yes, yes, yes. A compaction on a single sstable will only get rid of tombstones if there is no live data that tombstone shadows in any other sstable.
to actually remove data with a tombstone the compaction needs to include other sstables that contain data the tombstone covers, and the tombstone will only finally be removed if all that data is removed AND GCGS has passed. Note that thugs could happen gradually over a long period of time for a specific tombstone, it doesn't need to be in a single compaction with all the other data at once, it will remove the data incrementally through multiple compactions. On 22 Sep. 2017 06:45, "Durity, Sean R" <sean_r_dur...@homedepot.com> wrote: So, let me make sure my assumptions are correct (and let others learn as well): - A major compaction would read all sstables at once (ignoring the max_threshold), thus the potential for needing double the disk space (of course if it wrote 30% less, it wouldn’t be double…) - Major compaction would leave one massive sstable, that wouldn’t get automatically compacted for a long time - A user-defined compaction on 1 sstable would not evict any tombstoned data that is in any other sstable (like a newer one with the deletes…). It would only remove data if the tombstone is already in the same sstable. Sean Durity *From:* Jeff Jirsa [mailto:jji...@gmail.com] *Sent:* Thursday, September 21, 2017 2:51 PM *To:* user@cassandra.apache.org *Subject:* Re: Massive deletes -> major compaction? The major compaction is most efficient but can temporarily double (nearly) disk usage - if you can afford that, go for it. Alternatively you can do a user-defined compaction on each sstable in reverse generational order (oldest first) and as long as the data is minimally overlapping it’ll purge tombstones that way as well - takes longer but much less disk involved. -- Jeff Jirsa On Sep 21, 2017, at 11:27 AM, Durity, Sean R <sean_r_dur...@homedepot.com> wrote: Cassandra version 2.0.17 (yes, it’s old – waiting for new hardware/new OS to upgrade) In a long-running system with billions of rows, TTL was not set. So a one-time purge is being planned to reduce disk usage. Records older than a certain date will be deleted. The table uses size-tiered compaction. Deletes are probably 25-40% of the complete data set. To actually recover the disk space, would you recommend a major compaction after the gc_grace_seconds time? I expect compaction would then need to be scheduled regularly (ick)… We also plan to re-insert the remaining data with a calculated TTL, which could also benefit from compaction. Sean Durity ------------------------------ The information in this Internet Email is confidential and may be legally privileged. It is intended solely for the addressee. Access to this Email by anyone else is unauthorized. If you are not the intended recipient, any disclosure, copying, distribution or any action taken or omitted to be taken in reliance on it, is prohibited and may be unlawful. When addressed to our clients any opinions or advice contained in this Email are subject to the terms and conditions expressed in any applicable governing The Home Depot terms of business or client engagement letter. The Home Depot disclaims all responsibility and liability for the accuracy and content of this attachment and for any damages or losses arising from any inaccuracies, errors, viruses, e.g., worms, trojan horses, etc., or other items of a destructive nature, which may be contained in this attachment and shall not be liable for direct, indirect, consequential or special damages in connection with this e-mail message or its attachment. ------------------------------ The information in this Internet Email is confidential and may be legally privileged. It is intended solely for the addressee. Access to this Email by anyone else is unauthorized. If you are not the intended recipient, any disclosure, copying, distribution or any action taken or omitted to be taken in reliance on it, is prohibited and may be unlawful. When addressed to our clients any opinions or advice contained in this Email are subject to the terms and conditions expressed in any applicable governing The Home Depot terms of business or client engagement letter. The Home Depot disclaims all responsibility and liability for the accuracy and content of this attachment and for any damages or losses arising from any inaccuracies, errors, viruses, e.g., worms, trojan horses, etc., or other items of a destructive nature, which may be contained in this attachment and shall not be liable for direct, indirect, consequential or special damages in connection with this e-mail message or its attachment.
