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Subject: Re: Truncate introspection
From: aaron morton <aaron@thelastpickle.com>
In-Reply-To: <BANLkTimx-7u0gj7j_hkMT6ems6sYxQffPg@mail.gmail.com>
Date: Tue, 28 Jun 2011 23:35:01 +1200
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To: user@cassandra.apache.org

Drop CF takes a snapshot of the CF first, and then marks SSTables on =
disk as compacted so they will be safely deleted later. Finally it =
removes the CF from the meta data.=20

If you see the SSTables on disk, you should see 0 length .compacted =
files for every one of them.=20

Cheers

-----------------
Aaron Morton
Freelance Cassandra Developer
@aaronmorton
http://www.thelastpickle.com

On 28 Jun 2011, at 20:00, David Boxenhorn wrote:

> Does drop work in a similar way?
>=20
> When I drop a CF and add it back with a different schema, it seems to =
work.
>=20
> But I notice that in between the drop and adding it back, when the CLI
> tells me the CF doesn't exist, the old data is still there.
>=20
> I've been assuming that this works, but just wanted to make sure...
>=20
> On Tue, Jun 28, 2011 at 12:56 AM, Jonathan Ellis <jbellis@gmail.com> =
wrote:
>> Each node (independently) has logic that guarantees that any writes
>> processed before the truncate, will be wiped out.
>>=20
>> This does not mean that each node will wipe out the same data, or =
even
>> that each node will process the truncate (which would result in a
>> timedoutexception).
>>=20
>> It also does not mean you can't have writes immediately after the
>> truncate that would race w/ a "truncate, check for zero sstables"
>> procedure.
>>=20
>> On Mon, Jun 27, 2011 at 3:35 PM, Ethan Rowe <ethan@the-rowes.com> =
wrote:
>>> If those went to zero, it would certainly tell me something =
happened.  :)  I
>>> guess watching that would be a way of seeing something was going on.
>>> Is the truncate itself propagating a ring-wide marker or anything so =
the CF
>>> is logically "empty" before being physically removed?  That's the =
impression
>>> I got from the docs but it wasn't totally clear to me.
>>>=20
>>> On Mon, Jun 27, 2011 at 3:33 PM, Jonathan Ellis <jbellis@gmail.com> =
wrote:
>>>>=20
>>>> There's a JMX method to get the number of sstables in a CF, is that
>>>> what you're looking for?
>>>>=20
>>>> On Mon, Jun 27, 2011 at 1:04 PM, Ethan Rowe <ethan@the-rowes.com> =
wrote:
>>>>> Is there any straightforward means of seeing what's going on after
>>>>> issuing a
>>>>> truncate (on 0.7.5)?  I'm not seeing evidence that anything =
actually
>>>>> happened.  I've disabled read repair on the column family in =
question
>>>>> and
>>>>> don't have anything actively reading/writing at present, apart =
from my
>>>>> one-off tests to see if rows have disappeared.
>>>>> Thanks in advance.
>>>>=20
>>>>=20
>>>>=20
>>>> --
>>>> Jonathan Ellis
>>>> Project Chair, Apache Cassandra
>>>> co-founder of DataStax, the source for professional Cassandra =
support
>>>> http://www.datastax.com
>>>=20
>>>=20
>>=20
>>=20
>>=20
>> --
>> Jonathan Ellis
>> Project Chair, Apache Cassandra
>> co-founder of DataStax, the source for professional Cassandra support
>> http://www.datastax.com
>>=20