Right. Although IIRC there is another OpOrder that coordinates the migration of readers from memtables to the sstables that replace them (and the reclamation of any off-heap memory associated with the memtable)
On 13 February 2018 at 22:59, Tyagi, Preetika <preetika.ty...@intel.com> wrote: > Ah I see. That makes sense. > And it doesn't have to anything with the read requests going on in > parallel with write requests, right? > I mean we read the data from memtable depending on whatever has been > written into memtable so far and return it to the client (of course > including SSTable read and timestamp comparison etc.) > > -----Original Message----- > From: Benedict Elliott Smith [mailto:bened...@apache.org] > Sent: Tuesday, February 13, 2018 2:25 PM > To: dev@cassandra.apache.org > Subject: Re: Use of OpOrder in memtable > > If you look closely, there can be multiple memtables extant at once. > While all "new" writes are routed to the latest memtable, there may still > be writes that have begun but not yet completed. The memtable cannot be > flushed until any stragglers have completed, and some stragglers *may* > still need to be routed to their designated memtable (if they had only just > begun when the flush triggered). It helps avoid these race conditions on > either side of the equation. > > On 13 February 2018 at 22:09, Tyagi, Preetika <preetika.ty...@intel.com> > wrote: > > > Hi all, > > > > I'm trying to understand the behavior of memtable when writes/flush > > operations are going on in parallel. > > > > In my understanding, once a memtable is full it is queued for flushing > > and a new memtable is created for ongoing write operations. > > However, I was looking at the code and it looks like the OpOrder class > > is used (don't understand all details) to ensure the synchronization > > between producers (writes) and consumers (batch flushes). > > So I am a bit confused about when exactly it is needed. There will > > always be only one latest memtable for write operations and all old > > memtables are flushed so where this producer/consumer interaction on > > the same memtable is needed? > > > > Thanks, > > Preetika > > > > >
