### What changes were proposed in this pull request?
The idea is to improve the performance of HybridStore by adding batch write support to LevelDB. #28412 introduces HybridStore. HybridStore will write data to InMemoryStore at first and use a background thread to dump data to LevelDB once the writing to InMemoryStore is completed. In the comments section of #28412 , mridulm mentioned using batch writing can improve the performance of this dumping process and he wrote the code of writeAll().
### Why are the changes needed?
I did the comparison of the HybridStore switching time between one-by-one write and batch write on an HDD disk. When the disk is free, the batch-write has around 25% improvement, and when the disk is 100% busy, the batch-write has 7x - 10x improvement.
when the disk is at 0% utilization:
| log size, jobs and tasks per job | original switching time, with write() | switching time with writeAll() |
| ---------------------------------- | ------------------------------------- | ------------------------------ |
| 133m, 400 jobs, 100 tasks per job | 16s | 13s |
| 265m, 400 jobs, 200 tasks per job | 30s | 23s |
| 1.3g, 1000 jobs, 400 tasks per job | 136s | 108s |
when the disk is at 100% utilization:
| log size, jobs and tasks per job | original switching time, with write() | switching time with writeAll() |
| --------------------------------- | ------------------------------------- | ------------------------------ |
| 133m, 400 jobs, 100 tasks per job | 116s | 17s |
| 265m, 400 jobs, 200 tasks per job | 251s | 26s |
I also ran some write related benchmarking tests on LevelDBBenchmark.java and measured the total time of writing 1024 objects. The tests were conducted when the disk is at 0% utilization.
| Benchmark test | with write(), ms | with writeAll(), ms |
| ------------------------ | ---------------- | ------------------- |
| randomUpdatesIndexed | 213.06 | 157.356 |
| randomUpdatesNoIndex | 57.869 | 35.439 |
| randomWritesIndexed | 298.854 | 229.274 |
| randomWritesNoIndex | 66.764 | 38.361 |
| sequentialUpdatesIndexed | 87.019 | 56.219 |
| sequentialUpdatesNoIndex | 61.851 | 41.942 |
| sequentialWritesIndexed | 94.044 | 56.534 |
| sequentialWritesNoIndex | 118.345 | 66.483 |
### Does this PR introduce _any_ user-facing change?
No
### How was this patch tested?
Manually tested.
Closes#29149 from baohe-zhang/SPARK-32350.
Authored-by: Baohe Zhang <baohe.zhang@verizonmedia.com>
Signed-off-by: Jungtaek Lim (HeartSaVioR) <kabhwan.opensource@gmail.com>
7b9d7551a6