Weston Pace created ARROW-16452:
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Summary: [R] After dataset scan, some RAM is left consumed until a
garbage collection pass
Key: ARROW-16452
URL: https://issues.apache.org/jira/browse/ARROW-16452
Project: Apache Arrow
Issue Type: Improvement
Components: R
Reporter: Weston Pace
This might be "not a bug" but I wonder if we can do something better here.
When I create and execute a dplyr query there is a bunch of RAM that is left
allocated until the next GC pass.
Since R's garbage collection is only based on RAM that R has allocated this
extra memory (which can be quite substantial) might never be freed.
Perhaps we should just manually trigger a gc pass after running an execution
plan? Or it may be good to get a better understanding of what exactly this
memory is being used for.
In the example below I load ~2GB of data but after the collect there is ~3GB
used. I wait 10 seconds to ensure it's not jemalloc. Then I run {{gc()}}
manually and ~1GB is freed.
{noformat}
> dataset = arrow::open_dataset('/home/pace/dev/data/dataset/parquet/5')
> default_memory_pool()$bytes_allocated
[1] 64
> x <- dataset %>% collect(as_data_frame=FALSE)
> arrow::default_memory_pool()$bytes_allocated
> Sys.sleep(10)
> arrow::default_memory_pool()$bytes_allocated
[1] 2921135104
> gc()
used (Mb) gc trigger (Mb) max used (Mb)
Ncells 917099 49.0 1498168 80.1 1498168 80.1
Vcells 1649894 12.6 8388608 64.0 2617403 20.0
> arrow::default_memory_pool()$bytes_allocated
[1] 2028716480
{noformat}
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