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Harish Doddi commented on CASSANDRA-2635:
-----------------------------------------
Only caveat is that we need 2x the memory with traditional compaction for this
to work. With leveled compaction this might work better.
---Yes I am assuming going forward we will be using leveled compaction rather
than size tiered. Hence unless the user unsets this flag, the default value is
true which should work for traditional implementation.
Updated the patch
> make cache skipping optional
> ----------------------------
>
> Key: CASSANDRA-2635
> URL: https://issues.apache.org/jira/browse/CASSANDRA-2635
> Project: Cassandra
> Issue Type: Improvement
> Reporter: Peter Schuller
> Assignee: Harish Doddi
> Priority: Minor
> Attachments: CASSANDRA-2635-075.txt, CASSANDRA-2635-trunk.txt
>
>
> We've applied this patch locally in order to turn of page skipping; not
> completely but only for compaction/repair situations where it can be directly
> detrimental in the sense of causing data to become cold even though your
> entire data set fits in memory.
> It's better than completely disabling DONTNEED because the cache skipping
> does make sense and has no relevant (that I can see) detrimental effects in
> some cases, like when dumping caches.
> The patch is against 0.7.5 right now but if the change is desired I can make
> a patch for trunk. Also, the name of the configuration option is dubious
> since saying 'false' does not actually turn it off completely. I wasn't able
> to figure out a good name that conveyed the functionality in a short brief
> name however.
> A related concern as discussed in CASSANDRA-1902 is that the cache skipping
> isn't fsync:ing and so won't work reliably on writes. If the feature is to be
> retained that's something to fix in a different ticket.
> A question is also whether to retain the default to true or change it to
> false. I'm kinda leaning to false since it's detrimental in the "easy" cases
> of little data. In "big" cases with lots of data people will have to think
> and tweak anyway, so better to put the burden on that end.
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