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Posted to commits@flink.apache.org by fh...@apache.org on 2017/06/15 09:44:06 UTC
[05/10] flink git commit: [FLINK-6747] [table] [docs] Time attributes
section added
[FLINK-6747] [table] [docs] Time attributes section added
This closes #4020.
Project: http://git-wip-us.apache.org/repos/asf/flink/repo
Commit: http://git-wip-us.apache.org/repos/asf/flink/commit/a29a9adb
Tree: http://git-wip-us.apache.org/repos/asf/flink/tree/a29a9adb
Diff: http://git-wip-us.apache.org/repos/asf/flink/diff/a29a9adb
Branch: refs/heads/master
Commit: a29a9adb8958cbb283a7cdfa24829cc66699e7e4
Parents: a5d93a5
Author: twalthr <tw...@apache.org>
Authored: Tue May 30 17:26:07 2017 +0200
Committer: Fabian Hueske <fh...@apache.org>
Committed: Thu Jun 15 11:42:18 2017 +0200
----------------------------------------------------------------------
docs/dev/table/streaming.md | 309 ++++++++++++++++++++++++++++++++++++++-
1 file changed, 302 insertions(+), 7 deletions(-)
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http://git-wip-us.apache.org/repos/asf/flink/blob/a29a9adb/docs/dev/table/streaming.md
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diff --git a/docs/dev/table/streaming.md b/docs/dev/table/streaming.md
index 9699507..d7d97fa 100644
--- a/docs/dev/table/streaming.md
+++ b/docs/dev/table/streaming.md
@@ -22,7 +22,7 @@ specific language governing permissions and limitations
under the License.
-->
-**TODO: has to be completely written**
+**TO BE DONE:** Intro
* This will be replaced by the TOC
{:toc}
@@ -30,6 +30,8 @@ under the License.
Dynamic table
-------------
+**TO BE DONE**
+
* Stream -> Table
* Table -> Stream
* update changes / retraction
@@ -39,17 +41,308 @@ Dynamic table
Time Attributes
---------------
-### Event-time
+Flink is able to process streaming data based on different notions of *time*.
-* DataStream: Timestamps & WMs required, `.rowtime` (replace attribute or extend schema)
-* TableSource: Timestamps & WMs & DefinedRowtimeAttribute
+- *Processing time* refers to the system time of the machine (also known as "wall-clock time") that is executing the respective operation.
+- *Event time* refers to the processing of streaming data based on timestamps which are attached to each row. The timestamps can encode when an event happened.
+- *Ingestion time* is the time that events enter Flink; internally, it is treated similarly to event time.
-{% top %}
+For more information about time handling in Flink, see the introduction about [Event Time and Watermarks]({{ site.baseurl }}/dev/event_time.html).
+
+Table programs require that the corresponding time characteristic has been specified for the streaming environment:
+
+<div class="codetabs" markdown="1">
+<div data-lang="java" markdown="1">
+{% highlight java %}
+final StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();
+
+env.setStreamTimeCharacteristic(TimeCharacteristic.ProcessingTime); // default
+
+// alternatively:
+// env.setStreamTimeCharacteristic(TimeCharacteristic.IngestionTime);
+// env.setStreamTimeCharacteristic(TimeCharacteristic.EventTime);
+{% endhighlight %}
+</div>
+<div data-lang="scala" markdown="1">
+{% highlight scala %}
+val env = StreamExecutionEnvironment.getExecutionEnvironment
+
+env.setStreamTimeCharacteristic(TimeCharacteristic.ProcessingTime) // default
+
+// alternatively:
+// env.setStreamTimeCharacteristic(TimeCharacteristic.IngestionTime)
+// env.setStreamTimeCharacteristic(TimeCharacteristic.EventTime)
+{% endhighlight %}
+</div>
+</div>
+
+Time-based operations such as windows in both the [Table API]({{ site.baseurl }}/dev/table/tableApi.html#windows) and [SQL]({{ site.baseurl }}/dev/table/sql.html#group-windows) require information about the notion of time and its origin. Therefore, tables can offer *logical time attributes* for indicating time and accessing corresponding timestamps in table programs.
+
+Time attributes can be part of every table schema. They are defined when creating a table from a `DataStream` or are pre-defined when using a `TableSource`. Once a time attribute has been defined at the beginning, it can be referenced as a field and can used in time-based operations.
+
+As long as a time attribute is not modified and is simply forwarded from one part of the query to another, it remains a valid time attribute. Time attributes behave like regular timestamps and can be accessed for calculations. If a time attribute is used in a calculation, it will be materialized and becomes a regular timestamp. Regular timestamps do not cooperate with Flink's time and watermarking system and thus can not be used for time-based operations anymore.
### Processing time
-* DataStream: `.proctime` (only extend schema)
-* TableSource: DefinedProctimeAttribute
+Processing time allows a table program to produce results based on the time of the local machine. It is the simplest notion of time but does not provide determinism. It neither requires timestamp extraction nor watermark generation.
+
+There are two ways to define a processing time attribute.
