html_url,issue_url,id,node_id,user,created_at,updated_at,author_association,body,reactions,performed_via_github_app,issue
https://github.com/pydata/xarray/issues/2417#issuecomment-462422387,https://api.github.com/repos/pydata/xarray/issues/2417,462422387,MDEyOklzc3VlQ29tbWVudDQ2MjQyMjM4Nw==,10819524,2019-02-11T17:41:47Z,2019-02-11T17:41:47Z,CONTRIBUTOR,"Hi @jhamman, please excuse the lateness of this reply. It turned out that in the end all I needed to do was set `OMP_NUM_THREADS` to the number based on my cores I want to use (2 threads/core) before launching my processes. Thanks for the help and for keeping this open. Feel free to close this thread. ","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,361016974
https://github.com/pydata/xarray/issues/2417#issuecomment-422445732,https://api.github.com/repos/pydata/xarray/issues/2417,422445732,MDEyOklzc3VlQ29tbWVudDQyMjQ0NTczMg==,10819524,2018-09-18T15:44:03Z,2018-09-18T15:44:03Z,CONTRIBUTOR,"As per your suggestion, I retried with chunking and found a new error (due to the nature of my data having rotated poles, dask demanded that I save my data with astype(); this isn't my major concern so I'll deal with that somewhere else).

What I did notice was that when chunking was specified (`ds = xr.open_dataset(ncfile).chunking({'time': 10})`), I lost all parallelism and although I had specified different thread counts, the performance never crossed 110% (I imagine the extra 10% was due to I/O).

This is really a mystery and unfortunately, I haven't a clue how this beahviour is possible if parallel processing is disabled by default. The speed of my results when dask multprocessing isn't specified suggests that it must be using more processing power:

- using Multiprocessing calls to CDO with 5 ForkPoolWorkers = ~2h/5 files (100% x 5 CPUs)
- xarray without dask multiprocessing specifications = ~3min/5 files (spikes of 3500% on one CPU)

Could these spikes in CPU usage be due to other processes (e.g. memory usage, I/O)? ","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,361016974