from http://wiki.apache.org/cassandra/ArchitectureInternals:
Making this concurrency-safe without blocking writes or reads while we remove the old SSTables from the list and add the new one is tricky, because naive approaches require waiting for all readers of the old sstables to finish before deleting them (since we can't know if they have actually started opening the file yet; if they have not and we delete the file first, they will error out). The approach we have settled on is to not actually delete old SSTables synchronously; instead we register a phantom reference with the garbage collector, so when no references to the SSTable exist it will be deleted. (We also write a compaction marker to the file system so if the server is restarted before that happens, we clean out the old SSTables at startup time.) On Tue, May 11, 2010 at 10:50 AM, Schubert Zhang <zson...@gmail.com> wrote: > In current 0.6.1, after a long time of compation, the old SSTable files are > still there, with the mark of > "CFName-id-Compacted" zero sized file. > > Whey not delete them immediately? What is the policy in 0.6.1? > > See following examples. > > -rw-rw-r-- 1 cassandra cassandra 0 May 11 23:35 LZO-1263-Compacted > -rw-rw-r-- 1 cassandra cassandra 3643422558 May 11 12:21 LZO-1263-Data.db > -rw-rw-r-- 1 cassandra cassandra 939685 May 11 12:21 LZO-1263-Filter.db > -rw-rw-r-- 1 cassandra cassandra 6034764 May 11 12:21 LZO-1263-Index.db > -rw-rw-r-- 1 cassandra cassandra 0 May 11 23:35 LZO-1597-Compacted > -rw-rw-r-- 1 cassandra cassandra 2365082186 May 11 14:49 LZO-1597-Data.db > -rw-rw-r-- 1 cassandra cassandra 751765 May 11 14:49 LZO-1597-Filter.db > -rw-rw-r-- 1 cassandra cassandra 6034764 May 11 14:49 LZO-1597-Index.db > -rw-rw-r-- 1 cassandra cassandra 0 May 11 23:35 LZO-1614-Compacted > -rw-rw-r-- 1 cassandra cassandra 31064427729 May 11 16:42 LZO-1614-Data.db > -rw-rw-r-- 1 cassandra cassandra 751765 May 11 16:42 LZO-1614-Filter.db > -rw-rw-r-- 1 cassandra cassandra 6034764 May 11 16:42 LZO-1614-Index.db > -rw-rw-r-- 1 cassandra cassandra 0 May 11 23:35 LZO-1879-Compacted > -rw-rw-r-- 1 cassandra cassandra 3536115771 May 11 17:29 LZO-1879-Data.db > -rw-rw-r-- 1 cassandra cassandra 751765 May 11 17:29 LZO-1879-Filter.db > -rw-rw-r-- 1 cassandra cassandra 6034764 May 11 17:29 LZO-1879-Index.db > -rw-rw-r-- 1 cassandra cassandra 0 May 11 23:35 LZO-2049-Compacted > -rw-rw-r-- 1 cassandra cassandra 7910248440 May 11 19:17 LZO-2049-Data.db > -rw-rw-r-- 1 cassandra cassandra 1691365 May 11 19:17 LZO-2049-Filter.db > -rw-rw-r-- 1 cassandra cassandra 6034764 May 11 19:17 LZO-2049-Index.db > -rw-rw-r-- 1 cassandra cassandra 0 May 11 23:35 LZO-2169-Compacted > -rw-rw-r-- 1 cassandra cassandra 417646680 May 11 19:56 LZO-2169-Data.db > -rw-rw-r-- 1 cassandra cassandra 2500645 May 11 19:56 LZO-2169-Filter.db > -rw-rw-r-- 1 cassandra cassandra 6034764 May 11 19:56 LZO-2169-Index.db > -rw-rw-r-- 1 cassandra cassandra 0 May 11 23:35 LZO-2184-Compacted > -rw-rw-r-- 1 cassandra cassandra 3485810361 May 11 20:08 LZO-2184-Data.db > -rw-rw-r-- 1 cassandra cassandra 751765 May 11 20:08 LZO-2184-Filter.db > -rw-rw-r-- 1 cassandra cassandra 6034764 May 11 20:08 LZO-2184-Index.db > -rw-rw-r-- 1 cassandra cassandra 0 May 11 23:35 LZO-2188-Compacted > -rw-rw-r-- 1 cassandra cassandra 663325064 May 11 20:10 LZO-2188-Data.db > -rw-rw-r-- 1 cassandra cassandra 751765 May 11 20:10 LZO-2188-Filter.db > -rw-rw-r-- 1 cassandra cassandra 6034764 May 11 20:10 LZO-2188-Index.db > -rw-rw-r-- 1 cassandra cassandra 0 May 11 23:35 LZO-2189-Compacted > -rw-rw-r-- 1 cassandra cassandra 29651624 May 11 20:09 LZO-2189-Data.db > -rw-rw-r-- 1 cassandra cassandra 114789 May 11 20:09 LZO-2189-Filter.db > -rw-rw-r-- 1 cassandra cassandra 3691960 May 11 20:09 LZO-2189-Index.db > -rw-rw-r-- 1 cassandra cassandra 52910891687 May 11 23:35 LZO-2190-Data.db > -rw-rw-r-- 1 cassandra cassandra 1618405 May 11 23:35 LZO-2190-Filter.db > -rw-rw-r-- 1 cassandra cassandra 6034764 May 11 23:35 LZO-2190-Index.db > -- Jonathan Ellis Project Chair, Apache Cassandra co-founder of Riptano, the source for professional Cassandra support http://riptano.com
