[ https://issues.apache.org/jira/browse/CASSANDRA-8414?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14233485#comment-14233485 ]
Benedict commented on CASSANDRA-8414: ------------------------------------- I've edited the title because it's not quite that compaction is O(n^2), but that certain operations within a partition are. It's also not limited to just that specific method. The best solution is probably to introduce a special deletion iterator on which a call to remove() simply sets a corresponding bit to 1; once we exhaust the iterator we commit the deletes in one pass. > Avoid loops over array backed iterators that call iter.remove() > --------------------------------------------------------------- > > Key: CASSANDRA-8414 > URL: https://issues.apache.org/jira/browse/CASSANDRA-8414 > Project: Cassandra > Issue Type: Bug > Components: Core > Reporter: Richard Low > > I noticed from sampling that sometimes compaction spends almost all of its > time in iter.remove() in ColumnFamilyStore.removeDeletedStandard. It turns > out that the cf object is using ArrayBackedSortedColumns, so deletes are from > an ArrayList. If the majority of your columns are GCable tombstones then this > is O(n^2). The data structure should be changed or a copy made to avoid this. -- This message was sent by Atlassian JIRA (v6.3.4#6332)