Peter Xie created CASSANDRA-14653: ------------------------------------- Summary: The performance of "NonPeriodicTasks" pools defined in class ScheduledExecutors is low Key: CASSANDRA-14653 URL: https://issues.apache.org/jira/browse/CASSANDRA-14653 Project: Cassandra Issue Type: Improvement Components: Compaction Environment: Cassandra nodes :
3 nodes, 330G physical memory per node , and four data directory (ssd) per node. Reporter: Peter Xie We use cassandra as backend storage for Janusgraph. when we loading huge data (~2 billion vertex, ~10 billion edges), we met an problems. At first, we use STCS as compaction strategy , but met below exception. we checked the value of "max memory lock" is unlimited and "map count" is 1 million, these values should enough for loading. last , we found this problem is caused by the virtual memory are all cosumed by cassandra. So not additional virtual memory can be used by compaction task , and below exception is thrower out. {quote}ERROR [CompactionExecutor:267] 2018-08-09 02:28:40,952 JVMStabilityInspector.javv a:74 - OutOfMemory error letting the JVM handle the error: java.lang.OutOfMemoryError: Map failed {quote} So, we change compaction strategy to LCS, this change seems can resolve the virtual memory problem. But we found another problem : Many sstables which has been compacted are still retained on disk, at last these old sstable consume so many disk space, it's causing no enough disk for saving real data. we found that so many files like "mc_txn_compaction_xxx.log" are created under the data directory. After some times' investigaton, we found that this problem is caused by "NonPeriodicTasks" thread pools. this pools is always using only one thread for processing clean task and compaction. this thread pool is instanced with class DebuggableScheduledThreadPoolExecutor, and DebuggableScheduledThreadPoolExecutor is inherit from class ScheduledThreadPoolExecutor. By reading the code of class DebuggableScheduledThreadPoolExecutor, found DebuggableScheduledThreadPoolExecutor is using an unbound task queue, and core pool size is 1. Why here use the unbound queue for queuing submitted tasks? If we using unbound queue, the thread pool wouldn't increasing thread even there so many task are blocked in queue, because unbound queue never would be full. I think here should use bound queue, so when task is heavily, more threads would created for processing them. {quote}public DebuggableScheduledThreadPoolExecutor(int corePoolSize, String threadPoolName, int priority) { super(corePoolSize, new NamedThreadFactory(threadPoolName, priority)); setRejectedExecutionHandler(rejectedExecutionHandler); } public ScheduledThreadPoolExecutor(int corePoolSize, ThreadFactory threadFactory) { super(corePoolSize, Integer.MAX_VALUE, 0, NANOSECONDS, new DelayedWorkQueue(), threadFactory); } {quote} Below is the case about clean task after compaction. there nearly 3 hours delay for removing file "mc-56525". {quote} TRACE [CompactionExecutor:81] 2018-08-16 21:22:29,664 LifecycleTransaction.java:363 - Staging for obsolescence BigTableReader(path='/sdb/data/test_2/edgestore-365b0b70a05911e8806001ebe60a5ce7/mc-56525-big-Data.db') .......... TRACE [CompactionExecutor:81] 2018-08-16 21:22:41,162 Tracker.java:165 - removing /sdb/data/test_2/edgestore-365b0b70a05911e8806001ebe60a5ce7/mc-56525-big from list of files tracked for test_2.edgestore ............ TRACE [NonPeriodicTasks:1] 2018-08-17 00:28:47,179 SSTableReader.java:2175 - Async instance tidier for /sdb/data/test_2/edgestore-365b0b70a05911e8806001ebe60a5ce7/mc-56525-big, before barrier TRACE [NonPeriodicTasks:1] 2018-08-17 00:28:47,180 SSTableReader.java:2181 - Async instance tidier for /sdb/data/test_2/edgestore-365b0b70a05911e8806001ebe60a5ce7/mc-56525-big, after barrier TRACE [NonPeriodicTasks:1] 2018-08-17 00:28:47,182 SSTableReader.java:2196 - Async instance tidier for /sdb/data/test_2/edgestore-365b0b70a05911e8806001ebe60a5ce7/mc-56525-big, completed {quote} -- This message was sent by Atlassian JIRA (v7.6.3#76005) --------------------------------------------------------------------- To unsubscribe, e-mail: commits-unsubscr...@cassandra.apache.org For additional commands, e-mail: commits-h...@cassandra.apache.org