TysonStanley commented on PR #43634:
URL: https://github.com/apache/arrow/pull/43634#issuecomment-2295015587
@jonkeane I'm late to adding this, but notably my a team member sent me
evidence that the index in data.table can cause problems in reading the parquet
back in (`Error: IOError: Couldn't deserialize thrift: TProtocolException:
Exceeded size limit`) and it explodes the size of the file (in her example from
400MB to 2GB with the only change being the index). See reprex below:
```r
library(data.table)
library(arrow)
dt<-data.table(x=c(1:1e8), y = round(runif(n=1:1e8, min=1, max=5)))
#Looking at rows where y == 3
dt[y == 3,]
#Creating a new variable, which is done uniformly across all rows
(suggesting the previous row index isn't applicable?)
dt[, z := 1]
#Save the dt
write_parquet(dt, "example.parquet")
gc()
#Cannot open the dt
dt_open<-read_parquet("example.parquet")
#Removing indexing that was created when looking at the y==3 subset before
saving allows
#the file to be opened after re-saving.
setindex(dt, NULL)
write_parquet(dt, "example2.parquet")
dt_open<-read_parquet("example2.parquet")
```
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