+
+#### During DataStream-to-Table Conversion
+
+The processing time attribute is defined with the `.proctime` property during schema definition. The time attribute must only extend the physical schema by an additional logical field. Thus, it can only be defined at the end of the schema definition.
+
+<div class="codetabs" markdown="1">
+<div data-lang="java" markdown="1">
+{% highlight java %}
+DataStream<Tuple2<String, String>> stream = ...;
+
+// declare an additional logical field as a processing time attribute
+Table table = tEnv.fromDataStream(stream, "Username, Data, UserActionTime.proctime");
+
+WindowedTable windowedTable = table.window(Tumble.over("10.minutes").on("UserActionTime").as("userActionWindow"));
+{% endhighlight %}
+</div>
+<div data-lang="scala" markdown="1">
+{% highlight scala %}
+val stream: DataStream[(String, String)] = ...
+
+// declare an additional logical field as a processing time attribute
+val table = tEnv.fromDataStream(stream, 'UserActionTimestamp, 'Username, 'Data, 'UserActionTime.proctime)
+
+val windowedTable = table.window(Tumble over 10.minutes on 'UserActionTime as 'userActionWindow)
+{% endhighlight %}
+</div>
+</div>
+
+#### Using a TableSource
+
+The processing time attribute is defined by a `TableSource` that implements the `DefinedProctimeAttribute` interface. The logical time attribute is appended to the physical schema defined by the return type of the `TableSource`.
+
+<div class="codetabs" markdown="1">
+<div data-lang="java" markdown="1">
+{% highlight java %}
+// define a table source with a processing attribute
+public class UserActionSource implements StreamTableSource<Row>, DefinedProctimeAttribute {
+
+ @Override
+ public TypeInformation<Row> getReturnType() {
+ String[] names = new String[] {"Username" , "Data"};
+ TypeInformation[] types = new TypeInformation[] {Types.STRING(), Types.STRING()};
+ return Types.ROW(names, types);
+ }
+
+ @Override
+ public DataStream<Row> getDataStream(StreamExecutionEnvironment execEnv) {
+ // create stream
+ DataStream<Row> stream = ...;
+ return stream;
+ }
+
+ @Override
+ public String getProctimeAttribute() {
+ // field with this name will be appended as a third field
+ return "UserActionTime";
+ }
+}
+
+// register table source
+tEnv.registerTableSource("UserActions", new UserActionSource());
+
+WindowedTable windowedTable = tEnv
+ .scan("UserActions")
+ .window(Tumble.over("10.minutes").on("UserActionTime").as("userActionWindow"));
+{% endhighlight %}
+</div>
+<div data-lang="scala" markdown="1">
+{% highlight scala %}
+// define a table source with a processing attribute
+class UserActionSource extends StreamTableSource[Row] with DefinedProctimeAttribute {
+
+ override def getReturnType = {
+ val names = Array[String]("Username" , "Data")
+ val types = Array[TypeInformation[_]](Types.STRING, Types.STRING)
+ Types.ROW(names, types)
+ }
+
+ override def getDataStream(execEnv: StreamExecutionEnvironment): DataStream[Row] = {
+ // create stream
+ val stream = ...
+ stream
+ }
+
+ override def getProctimeAttribute = {
+ // field with this name will be appended as a third field
+ "UserActionTime"
+ }
+}
+
+// register table source
+tEnv.registerTableSource("UserActions", new UserActionSource)
+
+val windowedTable = tEnv
+ .scan("UserActions")
+ .window(Tumble over 10.minutes on 'UserActionTime as 'userActionWindow)
+{% endhighlight %}
+</div>
+</div>
+
+### Event time
+
+Event time allows a table program to produce results based on the time that is contained in every record. This allows for consistent results even in case of out-of-order events or late events. It also ensures replayable results of the table program when reading records from persistent storage.
+
+Additionally, event time allows for unified syntax for table programs in both batch and streaming environments. A time attribute in a streaming environment can be a regular field of a record in a batch environment.
+
+In order to handle out-of-order events and distinguish between on-time and late events in streaming, Flink needs to extract timestamps from events and make some kind of progress in time (so-called [watermarks]({{ site.baseurl }}/dev/event_time.html)).
+
+An event time attribute can be defined either during DataStream-to-Table conversion or by using a TableSource.
+
+The Table API & SQL assume that in both cases timestamps and watermarks have been generated in the [underlying DataStream API]({{ site.baseurl }}/dev/event_timestamps_watermarks.html) before. Ideally, this happens within a `TableSource` with knowledge about the incoming data's characteristics and is hidden from the end user of the API.
+
+
+#### During DataStream-to-Table Conversion
+
+The event time attribute is defined with the `.rowtime` property during schema definition.
+
+Timestamps and watermarks must have been assigned in the `DataStream` that is converted.
+
+There are two ways of defining the time attribute when converting a `DataStream` into a `Table`:
+
+- Extending the physical schema by an additional logical field
+- Replacing a physical field by a logical field (e.g. because it is no longer needed after timestamp extraction).
