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The "FAQ_JP" page has been changed by MakiWatanabe. The comment on this change is: Add latest faq "jna". http://wiki.apache.org/cassandra/FAQ_JP?action=diff&rev1=71&rev2=72 -------------------------------------------------- * [[#unsubscribe|メーリングリストの配信を停止するにはどうしたらいいですか？]] * [[#cleaning_compacted_tables|Compactionを実行してもディスク使用量が減らないのはなぜでしょうか？]] * [[#mmap|topコマンドの出力で，CassandraがJava heapの最大値よりも大きなメモリを使用しているのはなぜでしょうか？]] + * [[#jna|I'm getting java.io.IOException: Cannot run program "ln" when trying to snapshot or update a keyspace]] - - <<Anchor(cant_listen_on_ip_any)>> == CassandraはListenAddress設定で何故0.0.0.0(全アドレス)でリッスンできないのですか? == @@ -449, +448 @@ The difference between normal I/O and mmap() is that in the mmap() case the memory is actually mapped to the process, thus affecting the virtual size as reported by top. The main argument for using mmap() instead of standard I/O is the fact that reading entails just touching memory - in the case of the memory being resident, you just read it - you don't even take a page fault (so no overhead in entering the kernel and doing a semi-context switch). This is covered in more detail [[http://www.varnish-cache.org/trac/wiki/ArchitectNotes|here]]. + <<Anchor(jna)>> + + == I'm getting java.io.IOException: Cannot run program "ln" when trying to snapshot or update a keyspace == + Updating a keyspace first takes a snapshot. This involves creating hardlinks to the existing SSTables, but Java has no native way to create hard links, so it must fork "ln". When forking, there must be as much memory free as the parent process, even though the child isn't going to use it all. Because Java is a large process, this is problematic. The solution is to install [[http://jna.java.net/|Java Native Access]] so it can create the hard links itself. +
