Please do.
On Fri, Dec 4, 2009 at 5:53 PM, Ramzi Rabah <[email protected]> wrote: > Thanks Jonathan. > Should I open a bug for this? > > Ray > > On Fri, Dec 4, 2009 at 3:47 PM, Jonathan Ellis <[email protected]> wrote: >> On Fri, Dec 4, 2009 at 5:32 PM, Ramzi Rabah <[email protected]> wrote: >>> Starting with fresh directories with no data and trying to do simple >>> inserts, I could not reproduce it *sigh*. Nothing is simple :(, so I >>> decided to dig deeper into the code. >>> >>> I was looking at the code for compaction, and this is a very noob >>> concern, so please bare with me if I'm way off, this code is all new >>> to me. When we are doing compactions during the normal course of >>> cassandra, we call: >>> >>> for (List<SSTableReader> sstables : >>> getCompactionBuckets(ssTables_, 50L * 1024L * 1024L)) >>> { >>> if (sstables.size() < minThreshold) >>> { >>> continue; >>> } >>> other wise docompactions... >>> >>> where getCompactionBuckets puts in buckets very small files, or files >>> that are 0.5-1.5 of each other's sizes. It will only compact those if >>> they are >= minimum threshold which is 4 by default. >> >> Exactly right. >> >>> So far so good. Now how about this scenario, I have an old entry that >>> I inserted long time ago and that was compacted into a 75MB file. >>> There are fewer 75MB files than 4. I do many deletes, and I end with 4 >>> extra sstable files filled with tombstones, each about 300 MB large. >>> These 4 files are compacted together and in the compaction code, if >>> the tombstone is there we don't copy it over to the new file. Now >>> since we did not compact the 75MB files, but we compacted the >>> tombstone files, doesn't that leave us with the tombstone gone, but >>> the data still intact in the 75MB file? >> >> Also right. Glad you had a look! :) >> >> One relatively easy fix would be to only GC the tombstones if there >> are no SSTables left for that CF older than the ones being compacted. >> (So, a "major" compaction, which compacts all SSTables and is what >> nodeprobe invokes, would always GC eligible tombstones.) >> >> -Jonathan >> >
