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Commit 74049249 authored by Cheng Lian's avatar Cheng Lian Committed by Michael Armbrust
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[SPARK-3294][SQL] Eliminates boxing costs from in-memory columnar storage

This is a major refactoring of the in-memory columnar storage implementation, aims to eliminate boxing costs from critical paths (building/accessing column buffers) as much as possible. The basic idea is to refactor all major interfaces into a row-based form and use them together with `SpecificMutableRow`. The difficult part is how to adapt all compression schemes, esp. `RunLengthEncoding` and `DictionaryEncoding`, to this design. Since in-memory compression is disabled by default for now, and this PR should be strictly better than before no matter in-memory compression is enabled or not, maybe I'll finish that part in another PR.

**UPDATE** This PR also took the chance to optimize `HiveTableScan` by

1. leveraging `SpecificMutableRow` to avoid boxing cost, and
1. building specific `Writable` unwrapper functions a head of time to avoid per row pattern matching and branching costs.

TODO

- [x] Benchmark
- [ ] ~~Eliminate boxing costs in `RunLengthEncoding`~~ (left to future PRs)
- [ ] ~~Eliminate boxing costs in `DictionaryEncoding` (seems not easy to do without specializing `DictionaryEncoding` for every supported column type)~~  (left to future PRs)

## Micro benchmark

The benchmark uses a 10 million line CSV table consists of bytes, shorts, integers, longs, floats and doubles, measures the time to build the in-memory version of this table, and the time to scan the whole in-memory table.

Benchmark code can be found [here](https://gist.github.com/liancheng/fe70a148de82e77bd2c8#file-hivetablescanbenchmark-scala). Script used to generate the input table can be found [here](https://gist.github.com/liancheng/fe70a148de82e77bd2c8#file-tablegen-scala).

Speedup:

- Hive table scanning + column buffer building: **18.74%**

  The original benchmark uses 1K as in-memory batch size, when increased to 10K, it can be 28.32% faster.

- In-memory table scanning: **7.95%**

Before:

        | Building | Scanning
------- | -------- | --------
1       | 16472    | 525
2       | 16168    | 530
3       | 16386    | 529
4       | 16184    | 538
5       | 16209    | 521
Average | 16283.8  | 528.6

After:

        | Building | Scanning
------- | -------- | --------
1       | 13124    | 458
2       | 13260    | 529
3       | 12981    | 463
4       | 13214    | 483
5       | 13583    | 500
Average | 13232.4  | 486.6

Author: Cheng Lian <lian.cs.zju@gmail.com>

Closes #2327 from liancheng/prevent-boxing/unboxing and squashes the following commits:

4419fe4 [Cheng Lian] Addressing comments
e5d2cf2 [Cheng Lian] Bug fix: should call setNullAt when field value is null to avoid NPE
8b8552b [Cheng Lian] Only checks for partition batch pruning flag once
489f97b [Cheng Lian] Bug fix: TableReader.fillObject uses wrong ordinals
97bbc4e [Cheng Lian] Optimizes hive.TableReader by by providing specific Writable unwrappers a head of time
3dc1f94 [Cheng Lian] Minor changes to eliminate row object creation
5b39cb9 [Cheng Lian] Lowers log level of compression scheme details
f2a7890 [Cheng Lian] Use SpecificMutableRow in InMemoryColumnarTableScan to avoid boxing
9cf30b0 [Cheng Lian] Added row based ColumnType.append/extract
456c366 [Cheng Lian] Made compression decoder row based
edac3cd [Cheng Lian] Makes ColumnAccessor.extractSingle row based
8216936 [Cheng Lian] Removes boxing cost in IntDelta and LongDelta by providing specialized implementations
b70d519 [Cheng Lian] Made some in-memory columnar storage interfaces row-based
parent 184cd51c
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