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From Jeffrey Kesselman <jef...@gmail.com>
Subject Re: What does a write lock ?
Date Fri, 08 Jul 2011 02:30:23 GMT
Not confusing, but assuming a few things.

I made a more detailed post in the Datatstax forums.

On Thu, Jul 7, 2011 at 10:27 PM, Jonathan Ellis <jbellis@gmail.com> wrote:

> Sounds to me like you're confusing atomicity with isolation.
>
> On Thu, Jul 7, 2011 at 2:54 PM, Jeffrey Kesselman <jeffpk@gmail.com>
> wrote:
> > Yup, im even more confused.    Lets talk about the model, not the
> > implementation.
> > AIUI updates to a row are atomic across all columns in that row at once,
> > true?
> > If true then the next question is, does the validation happen inside or
> > outside of that guarantee, and is the row guaranteed not to change
> between
> > validation and update?
> > If that is *not* the case then it makes a whole class of solutions to
> > synchronization problems fail and puts my larger project
> > in serious question.
> >
> > On Thu, Jul 7, 2011 at 3:43 PM, Yang <teddyyyy123@gmail.com> wrote:
> >>
> >> no , the memtable is a concurrentskiplistmap
> >>
> >> insertion can happen in parallel
> >>
> >> On Jul 7, 2011 9:24 AM, "Jeffrey Kesselman" <jeffpk@gmail.com> wrote:
> >> > This has me more confused.
> >> >
> >> > Does this mean that ALL rows on a given node are only updated
> >> > sequentially,
> >> > never in parallel?
> >> >
> >> > On Thu, Jul 7, 2011 at 3:21 PM, Yang <teddyyyy123@gmail.com> wrote:
> >> >
> >> >> just to add onto what jonathan said
> >> >>
> >> >> the columns are immutable . if u overwrite/ reconcile a new obj is
> >> >> created and shoved into the memtable
> >> >>
> >> >> there is a shared lock for all writes though which guard against an
> >> >> exclusive lock on memtable switching/flushing
> >> >> On Jul 7, 2011 7:51 AM, "A J" <s5alye@gmail.com> wrote:
> >> >> > Does a write lock:
> >> >> > 1. Just the columns in question for the specific row in question
?
> >> >> > 2. The full row in question ?
> >> >> > 3. The full CF ?
> >> >> >
> >> >> > I doubt read does any locks.
> >> >> >
> >> >> > Thanks.
> >> >>
> >> >
> >> >
> >> >
> >> > --
> >> > It's always darkest just before you are eaten by a grue.
> >
> >
> >
> > --
> > It's always darkest just before you are eaten by a grue.
> >
>
>
>
> --
> Jonathan Ellis
> Project Chair, Apache Cassandra
> co-founder of DataStax, the source for professional Cassandra support
> http://www.datastax.com
>



-- 
It's always darkest just before you are eaten by a grue.

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