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https://issues.apache.org/jira/browse/ARROW-16904?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Neal Richardson updated ARROW-16904:
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Summary: [C++] min/max not deterministic if Parquet files have multiple row
groups (was: dplyr summarise using min/max aggregate function
non-deterministic for large number of elements)
> [C++] min/max not deterministic if Parquet files have multiple row groups
> -------------------------------------------------------------------------
>
> Key: ARROW-16904
> URL: https://issues.apache.org/jira/browse/ARROW-16904
> Project: Apache Arrow
> Issue Type: Bug
> Components: R
> Affects Versions: 8.0.0
> Environment: $ lsb_release -a
> No LSB modules are available.
> Distributor ID: Ubuntu
> Description: Ubuntu 20.04.4 LTS
> Release: 20.04
> Codename: focal
> Reporter: Robert On
> Priority: Critical
>
>
> The following code produces non-deterministic result for getting the minimum
> value of a sequence of 1e6 integers.
> {code:java}
> sapply(1:100, function(x) {
> # create parquet file with a val column with numbers 1 to 100,000
> arrow::write_parquet(
> data.frame(val = 1:1e5), "test.parquet")
> arrow::open_dataset("test.parquet") %>%
> dplyr::summarise(min_val = min(val)) %>%
> dplyr::collect() %>% dplyr::pull(min_val)
> }) %>% table()
> sapply(1:100, function(x) {
> # create parquet file with a val column with numbers 1 to 1,000,000
> arrow::write_parquet(
> data.frame(val = 1:1e6), "test.parquet")
>
> arrow::open_dataset("test.parquet") %>%
> dplyr::summarise(min_val = min(val)) %>%
> dplyr::collect() %>% dplyr::pull(min_val)
> }) %>% table()
> {code}
> The first 100 simulations using numbers 1 to 1e5 is able to find the minimum
> number (1) all 100 times.
> The second 100 simulations using numbers 1 to 1e6 only finds the minimum
> number (1) 65 out of 100 times. It finds near multiples of 131073, 25, 8, and
> 2 times respectively.
> {code:java}
> . 1
> 100
> . 1 131073 262145 393217
> 65 25 8 2 {code}
>
>
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