• Amazon,  AWS,  EMR,  S3,  Spark

    Amazon EMR Spark – Ignoring Partition Filter and Listing All Partitions When Reading from S3A

    April 20, 2022

    I have a partitioned Hive table created by an open-source version of Hadoop that uses S3A scheme as the location for every partition. The table has more than 10,000 partitions and every partition has about 8,000 Parquet files:

    $ hive -e "show partitions events";
...
dateint=20220419/hour=11
dateint=20220419/hour=12
dateint=20220419/hour=13

$ hive -e "describe formatted events partition (dateint=20220419, hour='11')" | grep Location
Location:   s3a://cloudsqale/events/dateint=20220419/hour=11

$ hive -e "describe formatted events partition (dateint=20220419, hour='12')" | grep Location
Location:   s3a://cloudsqale/events/dateint=20220419/hour=12

$ hive -e "describe formatted events partition (dateint=20220419, hour='13')" | grep Location
Location:   s3a://cloudsqale/events/dateint=20220419/hour=13

    S3A:// is specified for every partition in this table.

    Reading a Partition in Amazon EMR Spark

    When I made an attempt to read data from a single partition using Spark SQL:

    $ spark-sql --master yarn -e "select count(*) from events where dateint=20220419 and hour='11'"

    The Spark driver failed with:

    # java.lang.OutOfMemoryError: GC overhead limit exceeded
# -XX:OnOutOfMemoryError="kill -9 %p"
#   Executing /bin/sh -c "kill -9 4847"...
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  • AWS,  Flink,  S3

    Flink and S3 Entropy Injection for Checkpoints

    January 2, 2021

    When you use S3 for storing checkpoints it can easily become a bottleneck especially for your Flink application with a lot of subtasks. To overcome this problem FLINK-9061 introduced an entropy ingestion to the checkpoint path.

    But the Flink documentation provides a misleading example (at least up to Flink 1.13) that actually destroys the value of the checkpoint entropy.

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  • AWS,  S3

    S3 Multipart Upload – 5 MB Part Size Limit

    May 27, 2020

    It is a well known limitation that Amazon S3 multipart upload requires the part size to be between 5 MB and 5 GB with an exception that the last part can be less than 5 MB.

    Does it mean that you cannot upload a single small file (< 5 MB) to S3 using the multipart upload?

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  • AWS,  Hive,  S3

    Hive Table for S3 Access Logs

    May 26, 2020

    Although Amazon S3 can generate a lot of logs and it makes sense to have an ETL process to parse, combine and put the logs into Parquet or ORC format for better query performance, there is still an easy way to analyze logs using a Hive table created just on top of the raw S3 log directory.

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  • AWS,  I/O,  S3

    S3 Multipart Upload – S3 Access Log Messages

    April 17, 2020

    Most applications writing data into S3 use the S3 multipart upload API to upload data in parts. First, you initiate the load, then upload parts and finally complete the multipart upload.

    Let’s see how this operation is reflected in the S3 access log. My application uploaded the file data.gz into S3, and I can view it as follows:

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