It seems I have created some confusion.
This version of UCS (let's call it V2) is ahead of the one in DSE (V1),
with the main difference that it no longer uses a fixed number of shards.
Because of this, V2 acts similar to LCS in the required extra space,
because the sstables it constructs aim to
I’m without laptop this week but looks like
CompactionTask#reduceScopeForLimitedSpace
So maybe it just comes for free with UCS
> On Mar 17, 2023, at 6:21 PM, Jeremy Hanna wrote:
>
> You're right that it doesn't handle it in the sense that it doesn't resolve
> it the problem, but it also
You're right that it doesn't handle it in the sense that it doesn't resolve it
the problem, but it also doesn't do what STCS does. From what I've seen, STCS
blindly tries to compact and then the disk will fill up triggering the disk
failure policy. With UCS it's much less likely and if it
> On Mar 17, 2023, at 1:46 PM, Jeremy Hanna wrote:
>
>
>
> One much more graceful element of UCS is that instead of what was previously
> done with compaction strategies where the server just shuts down when running
> out of space - forcing system administrators to be paranoid about
I think it's important to highlight a few of practical elements of this work
that may not be completely clear.
Sharding ranges allows for parallel compactions - taking advantage of
additional CPUs on the server. This allows compactions to keep up much easier.
One much more graceful element of
Could we get a JIRA for this too so we can get some reviewers collaborating on
this? Only see Lorina's ticket for documenting it in JIRA atm.
On Fri, Mar 17, 2023, at 9:53 AM, Branimir Lambov wrote:
> The prototype of UCS can now be found in this pull request:
>
The prototype of UCS can now be found in this pull request:
https://github.com/apache/cassandra/pull/2228
Its description is given in the included markdown documentation:
https://github.com/blambov/cassandra/blob/UCS-density/src/java/org/apache/cassandra/db/compaction/UnifiedCompactionStrategy.md
I’m personally very excited by this work. Compaction could do with a spring clean and this feels to formalise things much more cleanly, but density tiering in particular is something I’ve wanted to incorporate for years now, as it should significantly improve STCS behaviour (most importantly
I noticed the CEP doesn't link to this, so it should be worth mentioning
that the UCS documentation is available here:
https://github.com/datastax/cassandra/blob/ds-trunk/doc/unified_compaction.md
Both of the above seem to do a poor job referencing the literature we've
been inspired by. I will
Hello everyone,
I would like to open the discussion on our proposal for a unified
compaction strategy that aims to solve well-known problems with compaction
and improve parallelism to permit higher levels of sustained write
throughput.
The proposal is here:
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