LMDB config

[jakirkham]

There are some differences between the LMDB config used here...

shm-distributed/shm_distributed/test_runs.py

Lines 19 to 25 in 4845999

	map_size=100 * 2 ** 30,
	# sync=False,
	readahead=False,
	writemap=True,
	meminit=False,
	max_spare_txns=4,
	max_readers=16,

...compared to what is used by Zarr or Zict.

Am curious how the config here started and how the current config was determined.

[martindurant]

It was not hugely thought through, just a brief skim of the docs. Happy to be shown that switching one of the flags makes a difference; although it doesn't appear to be much different in fact between mine and zarr's. (sync probably doesn't matter since we close the connection on every access, which may be a far bigger impact on performance!)