+
+<div class="codetabs" markdown="1">
+<div data-lang="java" markdown="1">
+{% highlight java %}
+
+// Option 1:
+
+// extract timestamp and assign watermarks based on knowledge of the stream
+DataStream<Tuple3<String, String>> stream = inputStream.assignTimestampsAndWatermarks(...);
+
+// declare an additional logical field as an event time attribute
+Table table = tEnv.fromDataStream(stream, "Username, Data, UserActionTime.rowtime");
+
+
+// Option 2:
+
+// extract timestamp from first field, and assign watermarks based on knowledge of the stream
+DataStream<Tuple3<Long, String, String>> stream = inputStream.assignTimestampsAndWatermarks(...);
+
+// the first field has been used for timestamp extraction, and is no longer necessary
+// replace first field with a logical event time attribute
+Table table = tEnv.fromDataStream(stream, "UserActionTime.rowtime, Username, Data");
+
+// Usage:
+
+WindowedTable windowedTable = table.window(Tumble.over("10.minutes").on("UserActionTime").as("userActionWindow"));
+{% endhighlight %}
+</div>
+<div data-lang="scala" markdown="1">
+{% highlight scala %}
+
+// Option 1:
+
+// extract timestamp and assign watermarks based on knowledge of the stream
+val stream: DataStream[(String, String)] = inputStream.assignTimestampsAndWatermarks(...)
+
+// declare an additional logical field as an event time attribute
+val table = tEnv.fromDataStream(stream, 'Username, 'Data, 'UserActionTime.rowtime)
+
+
+// Option 2:
+
+// extract timestamp from first field, and assign watermarks based on knowledge of the stream
+val stream: DataStream[(Long, String, String)] = inputStream.assignTimestampsAndWatermarks(...)
+
+// the first field has been used for timestamp extraction, and is no longer necessary
+// replace first field with a logical event time attribute
+val table = tEnv.fromDataStream(stream, 'UserActionTime.rowtime, 'Username, 'Data)
+
+// Usage:
+
+val windowedTable = table.window(Tumble over 10.minutes on 'UserActionTime as 'userActionWindow)
+{% endhighlight %}
+</div>
+</div>
+
+#### Using a TableSource
+
+The event time attribute is defined by a `TableSource` that implements the `DefinedRowtimeAttribute` interface. The logical time attribute is appended to the physical schema defined by the return type of the `TableSource`.
+
+Timestamps and watermarks must be assigned in the stream that is returned by the `getDataStream()` method.
+
+<div class="codetabs" markdown="1">
+<div data-lang="java" markdown="1">
+{% highlight java %}
+// define a table source with a rowtime attribute
+public class UserActionSource implements StreamTableSource<Row>, DefinedRowtimeAttribute {
+
+ @Override
+ public TypeInformation<Row> getReturnType() {
+ String[] names = new String[] {"Username" , "Data"};
+ TypeInformation[] types = new TypeInformation[] {Types.STRING(), Types.STRING()};
+ return Types.ROW(names, types);
+ }
+
+ @Override
+ public DataStream<Row> getDataStream(StreamExecutionEnvironment execEnv) {
+ // create stream
+ // ...
+ // extract timestamp and assign watermarks based on knowledge of the stream
+ DataStream<Row> stream = inputStream.assignTimestampsAndWatermarks(...);
+ return stream;
+ }
+
+ @Override
+ public String getRowtimeAttribute() {
+ // field with this name will be appended as a third field
+ return "UserActionTime";
+ }
+}
+
+// register the table source
+tEnv.registerTableSource("UserActions", new UserActionSource());
+
+WindowedTable windowedTable = tEnv
+ .scan("UserActions")
+ .window(Tumble.over("10.minutes").on("UserActionTime").as("userActionWindow"));
+{% endhighlight %}
+</div>
+<div data-lang="scala" markdown="1">
+{% highlight scala %}
+// define a table source with a rowtime attribute
+class UserActionSource extends StreamTableSource[Row] with DefinedRowtimeAttribute {
+
+ override def getReturnType = {
+ val names = Array[String]("Username" , "Data")
+ val types = Array[TypeInformation[_]](Types.STRING, Types.STRING)
+ Types.ROW(names, types)
+ }
+
+ override def getDataStream(execEnv: StreamExecutionEnvironment): DataStream[Row] = {
+ // create stream
+ // ...
+ // extract timestamp and assign watermarks based on knowledge of the stream
+ val stream = inputStream.assignTimestampsAndWatermarks(...)
+ stream
+ }
+
+ override def getRowtimeAttribute = {
+ // field with this name will be appended as a third field
+ "UserActionTime"
+ }
+}
+
+// register the table source
+tEnv.registerTableSource("UserActions", new UserActionSource)
+
+val windowedTable = tEnv
+ .scan("UserActions")
+ .window(Tumble over 10.minutes on 'UserActionTime as 'userActionWindow)
+{% endhighlight %}
+</div>
+</div>
{% top %}
@@ -62,6 +355,8 @@ Flink's Table API and SQL interface use a `QueryConfig` to control the computati
### State Retention
+**TO BE DONE**
+
{% top %}