[r] Out-of-memory issues on cellxgene_census R acceptance tests

[johnkerl]

This may, of course, be a bug within cellxgene_census. However, the Python and R APIs should be working similarly enough that if one API is not OOMing and another is OOMing, on the same dataset and query pattern, there is likely either a TileDB-SOMA code flaw or a TileDB-SOMA documentation flaw.

Reported by @ebezzi.

[johnkerl]

@ebezzi were these resolved by adding rm and gc calls to your R test cases?

[ebezzi]

Yeah, that specific test was fixed via rm+gc. There is still a test that sometimes fails because of OOM (test_seurat_common-cell-type-large-buffer-size), and it's not a garbage collection issue since this test loads everything in memory. We'll monitor and see how frequent the failures are, and worst case we'll lower the limit of queried cells (right now it's 15M).