Several fixes for writing large Arrow tables #57
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Fixes #56. The issue was the underlying flatbuffer array type was using an `UInt32` for the byte position where the flatbuffer array was located; in super large files, this overflowed. As this Array field is a Julia-side controlled type, we can easily switch to an Int64 to avoid this issue all together.
The bitpack encoding algorithm was allocating, which caused very large tables to slow down considerably with so much memory recycling. Rewriting it to avoid allocations leads to drastically fewer allocations and much faster writing performance. For non-optimized array writing, we also switch to writing to a buffer first to avoid hitting the global IO lock too much, which can also hurt performance on large files.
Just a few minor cleanups to ensure dictionary encoding types are consistent, and that variable names work correctly between writing first-time dictionary encodings and deltas.
Codecov Report
@@ Coverage Diff @@
## master #57 +/- ##
==========================================
- Coverage 83.34% 83.27% -0.07%
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Files 23 23
Lines 2642 2649 +7
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+ Hits 2202 2206 +4
- Misses 440 443 +3
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