issue_comments: 224049602

@mangecoeur, although it's not an xarray-based solution, I've found that by far the best solution to this problem is to transform your dataset from the "timeslice" format (which is convenient for models to write out - all the data at a given point in time, often in separate files for each time step) to "timeseries" format - a continuous format, where you have all the data for a single variable in a single (or much smaller collection of) files.

NCAR published a great utility for converting batches of NetCDF output from timeslice to timeseries format here; it's significantly faster than any shell-script/CDO/NCO solution I've ever encountered, and it parallelizes extremely easily.

Adding a simple post-processing step to convert my simulation output to timeseries format dramatically reduced my overall work time. Before, I had a separate handler which re-implemented open_mfdataset(), performed an intermediate reduction (usually extracting a variable), and then concatenated within xarray. This could get around the open file limit, but it wasn't fast. My pre-processed data is often still big - barely fitting within memory - but it's far easier to handle, and you can throw dask at it no problem to get huge speedups in analysis.