+100 to this We'd have to come up w/ a pretty compelling counterexample to NOT switch the default to mmap_index_only at this point.
On Wed, Sep 6, 2023 at 11:40 AM Brandon Williams <dri...@gmail.com> wrote: > Given https://issues.apache.org/jira/browse/CASSANDRA-17237 I think it > makes sense. At the least I think we should restore disk_access_mode > so that users are more aware of the options available. > > Kind Regards, > Brandon > > On Wed, Sep 6, 2023 at 10:50 AM Paulo Motta <pauloricard...@gmail.com> > wrote: > > > > Hi, > > > > I've been bitten by OOMs with disk_access_mode:auto/mmap that were fixed > by changing to disk_access_mode:mmap_index_only. In a particular benchmark > I got 5x more read throughput on 3.11.x with disk_access_mode: > mmap_index_only vs disk_access_mode: auto/mmap. > > > > Changing disk_access_mode to mmap_index_only seems to be a common > recommendation on forums[1][2][3][4] and slack (find by searching > disk_access_mode in the #cassandra channel on https://the-asf.slack.com/). > > > > It's not clear to me when using the default disk_access_mode:auto/mmap > is beneficial, perhaps only when the read set fits in memory? Mick seems to > think on CASSANDRA-15531 [5], that mmap_index_only has a higher heap cost > and should be only used when warranted. However it's not uncommon to see > people being bitten with OOMs or lower read performance due to the default > disk_access_mode, so it makes me think it's not the best fool-proof default. > > > > Should we consider changing default "auto" behavior of > "disk_access_mode" to be "mmap_index_only" instead of "mmap" in 5.0 since > it's likely safer and perhaps more performant? > > > > Thanks, > > > > Paulo > > > > [1] > https://stackoverflow.com/questions/72272035/troubleshooting-and-fixing-cassandra-oom-issue > > [2] https://phabricator.wikimedia.org/T137419 > > [3] https://stackoverflow.com/a/55975471 > > [4] > https://support.datastax.com/s/article/FAQ-Use-of-disk-access-mode-in-DSE-51-and-earlier > > [5] https://issues.apache.org/jira/browse/CASSANDRA-15531 >
