Q :
"Is there an effective way that enables to read those csv files effectively ... ?"
A :
Oh, sure, there is :
CSV format ( standard attempts in RFC4180 ) is not unambiguous and is not obeyed under all circumstances ( commas inside fields, header present or not ), so some caution & care is needed here. Given you are your own data curator, you shall be able to decide plausible steps for handling your own data properly.
So, the as-is state is :
# in <_folder_1_>
:::::::: # 8000 CSV-files ~ 2GB in total
||||||||||||||||||||||||||||||||||||||||||| # 8000 CSV-files ~ 200GB in total
# in <_folder_2_>
Speaking efficiency, O/S coreutils provide the best, stable, proven and most efficient (as system tool used to be since ever ) tools for the phase of merging thousands and thousands of plain CSV-files' content :
###################### if need be,
###################### use an in-place remove of all CSV-file headers first :
for F in $( ls *.csv ); do sed -i '1d' $F; done
this helps for case we cannot avoid headers on the CSV-exporter side. Works like this :
(base):~$ cat ?.csv
HEADER
1
2
3
HEADER
4
5
6
HEADER
7
8
9
(base):~$ for i in $( ls ?.csv ); do sed -i '1d' $i; done
(base):~$ cat ?.csv
1
2
3
4
5
6
7
8
9
Now, the merging phase :
###################### join
cat *.csv > __all_CSVs_JOINED.csv
Given the nature of the said file storage policy, performance can be boosted by using more processes for independent taking small files and large files separately, as defined above, having put the logic inside a pair of conversion_script_?.sh shell-scripts :
parallel --jobs 2 conversion_script_{1}.sh ::: $( seq -f "%1g" 1 2 )
As the transformation is a "just"-[CONCURRENT] flow of processing for a sake of removing the CSV-headers, but a pure-[SERIAL] ( for larger number of files, there might become interesting to use a multi-staged tree of trees - using several stages of [SERIAL]-collections of [CONCURRENT]-ly pre-processed leaves, yet for just 8000 files, not knowing the actual file-system details, the latency-masking from a just-[CONCURRENT] processing both of the directories just independently will be fine to start with )
Last but not least, the final pair of ___all_CSVs_JOINED.csv are safe to get opened using in a way, that prevents moving all disk-stored date into RAM at once ( using chunk-size-fused file-reading-iterator, avoiding RAM-spillovers by using mmaped-mode as a context manager ) :
with pandas.read_csv( "<_folder_1_>//___all_CSVs_JOINED.csv",
sep = NoDefault.no_default,
delimiter = None,
...
chunksize = SAFE_CHUNK_SIZE,
...
memory_map = True,
...
) \
as df_reader_MMAPer_CtxMGR:
...
When tweaking for ultimate performance, details matter and depend on physical hardware bottlenecks ( disk-I/O-wise, filesystem-wise, RAM-I/O-wise ), so due care may take further improvement for minimising the repetitive performed end-to-end processing times ( sometimes even turning data into a compressed/zipped form, in cases, where CPU/RAM resources permit sufficient performance advantages over limited performance of disk-I/O throughput - moving less bytes is so faster, that CPU/RAM-decompression costs are still lower, than moving 200+ [GB]s of uncompressed plain text data.
Details matter,
tweak options,
benchmark,
tweak options,
benchmark,
tweak options,
benchmark
would be nice to post your progress on testing the performance
end-2-end duration of strategy ... [s] AS-IS now
end-2-end duration of strategy ... [s] with parallel --jobs 2 ...
end-2-end duration of strategy ... [s] with parallel --jobs 4 ...
end-2-end duration of strategy ... [s] with parallel --jobs N ... + compression
... keep us posted
