expxiaoli opened a new pull request #971:
URL: https://github.com/apache/orc/pull/971
…ng encoding columns
In old code, when dictionary string encoding columns are read by vectorized
reading, 2 copy of current stripe's dictionary data and 1 copy of next stripe's
dictionary data are hold in memory when reading across different stripes. That
could make vectorized reading's memory usage is larger than row reading. This
patch fixes this issue, and only hold 1 copy of current stripe's dictionary
data.
This patch logic has 3 parts:
1) Directly read data to primitive byte array, rather than using
DynamicByteArray as intermediate variable. Using DynamicByteArray as
intermediate variable causes 2 copy of current stripe's dictionary data are
hold in memory.
2) Lazy read dictionary data until read current batch data. In previous
code, RecordReaderImpl class's nextBatch method reads dictionary data of next
stripe through advanceToNextRow method, then memory will hold two stripe's
dictionary data. Through lazy read logic, only one stripe's dictionary data is
hold in memory when reading across different stripes.
3) Before lazy read dictionary data from current stripe, remove batch data's
reference to dictionary data from previous stripe. This could allow GC to clean
previous stripe's dictionary data memory.
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