Frankly speaking I do not care about EXACTLY ONCE... I am OK with ATLEAST ONCE
at long as system does not fail every 5 to 7 days with no recovery option.
On Wednesday, June 17, 2020, 02:31:50 PM PDT, Rachana Srivastava
<[email protected]> wrote:
Thanks so much TD. Thanks for forwarding your datalake project but at this
time we have budget constraints we can only use open source project.
I just want the Structured Streaming Application or Spark Streaming DStream
Application to run without and issue for a long time.. I do not want the size
of metadata to grow too large that we start getting these OOM issues. The only
way to resolve this OOM issues is by deleting the checkpoint and metadata
folders. That means loosing customer data. We have 60 seconds batch where we
are coleasing and returning only one file per partition. So we do not have
small file issues also...
What do you suggest? How should we resolve this issue?
We have very simple 5 line program that reads data from Kafka and output data
to S3. 1. Reading records from Kafka topic
Dataset<Row> inputDf = spark \
.readStream \
.format("kafka") \
.option("kafka.bootstrap.servers", "host1:port1,host2:port2") \
.option("subscribe", "topic1") \
.option("startingOffsets", "earliest") \
.load()
2. Use from_json API from Spark to extract your data for further transformation
in a dataset.
Dataset<Row> dataDf = inputDf.select(from_json(col("value").cast("string"),
EVENT_SCHEMA).alias("event"))
....withColumn("oem_id", col("metadata.oem_id"));
3. Construct a temp table of above dataset using SQLContext
SQLContext sqlContext = new SQLContext(sparkSession);
dataDf.createOrReplaceTempView("event");
4. Flatten events since Parquet does not support hierarachical data.
5. Store output in parquet format on S3
StreamingQuery query = flatDf.writeStream().format("parquet")
On Wednesday, June 17, 2020, 02:02:20 PM PDT, Jungtaek Lim
<[email protected]> wrote:
Just in case if anyone prefers ASF projects then there are other alternative
projects in ASF as well, alphabetically, Apache Hudi [1] and Apache Iceberg
[2]. Both are recently graduated as top level projects. (DISCLAIMER: I'm not
involved in both.)
BTW it would be nice if we make the metadata implementation on file stream
source/sink be pluggable - from what I've seen, plugin approach has been
selected as the way to go whenever some part is going to be complicated and it
becomes arguable whether the part should be handled in Spark project vs should
be outside. e.g. checkpoint manager, state store provider, etc. It would open
up chances for the ecosystem to play with the challenge "without completely
re-writing the file stream source and sink", focusing on scalability for
metadata in a long run query. Alternative projects described above will still
provide more higher-level features and look attractive, but sometimes it may be
just "using a sledgehammer to crack a nut".
1. https://hudi.apache.org/2. https://iceberg.apache.org/
On Thu, Jun 18, 2020 at 2:34 AM Tathagata Das <[email protected]>
wrote:
Hello Rachana,
Getting exactly-once semantics on files and making it scale to a very large
number of files are very hard problems to solve. While Structured Streaming +
built-in file sink solves the exactly-once guarantee that DStreams could not,
it is definitely limited in other ways (scaling in terms of files, combining
batch and streaming writes in the same place, etc). And solving this problem
requires a holistic solution that is arguably beyond the scope of the Spark
project.
There are other projects that are trying to solve this file management issue.
For example, Delta Lake (full disclosure, I am involved in it) was built to
exactly solve this problem - get exactly-once and ACID guarantees on files, but
also scale to handling millions of files. Please consider it as part of your
solution.
On Wed, Jun 17, 2020 at 9:50 AM Rachana Srivastava
<[email protected]> wrote:
I have written a simple spark structured steaming app to move data from Kafka
to S3. Found that in order to support exactly-once guarantee spark creates
_spark_metadata folder, which ends up growing too large as the streaming app is
SUPPOSE TO run FOREVER. But when the streaming app runs for a long time the
metadata folder grows so big that we start getting OOM errors. Only way to
resolve OOM is delete Checkpoint and Metadata folder and loose VALUABLE
customer data.
Spark open JIRAs SPARK-24295 and SPARK-29995, SPARK-30462, and SPARK-24295)
Since Spark Streaming was NOT broken like this. Is Spark Streaming a BETTER
choice?
