Improvements to buffered reading for parquet #5611
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malhotrashivam
added
parquet
rcaudy
reviewed
Jun 14, 2024
Util/channel/src/main/java/io/deephaven/util/channel/SeekableChannelsProvider.java
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Util/channel/src/main/java/io/deephaven/util/channel/SeekableChannelsProvider.java
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...dfile/src/main/java/io/deephaven/extensions/trackedfile/TrackedSeekableChannelsProvider.java
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...dfile/src/main/java/io/deephaven/extensions/trackedfile/TrackedSeekableChannelsProvider.java
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...mpression/src/main/java/io/deephaven/parquet/compress/DeephavenCompressorAdapterFactory.java
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extensions/parquet/base/src/main/java/io/deephaven/parquet/base/ColumnChunkReaderImpl.java
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malhotrashivam
commented
Jun 14, 2024
| private Dictionary readDictionary(long dictionaryPageOffset, SeekableChannelContext channelContext) { | ||
| // Use the context object provided by the caller, or create (and close) a new one | ||
| try ( | ||
| final ContextHolder holder = SeekableChannelContext.ensureContext(channelsProvider, channelContext); |
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In the original code, we used to make the channel and stream in the calling method and this method would just use the same stream and not touch the underlying channel.
Now we make two streams, one for header and one for data. And we use the same channel.
Note that the channel's position gets updated after reading the header.
So I wanted to make the channel's lifecycle limited to this method so that no one else should depend on or use this channel. That is why I moved the logic for making the channel inside this method.
malhotrashivam
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rcaudy
reviewed
Jun 14, 2024
Util/channel/src/main/java/io/deephaven/util/channel/SeekableChannelsProvider.java
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rcaudy
approved these changes
Jun 15, 2024
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Currently, while reading bytes from parquet files, we read in chunks of 8K bytes.
So for cases, where we need fewer bytes (like reading page headers), this leads to extra bytes read.
And for cases where we need to read bulk of data (like reading actual data bytes), this can lead to repeated reads in 8k chunks, till we get the required number of bytes.
This PR adds a size hint to the stream creation method, so that we can accurately created an internal buffered input stream based on how much data the user actually want to read from the stream.
This PR leads to minor parquet read performance improvements.