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authorSeigneurin, Alexis (CONT) <Alexis.Seigneurin@capitalone.com>2017-03-30 16:12:17 +0100
committerSean Owen <sowen@cloudera.com>2017-03-30 16:12:17 +0100
commit669a11b61bc217a13217f1ef48d781329c45575e (patch)
treebd6052b109f987f51f88cd21ac31e67a138be646 /docs
parente9d268f63e7308486739aa56ece02815bfb432d6 (diff)
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[DOCS][MINOR] Fixed a few typos in the Structured Streaming documentation
Fixed a few typos. There is one more I'm not sure of: ``` Append mode uses watermark to drop old aggregation state. But the output of a windowed aggregation is delayed the late threshold specified in `withWatermark()` as by the modes semantics, rows can be added to the Result Table only once after they are ``` Not sure how to change `is delayed the late threshold`. Author: Seigneurin, Alexis (CONT) <Alexis.Seigneurin@capitalone.com> Closes #17443 from aseigneurin/typos.
Diffstat (limited to 'docs')
-rw-r--r--docs/structured-streaming-programming-guide.md18
1 files changed, 9 insertions, 9 deletions
diff --git a/docs/structured-streaming-programming-guide.md b/docs/structured-streaming-programming-guide.md
index ff07ad1194..b5cf9f1644 100644
--- a/docs/structured-streaming-programming-guide.md
+++ b/docs/structured-streaming-programming-guide.md
@@ -717,11 +717,11 @@ However, to run this query for days, it's necessary for the system to bound the
intermediate in-memory state it accumulates. This means the system needs to know when an old
aggregate can be dropped from the in-memory state because the application is not going to receive
late data for that aggregate any more. To enable this, in Spark 2.1, we have introduced
-**watermarking**, which let's the engine automatically track the current event time in the data and
+**watermarking**, which lets the engine automatically track the current event time in the data
and attempt to clean up old state accordingly. You can define the watermark of a query by
-specifying the event time column and the threshold on how late the data is expected be in terms of
+specifying the event time column and the threshold on how late the data is expected to be in terms of
event time. For a specific window starting at time `T`, the engine will maintain state and allow late
-data to be update the state until `(max event time seen by the engine - late threshold > T)`.
+data to update the state until `(max event time seen by the engine - late threshold > T)`.
In other words, late data within the threshold will be aggregated,
but data later than the threshold will be dropped. Let's understand this with an example. We can
easily define watermarking on the previous example using `withWatermark()` as shown below.
@@ -792,7 +792,7 @@ This watermark lets the engine maintain intermediate state for additional 10 min
data to be counted. For example, the data `(12:09, cat)` is out of order and late, and it falls in
windows `12:05 - 12:15` and `12:10 - 12:20`. Since, it is still ahead of the watermark `12:04` in
the trigger, the engine still maintains the intermediate counts as state and correctly updates the
-counts of the related windows. However, when the watermark is updated to 12:11, the intermediate
+counts of the related windows. However, when the watermark is updated to `12:11`, the intermediate
state for window `(12:00 - 12:10)` is cleared, and all subsequent data (e.g. `(12:04, donkey)`)
is considered "too late" and therefore ignored. Note that after every trigger,
the updated counts (i.e. purple rows) are written to sink as the trigger output, as dictated by
@@ -825,7 +825,7 @@ section for detailed explanation of the semantics of each output mode.
same column as the timestamp column used in the aggregate. For example,
`df.withWatermark("time", "1 min").groupBy("time2").count()` is invalid
in Append output mode, as watermark is defined on a different column
-as the aggregation column.
+from the aggregation column.
- `withWatermark` must be called before the aggregation for the watermark details to be used.
For example, `df.groupBy("time").count().withWatermark("time", "1 min")` is invalid in Append
@@ -909,7 +909,7 @@ track of all the data received in the stream. This is therefore fundamentally ha
efficiently.
## Starting Streaming Queries
-Once you have defined the final result DataFrame/Dataset, all that is left is for you start the streaming computation. To do that, you have to use the `DataStreamWriter`
+Once you have defined the final result DataFrame/Dataset, all that is left is for you to start the streaming computation. To do that, you have to use the `DataStreamWriter`
([Scala](api/scala/index.html#org.apache.spark.sql.streaming.DataStreamWriter)/[Java](api/java/org/apache/spark/sql/streaming/DataStreamWriter.html)/[Python](api/python/pyspark.sql.html#pyspark.sql.streaming.DataStreamWriter) docs)
returned through `Dataset.writeStream()`. You will have to specify one or more of the following in this interface.
@@ -1396,15 +1396,15 @@ You can directly get the current status and metrics of an active query using
`lastProgress()` returns a `StreamingQueryProgress` object
in [Scala](api/scala/index.html#org.apache.spark.sql.streaming.StreamingQueryProgress)
and [Java](api/java/org/apache/spark/sql/streaming/StreamingQueryProgress.html)
-and an dictionary with the same fields in Python. It has all the information about
+and a dictionary with the same fields in Python. It has all the information about
the progress made in the last trigger of the stream - what data was processed,
what were the processing rates, latencies, etc. There is also
`streamingQuery.recentProgress` which returns an array of last few progresses.
-In addition, `streamingQuery.status()` returns `StreamingQueryStatus` object
+In addition, `streamingQuery.status()` returns a `StreamingQueryStatus` object
in [Scala](api/scala/index.html#org.apache.spark.sql.streaming.StreamingQueryStatus)
and [Java](api/java/org/apache/spark/sql/streaming/StreamingQueryStatus.html)
-and an dictionary with the same fields in Python. It gives information about
+and a dictionary with the same fields in Python. It gives information about
what the query is immediately doing - is a trigger active, is data being processed, etc.
Here are a few examples.