What happened: I've been using xarray to open zarr datasets within a Flask app, and spent some time debugging a memory leak. What I found is that open_zarr() defaults to chunks='auto', rather than chunks=None which is the default for open_dataset(). The result is that open_zarr() ends up calling _maybe_chunk() on the dataset's variables by default.

For whatever reason this function is generating dask items that are not easily cleared from memory within the context of a Flask route, and memory usage continues to grow within my app, at least towards some plateau. This memory growth isn't reproducible outside of a Flask route, so it's a bit of a niche problem.

First proposal would be to simply align the default chunks argument between open_zarr() and open_dataset(). I'm happy to submit a PR there if this makes sense to others. The other more challenging piece would be to figure out whats going on in _maybe_chunk() to cause memory growth. The problem is specific to this function rather than any particular storage backend (other than the difference in default chunk args).

What you expected to happen: Memory usage should not grow when opening a zarr dataset within a Flask route.

Minimal Complete Verifiable Example:

```python from flask import Flask import xarray as xr import gc import dask.array as da

save a test dataset to zarr locally

ds_test = xr.Dataset({"foo": (["x", "y", "z"], da.random.random(size=(300,300,300)))}) ds_test.to_zarr('test.zarr', mode='w')

app = Flask(name)

ping this route repeatedly to see memory increase

@app.route('/open_zarr') def open_zarr(): # with default chunks='auto', memory grows, with chunks=None, memory is ok ds = xr.open_zarr('test.zarr', chunks='auto').compute() # Try to explicity clear memory but this doesn't help del ds gc.collect() return 'check memory'

if name == 'main': app.run(host='0.0.0.0', port=8080, debug=True) ```

Anything else we need to know?:

Environment: