In my experience, the 50% overhead for compaction/upgrade is for the worst case scenario systems – where the data is primarily one table and uses size-tiered compaction. (I have one of those.) What I really look at is if there is enough space to execute upgradesstables on the largest sstable. Granted, it is not fun to deal with tight space on a Cassandra cluster.
Sean R. Durity From: Bowen Song <bo...@bso.ng> Sent: Tuesday, January 11, 2022 6:50 AM To: user@cassandra.apache.org Subject: [EXTERNAL] Re: about memory problem in write heavy system.. You don't really need 50% of free disk space available if you don't keep backups and snapshots on the same server. The DataStax guide recommends 50% free space because it recommands you to take a snapshot (which is implemented as filesystem hardlink) before upgrading. If you don't have 50% free disk space before upgrading Cassandra, you can choose to keep the backup files elsewhere, or don't make a backup at all. The later is of course not recommended for a production system. On 11/01/2022 01:36, Eunsu Kim wrote: Thank you Bowen. As can be seen from the chart, the memory of existing nodes has increased since new nodes were added. And I stopped writing a specific table. Write throughput decreased by about 15%. And memory usage began to decrease. I'm not sure if this was done by natural resolution or by reducing writing. What is certain is that the addition of new nodes has increased the native memory usage of some existing nodes. After reading the 3.x to 4.x migration guide of DataStax, it seems that more than 50% of disk availability is required for upgrade. This is likely to be a major obstacle to upgrading the cluster in operation. Many thanks. 2022. 1. 10. 오후 8:53, Bowen Song <bo...@bso.ng<mailto:bo...@bso.ng>> 작성: Anything special about the table you stopped writing to? I'm wondering how did you locate the table was the cause of the memory usage increase. > For the latest version (3.11.11) upgrade, can the two versions coexist in the > cluster for a while? > > Can the 4.x version coexist as well? Yes and yes. It is expected that two different versions of Cassandra will be running in the same cluster at the same time while upgrading. This process is often called zero downtime upgrade or rolling upgrade. You can perform such upgrade from 3.11.4 to 3.11.11 or directly to 4.0.1, both are supported. Surprisingly, I can't find any documentation related to this on the cassandra.apache.org [cassandra.apache.org]<https://urldefense.com/v3/__http:/cassandra.apache.org__;!!M-nmYVHPHQ!Z0Nt21HvLU3qhCDXc1d7WDAKhov_9nkU9VfXs6k8ZTRiJxY_qqSZWZL0_fbB9ADkpurx0Ro$> website (if you found it, please send me a link). Some other sites have brief guides on this process, such as DataStax [datastax.com]<https://urldefense.com/v3/__https:/www.datastax.com/learn/whats-new-for-cassandra-4/migrating-cassandra-4x*how-the-migration-works__;Iw!!M-nmYVHPHQ!Z0Nt21HvLU3qhCDXc1d7WDAKhov_9nkU9VfXs6k8ZTRiJxY_qqSZWZL0_fbB9ADk50dJESU$> and Instaclustr [instaclustr.com]<https://urldefense.com/v3/__https:/www.instaclustr.com/support/documentation/cassandra/cassandra-cluster-operations/cassandra-version-upgrades/__;!!M-nmYVHPHQ!Z0Nt21HvLU3qhCDXc1d7WDAKhov_9nkU9VfXs6k8ZTRiJxY_qqSZWZL0_fbB9ADkyC5PUA0$>, and you should always read the release notes [github.com]<https://urldefense.com/v3/__https:/github.com/apache/cassandra/blob/trunk/NEWS.txt__;!!M-nmYVHPHQ!Z0Nt21HvLU3qhCDXc1d7WDAKhov_9nkU9VfXs6k8ZTRiJxY_qqSZWZL0_fbB9ADki7JcB-Y$> which includes breaking changes and new features before you perform an upgrade. On 10/01/2022 00:18, Eunsu Kim wrote: Thank you for your response Fortunately, memory usage came back down over the weekend. I removed the writing of a specific table last Friday. <붙여넣은 그래픽-2.png> For the latest version (3.11.11) upgrade, can the two versions coexist in the cluster for a while? Can the 4.x version coexist as well? 2022. 1. 8. 오전 1:26, Jeff Jirsa <jji...@gmail.com<mailto:jji...@gmail.com>> 작성: 3.11.4 is a very old release, with lots of known bugs. It's possible the memory is related to that. If you bounce one of the old nodes, where does the memory end up? On Thu, Jan 6, 2022 at 3:44 PM Eunsu Kim <eunsu.bil...@gmail.com<mailto:eunsu.bil...@gmail.com>> wrote: Looking at the memory usage chart, it seems that the physical memory usage of the existing node has increased since the new node was added with auto_bootstrap=false. <붙여넣은 그래픽-1.png> On Fri, Jan 7, 2022 at 1:11 AM Eunsu Kim <eunsu.bil...@gmail.com<mailto:eunsu.bil...@gmail.com>> wrote: Hi, I have a Cassandra cluster(3.11.4) that does heavy writing work. (14k~16k write throughput per second per node) Nodes are physical machine in data center. Number of nodes are 30. Each node has three data disks mounted. A few days ago, a QueryTimeout problem occurred due to Full GC. So, referring to this blog(https://thelastpickle.com/blog/2018/04/11/gc-tuning.html [thelastpickle.com]<https://urldefense.com/v3/__https:/thelastpickle.com/blog/2018/04/11/gc-tuning.html__;!!M-nmYVHPHQ!Z0Nt21HvLU3qhCDXc1d7WDAKhov_9nkU9VfXs6k8ZTRiJxY_qqSZWZL0_fbB9ADklbhs9m0$>), it seemed to have been solved by changing the memtable_allocation_type to offheap_objects. But today, I got an alarm saying that some nodes are using more than 90% of physical memory. (115GiB /125GiB) Native memory usage of some nodes is gradually increasing. All tables use TWCS, and TTL is 2 weeks. Below is the applied jvm option. -Xms31g -Xmx31g -XX:+UseG1GC -XX:G1RSetUpdatingPauseTimePercent=5 -XX:MaxGCPauseMillis=500 -XX:InitiatingHeapOccupancyPercent=70 -XX:ParallelGCThreads=24 -XX:ConcGCThreads=24 … What additional things can I try? I am looking forward to the advice of experts. Regards. INTERNAL USE
