Links order

[axelboc]

Hi @jreadey! With the REST API, is there a way to request the links in a group in the same order as they were created?

Here's what I'm doing:

1. Create an HDF5 file with h5py and h5py.get_config().track_order = True
2. Add datasets to the root of the file
3. Load the file into HSDS with hsload
4. GET the links of the root group — e.g. http://localhost:5101/groups/g-db06b970-804343aa-538e-31f808-cbcb22/links?domain=/sample-hsds.h5

Problem: the links are ordered alphabetically in the JSON response.

[jreadey]

Hey @axelboc, sorry for the delayed response, I missed this issue.

That behavior is expected -- currently hsload doesn't query the group creation properties.
Actually, I'm not sure how to query these. If I do:

f.id.get_create_plist().get_link_creation_order()

I always getting 0 regardless if track order is set at file creation time.
What result do you get with your file?

[axelboc]

No worries!

Looking at the group.keys() iterator code in h5py: https://github.com/h5py/h5py/blob/09e0ca654796473e469826ebb056b2abeec156b9/h5py/h5g.pyx#L119, I think it's because the creation order flag has to be retrieved from the root group object, not from the file object:

f["/"].id.get_create_plist().get_link_creation_order() # 3 (`CRT_ORDER_TRACKED | CRT_ORDER_INDEXED`)

[jreadey]

I spent some time working on this, but it's a bit more challenging then I expected. Getting the create_order flag is easy enough, and I can initialize the HSDS objects property list, but when calling visit on the source file, the objects are visited based on the alphanumeric ordering of the links, not the creation order. And that in turn causes the creation time to not be consisted with the source files creation time.

If this is not urgent, I'd like to come back to this issue as part of the HSDS 1.0 release (and corresponding h5pyd release). I think it should be easier to deal with based on some updates I've already made in the release branch.

The 1.0 release should be out in 4-6 weeks.

[axelboc]

Sounds great, no rush on my end. Thanks a lot for looking at it!