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ASF GitHub Bot commented on PARQUET-2149: ----------------------------------------- parthchandra commented on PR #968: URL: https://github.com/apache/parquet-mr/pull/968#issuecomment-1136552664 > This is interesting, because when I did profiling of Trino, I found that although I/O (from S3, over the network no less) was significant, even more time was spent in compute. Maybe you're getting improved performance because you're increasing _parallelism_ between I/O and compute. It may be because I was using Spark's vectorized parquet decoding which is an order or magnitude faster than parquet library's row by row decoding (see [Spark benchmarks](https://github.com/apache/spark/blob/master/sql/core/benchmarks/DataSourceReadBenchmark-results.txt)). If trino is not doing vectorized decoding (I took a very quick look and I don't think it is), I would suggest you can look into that next. All the cool kids are doing it. > Implement async IO for Parquet file reader > ------------------------------------------ > > Key: PARQUET-2149 > URL: https://issues.apache.org/jira/browse/PARQUET-2149 > Project: Parquet > Issue Type: Improvement > Components: parquet-mr > Reporter: Parth Chandra > Priority: Major > > ParquetFileReader's implementation has the following flow (simplified) - > - For every column -> Read from storage in 8MB blocks -> Read all > uncompressed pages into output queue > - From output queues -> (downstream ) decompression + decoding > This flow is serialized, which means that downstream threads are blocked > until the data has been read. Because a large part of the time spent is > waiting for data from storage, threads are idle and CPU utilization is really > low. > There is no reason why this cannot be made asynchronous _and_ parallel. So > For Column _i_ -> reading one chunk until end, from storage -> intermediate > output queue -> read one uncompressed page until end -> output queue -> > (downstream ) decompression + decoding > Note that this can be made completely self contained in ParquetFileReader and > downstream implementations like Iceberg and Spark will automatically be able > to take advantage without code change as long as the ParquetFileReader apis > are not changed. > In past work with async io [Drill - async page reader > |https://github.com/apache/drill/blob/master/exec/java-exec/src/main/java/org/apache/drill/exec/store/parquet/columnreaders/AsyncPageReader.java] > , I have seen 2x-3x improvement in reading speed for Parquet files. -- This message was sent by Atlassian Jira (v8.20.7#820007)