The org.apache.activemq.store.kahadb.MessageDatabase <https://github.com/apache/activemq/blob/master/activemq-kahadb-store/src/main/java/org/apache/activemq/store/kahadb/MessageDatabase.java>.CheckpointRunner does the following:
1. If the journal does periodic disk syncing rather than immediate syncing and the sync period has elapsed, it causes unsynced content to be written to disk. 2. If the cleanup interval has elapsed, it performs cleanup (identifies and deletes files that contain no unacknowledged messages, performs ack compaction if enabled, flushes any pending index-modifying operations in the pagefile, and then deletes any files that are no longer referenced). 3. If the checkpoint interval has elapsed, it performs a checkpoint (flushes any pending index-modifying operations in the pagefile, and then deletes any files that are no longer referenced) - basically a cleanup without the search for files that can be GC'ed and the ack compaction. The consequences of increasing the period of these events are the following: 1. If you're doing periodic disk syncing, you incur a greater risk of losing data. If not, there is no effect on this particular dimension. 2. Because the pagefile stays the same but you're going longer before flushing, you're more likely to fill it before the next flush, in which case writes are done either in the background or synchronously within the current thread, which may be less efficient. So your throughput could drop, but how much would probably depend heavily on how heavily you're using the persistent store. You asked whether there was any negative impact of having it run less frequently, but I'll turn the question around: what positive impact do you believe you'll achieve by having it run less frequently, such that it's worth 1) your time, and 2) the increased odds of hitting edge cases caused by running in an uncommonly-used configuration? Have you measured a performance impact of the operations of that thread? Tim P.S. All information in this email comes from some time this evening reading through this code for the first time, so it's entirely possible that I've missed or misrepresented something here. YMMV. On Fri, Oct 20, 2017 at 1:44 PM, Raffi <raffi.onj...@gmail.com> wrote: > It's my understanding each kahadb is assigned a checkpoint thread which, > every 5s (default), wakes up and does something; what is it doing, and is > there any negative impact if the interval is increased to 60s or 120s? We > are using persistent messages, jsyk > > > > -- > Sent from: http://activemq.2283324.n4.nabble.com/ActiveMQ-User- > f2341805.html >
