cassandra-user mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From Carlos Alonso <i...@mrcalonso.com>
Subject Re: Inconsistent Reads after Restoring Snapshot
Date Fri, 29 Apr 2016 08:12:44 GMT
If I understand correctly, your reads will always return the value from B
as that cell will have the highest timestamp.

Consistent reads (CL >= QUORUM) will request data from all replica nodes
and compare the results in the coordinator, returning the value if they all
agree or returning the one with highest timestamp (last write wins) if they
don't agree, and running a read repair (repair that particular record) if
the nodes didn't agreed.

Hope this helps.

Carlos Alonso | Software Engineer | @calonso <https://twitter.com/calonso>

On 29 April 2016 at 04:33, Anuj Wadehra <anujw_2003@yahoo.co.in> wrote:

> Sean,
>
> I meant commit log archival was never part of "restoring snapshot"
> DataStax documentation. How commitlog archival is related to my concern?
> Please elaborate.
>
> Thanks
> Anuj
>
> Sent from Yahoo Mail on Android
> <https://overview.mail.yahoo.com/mobile/?.src=Android>
>
> On Thu, 28 Apr, 2016 at 9:24 PM, SEAN_R_DURITY@homedepot.com
> <SEAN_R_DURITY@homedepot.com> wrote:
>
>
> https://docs.datastax.com/en/cassandra/2.0/cassandra/configuration/configLogArchive_t.html
>
>
>
> Sean Durity
>
>
>
> *From:* Anuj Wadehra [mailto:anujw_2003@yahoo.co.in]
> *Sent:* Wednesday, April 27, 2016 10:44 PM
> *To:* user@cassandra.apache.org
> *Subject:* RE: Inconsistent Reads after Restoring Snapshot
>
>
>
> No.We are not saving them.I have never read that in DataStax documentation.
>
>
>
> Thanks
>
> Anuj
>
> Sent from Yahoo Mail on Android
> <https://overview.mail.yahoo.com/mobile/?.src=Android>
>
>
>
> On Thu, 28 Apr, 2016 at 12:45 AM, SEAN_R_DURITY@homedepot.com
>
> <SEAN_R_DURITY@homedepot.com> wrote:
>
> What about the commitlogs? Are you saving those off anywhere in between
> the snapshot and the crash?
>
>
>
>
>
> Sean Durity
>
>
>
> *From:* Anuj Wadehra [mailto:anujw_2003@yahoo.co.in]
> *Sent:* Monday, April 25, 2016 10:26 PM
> *To:* User
> *Subject:* Inconsistent Reads after Restoring Snapshot
>
>
>
> Hi,
>
>
>
> We have 2.0.14. We use RF=3 and read/write at Quorum. Moreover, we dont
> use incremental backups. As per the documentation at
> https://docs.datastax.com/en/cassandra/2.0/cassandra/operations/ops_backup_snapshot_restore_t.html
,
> if i need to restore a Snapshot on SINGLE node in a cluster, I would run
> repair at the end. But while the repair is going on, reads may get
> inconsistent.
>
>
>
>
>
> Consider following scenario:
>
> 10 AM Daily Snapshot taken of node A and moved to backup location
>
> 11 AM A record is inserted such that node A and B insert the record but
> there is a mutation drop on node C.
>
> 1 PM Node A crashes and data is restored from latest 10 AM snapshot. Now,
> only Node B has the record.
>
>
>
> Now, my question is:
>
>
>
> Till the repair is completed on node A,a read at Quorum may return
> inconsistent result based on the nodes from which data is read.If data is
> read from node A and node C, nothing is returned and if data is read from
> node A and node B, record is returned. This is a vital point which is not
> highlighted anywhere.
>
>
>
>
>
> Please confirm my understanding.If my understanding is right, how to make
> sure that my reads are not inconsistent while a node is being repair after
> restoring a snapshot.
>
>
>
> I think, autobootstrapping the node without joining the ring till the
> repair is completed, is an alternative option. But snapshots save lot of
> streaming as compared to bootstrap.
>
>
>
> Will incremental backups guarantee that
>
>
>
> Thanks
>
> Anuj
>
>
>
>
>
> Sent from Yahoo Mail on Android
> <https://overview.mail.yahoo.com/mobile/?.src=Android>
>
>
> ------------------------------
>
>
> The information in this Internet Email is confidential and may be legally
> privileged. It is intended solely for the addressee. Access to this Email
> by anyone else is unauthorized. If you are not the intended recipient, any
> disclosure, copying, distribution or any action taken or omitted to be
> taken in reliance on it, is prohibited and may be unlawful. When addressed
> to our clients any opinions or advice contained in this Email are subject
> to the terms and conditions expressed in any applicable governing The Home
> Depot terms of business or client engagement letter. The Home Depot
> disclaims all responsibility and liability for the accuracy and content of
> this attachment and for any damages or losses arising from any
> inaccuracies, errors, viruses, e.g., worms, trojan horses, etc., or other
> items of a destructive nature, which may be contained in this attachment
> and shall not be liable for direct, indirect, consequential or special
> damages in connection with this e-mail message or its attachment.
>
>
>
>
> ------------------------------
>
> The information in this Internet Email is confidential and may be legally
> privileged. It is intended solely for the addressee. Access to this Email
> by anyone else is unauthorized. If you are not the intended recipient, any
> disclosure, copying, distribution or any action taken or omitted to be
> taken in reliance on it, is prohibited and may be unlawful. When addressed
> to our clients any opinions or advice contained in this Email are subject
> to the terms and conditions expressed in any applicable governing The Home
> Depot terms of business or client engagement letter. The Home Depot
> disclaims all responsibility and liability for the accuracy and content of
> this attachment and for any damages or losses arising from any
> inaccuracies, errors, viruses, e.g., worms, trojan horses, etc., or other
> items of a destructive nature, which may be contained in this attachment
> and shall not be liable for direct, indirect, consequential or special
> damages in connection with this e-mail message or its attachment.
>
>

Mime
View raw message