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/1396#issuecomment-383477976,https://api.github.com/repos/pydata/xarray/issues/1396,383477976,MDEyOklzc3VlQ29tbWVudDM4MzQ3Nzk3Ng==,35775735,2018-04-23T07:18:23Z,2019-01-13T06:32:12Z,NONE,"I am using MITgcm and want to incorporate my latitude and longitude information from my grid file to state file. Could you please help me in this regard?
","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,225774140
https://github.com/pydata/xarray/issues/1396#issuecomment-306850272,https://api.github.com/repos/pydata/xarray/issues/1396,306850272,MDEyOklzc3VlQ29tbWVudDMwNjg1MDI3Mg==,9655353,2017-06-07T16:30:04Z,2017-06-07T16:50:40Z,NONE,"That's great to know! I think there's no need to try my 'solution' then, maybe only out of pure interest.

It would of course be interesting to know why a 'custom' chunked dataset was apparently not affected by the bug. And if it was indeed the case.

EDIT: I read the discussion on dask github and the xarray mailinglist. It's probably because when explicit chunking is used, the chunks are not aliased and fusing works as expected.","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,225774140
https://github.com/pydata/xarray/issues/1396#issuecomment-306838587,https://api.github.com/repos/pydata/xarray/issues/1396,306838587,MDEyOklzc3VlQ29tbWVudDMwNjgzODU4Nw==,9655353,2017-06-07T15:51:34Z,2017-06-07T15:53:06Z,NONE,"We had similar performance issues with xarray+dask, which we solved by using a chunking heuristic when opening a dataset. You can read about it in #1440. Now, in our case the data really wouldn't fit in memory, which is clearly not the case in your gist. Anyway, I thought I'd play around with your gist and see if chunking can make a difference.

I couldn't use your example directly, as the data it generates in memory is too large for the dev VM I'm on with this. So I changed the generated file size to (12, 1000, 2000), the essence of your gist remained though, it would take ~25 seconds to do the time series extraction, whereas ~800 ms using ```extract_point_xarray()```.

So, I thought I'd try our 'chunking heuristic' on the generated test datasets. Simply split the dataset in 2x2 chunks along spatial dimensions. So:

```python
ds = xr.open_mfdataset(all_files, decode_cf=False, chunks={'time':12, 'x':1000, 'y':500})
```

To my surprise:
```python
# time extracting a timeseries of a single point
y, x = 200, 300
with ProgressBar():
    %time ts = ds.data[:, y, x].load()
```
results in
```
[########################################] | 100% Completed |  0.7s
CPU times: user 124 ms, sys: 268 ms, total: 392 ms
Wall time: 826 ms
```

I'm not entirely sure what's happening, as the file obviously fits in memory just fine because the looping thing works well. Maybe it's fine when you loop through them one by one, but the single file chunk turns out to be too large when dask wants to parallelize the whole thing. I really have no idea.

I'd be very intrigued to see if you can get a similar result by doing a simple 2x2xtime chunking. By the way, ```chunks={'x':1000, 'y':500, 'time':1}``` produces similar results with some overhead. Extraction took ~1.5 seconds. 

EDIT:
```python
print(xr.__version__)
print(dask.__version__)
```
```
0.9.5
0.14.1
```","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,225774140