Howard Chu wrote:
Alec Matusis wrote:
Try repeating the test with MDB_NORDAHEAD set on the environment.
Thank you: with MDB_NORDAHEAD it works on both machines as expected. We have a couple of questions and observations.
We have: machine 1: XFS filesystem, 148GB RAM, 3.13 # blockdev --getra /dev/fiob 256 Shared memory grows to 13GB with or without MDB_NORDAHEAD (as expected)
machine 2: EXT4 filesystem, 105GB RAM, 4.15 # blockdev --getra /dev/vda2 256 Shared memory grows to 83GB without MDB_NORDAHEAD (unexpected) and to 13GB with MDB_NORDAHEAD (as expected)
Questions and observations:
- Since “blockdev --getra” shows the same 256 for both machines, why
MDB_NORDAHEAD was necessary only on machine2?
This is a stupid question. You claimed both machines have similar setups and yet they are running wildly different kernel versions and using completely different filesystems, and now you wonder why they behave differently??
None of this has anything to do with LMDB. Ask a filesystem or kernel developer.
For anyone just tuning in - we demonstrated from day 1 the huge difference in performance between different filesystems.
http://www.lmdb.tech/bench/microbench/july/#sec11