If you have two replicas A and B, and you write at ONE A acknowledged the write, B is running but drops write, the write succeeds
A fails 30 seconds later. The data is lost because it had no chance to be repaired to the other host via hints / repair / readrepair 10 days is a big window - repair is a smaller problem than RF=2 and writing at ONE -- Jeff Jirsa > On Jun 9, 2018, at 10:52 PM, onmstester onmstester <onmstes...@zoho.com> > wrote: > > Thanks Jeff, > If i run repair every 10 days, then, would there be a chance of losing data > by losing one node (data inserted exactly after last repair) ? > > Sent using Zoho Mail > > > > ---- On Sun, 10 Jun 2018 10:14:46 +0430 Jeff Jirsa <jji...@gmail.com> wrote > ---- > > > > > On Jun 9, 2018, at 10:28 PM, onmstester onmstester <onmstes...@zoho.com> > wrote: > > I'm using RF=2 (i know it should be at least 3 but i'm short of resources) > and WCl=ONE and RCL=ONE in a cluster of 10 nodes in a insert-only scenario. > The problem: i dont want to use nodetool repair because it would put hige > load on my cluster for a long time, but also i need data consistency > and fault tolerance in a way that: > if one of my nodes fails: > 1. there would be no single record data loss > > This requires write > 1 > > 2. write/read of data would be continued with no problem > > > This requires more replicas in the ring than the number of replicas requires > for reads and writes > > > I know that current config won't satisfy No.1, so changed the Write > Consistensy Level to ALL and to satisfy No.2, i'm catching exceptions of > "1 replicas needed but 2 required", write those records again with WCL = ONE > and put them somewhere for rewrite later with WCL=2. > Is there anything wrong with this workaround? any better solution (Strong > requirements: I can't change the RF, The system should tolerate 1 node > failure with no data loss and no read/write failure) > > > Sorta works, but it’s dirty and a lot of edge cases. Depending on the budget > and value of data, maybe it’s ok, but I wouldn’t trust it to be good enough > for critical use cases > > The transient replication work that Ariel is doing > (https://issues.apache.org/jira/browse/CASSANDRA-14404) will likely benefit > you here in 4.0 (but it will require you to run repair). > >
