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>

> 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
> >
> >

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