[General/Parallel] Cores hang when calling mcapply

Hi Posit users.

Apologies for the lack of tags because not really sure where to put this one.

I multiple, VERY large dataset for which I need to generate 0/1 absence/presence columns
Some include over 200M rows, with two columns that need presence/absence columns based on the strings contained within them, as an example, one set has ~29k unique values and the other with ~15k unique values (no overlap across the two).

Using a combination of custom functions:

crewjanitormakeclean <- function(df,columns) {
  df <- df |> mutate(across(columns, ~make_clean_names(.,  allow_dupes = TRUE)))
  return(df)
}
  
mass_pivot_wider <- function(df,column,prefix) {
  df <- df |> distinct() |> mutate(n = 1) |> pivot_wider(names_from = glue("{column}"), values_from = n, names_prefix = prefix, values_fill = list(n = 0))
  return(df)
}
  
sum_group_function <- function(df) {
  df <- df |> group_by(ID_Key) |> summarise(across(c(starts_with("column1_name_"),starts_with("column2_name_"),), ~ sum(.x, na.rm = TRUE))) |> ungroup()
  return(df)
}

and splitting up the data into a list of 110k individual dataframes based on Key_ID

temp <-
  open_dataset(
    sources = input_files,
    format = 'csv',
    unify_schema = TRUE,
    col_types = schema(
      "ID_Key" = string(),
      "column1" = string(),
      "column1" = string()
    )
  ) |> as_tibble()
    

  keeptabs <- split(temp, temp$ID_Key)

I used a multicore framework to distribute the sum functions across each Key_ID when a multicore argument is enabled.

	
    if(isTRUE(multicore)){
      output <- mclapply(1:length(modtabs), function(i) crewjanitormakeclean(modtabs[[i]],c("string_columns_2","string_columns_1")), mc.cores = numcores)
      output <- mclapply(1:length(modtabs), function(i) mass_pivot_wider(modtabs[[i]],"string_columns_1","col_1_name_"), mc.cores = numcores)
      output <- mclapply(1:length(modtabs), function(i) mass_pivot_wider(modtabs[[i]],"string_columns_2","col_2_name_"), mc.cores = numcores)
    }else{
      output <- lapply(1:length(modtabs), function(i) crewjanitormakeclean(modtabs[[i]],c("string_columns_2","string_columns_1")))
      output <- lapply(1:length(modtabs), function(i) mass_pivot_wider(modtabs[[i]],"string_columns_1","col_1_name_"))
      output <- mclapply(1:length(modtabs), function(i) mass_pivot_wider(modtabs[[i]],"string_columns_2","col_2_name_"))
    }

Moving every Key_ID to a single row and then row-binding the data while creating new columns for the differences across Key_IDs from the pivot using the following solution (78 upvotes at time of post):

  allNms <- unique(unlist(lapply(keeptabs, names)))
  
  output <- do.call(rbind,
                     c(lapply(keeptabs,
                              function(x) data.frame(c((x), sapply(setdiff(allNms, names(x)),
                                                                 function(y) NA))) |> as_tibble()),
                       make.row.names=FALSE)) |> mutate(across(c(starts_with("column1_name_"), starts_with("column2_name_")), coalesce, 0))

However, I have noticed that the jobs seem to "hang" after a while, with the initial 30 or so (numcores == 30 in the workflow, equal to the number of cores I reserved) at 100% of the requested CPU, and then several "zombie" processes occur and the cores just stop at 0% and never proceed, usually dying with a timeout or not all jobs running to completion failure to join of some kind.

This happens in both base R and RStudio, and I haven't been able to figure out if it's something wrong with the code, the size of the data, or our architecture, but I would appreciate any suggestions as to what I might be able to do about this.

Before they are suggested, I have also tried this same approach with foreach, snow, and the future, and furr and base parallel with mc.apply seems to be the only thing that works for at least one dataset.

In the event it has something to do with our architecture, here is what we are running on and our loaded packages:

NAME="Red Hat Enterprise Linux"
VERSION="9.3 (Plow)"
ID="rhel"
ID_LIKE="fedora"
VERSION_ID="9.3"
PLATFORM_ID="platform:el9"
PRETTY_NAME="Red Hat Enterprise Linux 9.3 (Plow)"
ANSI_COLOR="0;31"
LOGO="fedora-logo-icon"
CPE_NAME="cpe:/o:redhat:enterprise_linux:9::baseos"
HOME_URL="https://www.redhat.com/"
DOCUMENTATION_URL="https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/9"
BUG_REPORT_URL="https://bugzilla.redhat.com/"
REDHAT_BUGZILLA_PRODUCT="Red Hat Enterprise Linux 9"
REDHAT_BUGZILLA_PRODUCT_VERSION=9.3
REDHAT_SUPPORT_PRODUCT="Red Hat Enterprise Linux"
REDHAT_SUPPORT_PRODUCT_VERSION="9.3"
Operating System: Red Hat Enterprise Linux 9.3 (Plow)
    CPE OS Name: cpe:/o:redhat:enterprise_linux:9::baseos
         Kernel: Linux 5.14.0-362.13.1.el9_3.x86_64
   Architecture: x86-64
Hardware Vendor: Dell Inc.
 Hardware Model: PowerEdge R840
Firmware Version: 2.15.1

R Version:
R.Version()
$platform
[1] "x86_64-pc-linux-gnu"
$arch
[1] "x86_64"
$os
[1] "linux-gnu"
$system
[1] "x86_64, linux-gnu"
$status
[1] ""
$major
[1] "4"
$minor
[1] "3.2"
$year
[1] "2023"
$month
[1] "10"
$day
[1] "31"
$`svn rev`
[1] "85441"
$language
[1] "R"
$version.string
[1] "R version 4.3.2 (2023-10-31)"
$nickname
[1] "Eye Holes"

RStudio Server Version:
RStudio 2023.09.1+494 "Desert Sunflower" Release (cd7011dce393115d3a7c3db799dda4b1c7e88711, 2023-10-16) for RHEL 9
Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/130.0.0.0 Safari/537.36

PPM Repo:
https://packagemanager.posit.co/cran/__linux__/rhel9/latest

attached base packages:
[1] parallel  stats     graphics  grDevices datasets  utils     methods   base     

other attached packages:
[1] listenv_0.9.1        microbenchmark_1.5.0 dbplyr_2.4.0         duckplyr_0.4.1       readxl_1.4.3         fastDummies_1.7.3   
[7] glue_1.8.0           arrow_14.0.2.1       data.table_1.15.2    toolbox_0.1.1        janitor_2.2.0        lubridate_1.9.3     
[13] forcats_1.0.0        stringr_1.5.1        dplyr_1.1.4          purrr_1.0.2          readr_2.1.5          tidyr_1.3.1         
[19] tibble_3.2.1         ggplot2_3.5.0        tidyverse_2.0.0      duckdb_1.1.2         DBI_1.2.3            fs_1.6.3 

Happy to provide additional information if it would be helpful.

Thank you in advance!