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From Jeffrey Kesselman <jef...@gmail.com>
Subject Re: What does a write lock ?
Date Fri, 08 Jul 2011 03:41:04 GMT
Really, as i lay in the bath thinking nabout it, I concluded what I am
looking for is a very limited form of Consistency.

Its consistency over a single row on a single node just for the period of
update.

On Thu, Jul 7, 2011 at 10:34 PM, Jeffrey Kesselman <jeffpk@gmail.com> wrote:

> Its not really isolation, btw, because we arent talking about anyone seeing
> an update mid-update.    Rather, we are talking about when updates are
> allowed to occur.
>
> Atomicity means that all the updates happen together or they don't happen
> at all.
> Isolation means that no results of the update are visible until the entire
> update operation is complete.
>
> This really lies somewhere in the middle of the two concepts.   Its part of
> the results of the combined effects of ACID
>
>
> 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.
>



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

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