• Hive,  I/O,  ORC,  S3,  Storage

    Simple Hive Queries with Predicates – Compressed Text vs ORC Files

    Usually source data come as compressed text files into Hadoop and we often run SQL queries on top of them without any transformations.

    Sometimes these queries are simple single-table search queries returning a few rows based on the specified predicates, and people often complain about their performance.

    Compressed Text Files

    Consider the following sample table:

    CREATE TABLE clicks
       id STRING, 
       name STRING,
       referral_id STRING
    LOCATION 's3://cloudsqale/hive/dmtolpeko.db/clicks/';

    In my case s3://cloudsqale/hive/dmtolpeko.db/clicks contains single file data.txt.gz that has 27.3M rows and relatively small size of 5.3 GB.

  • Amazon,  AWS,  I/O,  Logs,  S3,  Storage

    Collecting S3 Access Logs

    Amazon allows you to enable S3 access logging that you can use to monitor S3 performance: request rate, I/O workload, user and compute node level statistics, service delays and outages, and much more.

    S3 log files are quite small, uncompressed text files that in case of intensive S3 usage can be generated almost every second:

    2018-09-20 16:20:27     323567 2018-09-20-16-20-26-DE17FAE504462084
    2018-09-20 16:20:28     598192 2018-09-20-16-20-27-5F17C98DFA22DA31
    2018-09-20 16:20:29     618862 2018-09-20-16-20-28-4660E2CBCB0FB2C5
    2018-09-20 16:20:32     381675 2018-09-20-16-20-31-16549B7BABDA06AE
    2018-09-20 16:20:33     405131 2018-09-20-16-20-32-14AB46312C254397
    2018-09-20 16:20:34     587042 2018-09-20-16-20-33-385E799AFCEBAEE3
    2018-09-20 16:20:35     358275 2018-09-20-16-20-34-FA52E601A410E529
    2018-09-20 16:20:36     604080 2018-09-20-16-20-35-C02066EDF9026EF9

    So you can have 35K+ files generated per day (and there is no a sub-directory for each day), and if you are going to analyze S3 statistics for a long period of time (weeks, months), the performance of your Hive or Presto queries can be very low.

    Additionally there is often a lifecycle rule defined to keep logs only for 1-2 days.