间，精度与结果表的时间精度一致。
1. "windowEnd": 长整型时间戳，表示窗口的结束时间，精度与结果表的时间精度一致。