If you drop window size, you may force some window-major compactions (if you go from 1 week windows to 1 day windows, you’ll have 6 days worth of files start compacting into 1-day sstables).
If you increase window size, you’ll likely have adjacent windows join (if you go from 1 day windows to 2 day windows, nearly every sstable will be joined with the one in the day adjacent to it). Short of altering compaction strategies, it seems unlikely that you’d see huge jumps where you’d run out of space. How many tables/CFs have TWCS enabled? How much space are you using, and how much is free? Do you have hundreds with the same TWCS parameters? If you’re running very close to your capacity, you may want to consider dropping concurrent compactors down so fewer compaction tasks run at the same time. That will translate proportionally to the amount of extra disk you have consumed by compaction in a TWCS setting. From: Seth Edwards <s...@pubnub.com> Reply-To: "user@cassandra.apache.org" <user@cassandra.apache.org> Date: Sunday, October 23, 2016 at 7:03 PM To: user <user@cassandra.apache.org> Subject: Re: Question about compaction strategy changes More compactions meaning "rows to be compacted" or actual number of pending compactions? I assumed when I run nodetool compactionstats the number of pending tasks would line up with number of sstables that will be compacted. Most of the time this is idle, then we hit spots when it could jump into the thousands and we and up being short of a few hundred GB of disk space. On Sun, Oct 23, 2016 at 5:49 PM, kurt Greaves <k...@instaclustr.com> wrote: On 22 October 2016 at 03:37, Seth Edwards <s...@pubnub.com> wrote: We're using TWCS and we notice that if we make changes to the options to the window unit or size, it seems to implicitly start recompacting all sstables. If you increase the window unit or size you potentially increase the number of SSTable candidates for compaction inside each window, which is why you would see more compactions. If you decrease the window you shouldn't see any new compactions kicked off, however be aware that you will have SSTables covering multiple windows, so until a full cycle of your TTL passes your read queries won't benefit from the smaller window size. Kurt Greaves k...@instaclustr.com www.instaclustr.com CONFIDENTIALITY NOTE: This e-mail and any attachments are confidential and may be legally privileged. If you are not the intended recipient, do not disclose, copy, distribute, or use this email or any attachments. If you have received this in error please let the sender know and then delete the email and all attachments.
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