You are viewing a plain text version of this content. The canonical link for it is here.
Posted to user@cassandra.apache.org by Anuj Wadehra <an...@yahoo.co.in> on 2015/06/23 19:57:55 UTC
Read Consistency
Hi,
Need to validate my understanding..
RF=3 , Read CL = Quorum
What would be returned to the client in following scenarios:
Scenario 1: Read query is fired for a key, data is found on one node and not found on other two nodes who are responsible for the token corresponding to key.
Options: no data is returned OR data from the only node having data is returned?
Scenario 2: Read query is fired and all 3 replicas have different data with different timestamps.
Options: data with latest timestamp is returned OR something else???
Thanks
Anuj
Sent from Yahoo Mail on Android
Re: Read Consistency
Posted by Robert Coli <rc...@eventbrite.com>.
On Tue, Jun 30, 2015 at 11:16 AM, Tyler Hobbs <ty...@datastax.com> wrote:
>
> Correct, if you get a WriteTimeout error, you don't know if any replicas
> have written the data or not. It's even possible that all replicas wrote
> the data but didn't respond to the coordinator in time. I suspect most
> users handle this situation by retrying the write with the same timestamp
> (which makes the operation idempotent*).
>
*Unless the operation is a counter increment/decrement, in which case it
cannot be idempotent.
This is why people who need very-accurate counters should probably not use
Cassandra for them. :)
=Rob
Re: Read Consistency
Posted by Tyler Hobbs <ty...@datastax.com>.
On Tue, Jun 30, 2015 at 12:27 PM, Anuj Wadehra <an...@yahoo.co.in>
wrote:
> Agree Tyler. I think its our application problem. If client returns failed
> write in spite of retries, application must have a rollback mechanism to
> make sure old state is restored. Failed write may be because of the fact
> that CL was not met even though one node successfully wrote.Cassandra wont
> do cleanup or rollback on one node so you need to do it yourself to make
> sure that integrity of data is maintained in case strong consistency is a
> requirement. Right?
Correct, if you get a WriteTimeout error, you don't know if any replicas
have written the data or not. It's even possible that all replicas wrote
the data but didn't respond to the coordinator in time. I suspect most
users handle this situation by retrying the write with the same timestamp
(which makes the operation idempotent).
It's worth noting that if you get an Unavailable response, you are
guaranteed that the data has not been written to any replicas, because the
coordinator already knew that the replicas were down when it got the
response.
--
Tyler Hobbs
DataStax <http://datastax.com/>
Re: Read Consistency
Posted by Anuj Wadehra <an...@yahoo.co.in>.
Agree Tyler. I think its our application problem. If client returns failed write in spite of retries, application must have a rollback mechanism to make sure old state is restored. Failed write may be because of the fact that CL was not met even though one node successfully wrote.Cassandra wont do cleanup or rollback on one node so you need to do it yourself to make sure that integrity of data is maintained in case strong consistency is a requirement. Right?
We use Hector by the way and plannning to switch to CQL driver..
Thanks
Anuj Wadehra
Sent from Yahoo Mail on Android
From:"Tyler Hobbs" <ty...@datastax.com>
Date:Tue, 30 Jun, 2015 at 10:42 pm
Subject:Re: Read Consistency
I think these scenarios are still possible even when we are writing at QUORUM ..if we have dropped mutations in our cluster..
It was very strange in our case ...We had RF=3 and READ/WRITE CL=QUORUM..we had dropped mutations for long time but we never faced any scenario like scenario 1 when READ went to node 2 and 3 and read did's return any data..Any comments on this are welcome??
They are not possible if you write at QUORUM, because QUORUM guarantees that at least two of the nodes will have the most recent version of the data. If fewer than two replicas respond successfully (meaning two replicas dropped mutations), you will get an error on the write.
All of the drivers and cqlsh default to consistency level ONE, so I would double check that your application is setting the consistency level correctly.
On Sun, Jun 28, 2015 at 12:55 PM, Anuj Wadehra <an...@yahoo.co.in> wrote:
Sorry for typo in your name Owen !!
Anuj
Sent from Yahoo Mail on Android
From:"Anuj Wadehra" <an...@yahoo.co.in>
Date:Sun, 28 Jun, 2015 at 11:11 pm
Subject:Re: Read Consistency
Agree Owem !! Response in both scenarios would depend on the 2 replicas chosen for meeting QUORUM. But, the intent is to get the tricky part of scenario 1 answered i.e. when 2 nodes selected are one with and one without data.
As per my understanding of Read Path and documentation https://wiki.apache.org/cassandra/ArchitectureInternals:
1. Data would be read from closest node and digest would be received from one more replica.
2. If mismatch is found between digest, blocked read happens on same 2 replicas (not all replicas ..so in scenario 2, if 2 nodes didnt have latest data and third node has it ..still stale data would be returned)
I think these scenarios are still possible even when we are writing at QUORUM ..if we have dropped mutations in our cluster..
It was very strange in our case ...We had RF=3 and READ/WRITE CL=QUORUM..we had dropped mutations for long time but we never faced any scenario like scenario 1 when READ went to node 2 and 3 and read did's return any data..Any comments on this are welcome??
Thanks for clarifying further as discussion could have mislead few..
Thanks
Anuj
On Sunday, 28 June 2015 6:16 AM, Owen Kim <oh...@gmail.com> wrote:
Sorry. I have to jump in and disagree. Data is not guaranteed to retire in scenario 1. Since two nodes do not have data and two nodes may be the only nodes queried at that CL, the read query may return data or not.
Similarly, in scenario 2, the query may not return the most recent data because the node with that data may not be queried at all (the other two may).
Keep in mind, these scenarios seem to generally assume you are not writing data at consistently at QUORUM CL so therefore your reads may be inconsistent.
On Tuesday, June 23, 2015, Anuj Wadehra <an...@yahoo.co.in> wrote:
Thanks..So all of us agree that in scenario 1, data would be returned and that was my initial understanding..
Anuj
Sent from Yahoo Mail on Android
From:"Anuj Wadehra" <an...@yahoo.co.in>
Date:Wed, 24 Jun, 2015 at 12:15 am
Subject:Re: Read Consistency
M more confused...Different responses. .Anyone who can explain with 100% surity ?
Thanks
Anuj
Sent from Yahoo Mail on Android
From:"arun sirimalla" <ar...@gmail.com>
Date:Wed, 24 Jun, 2015 at 12:00 am
Subject:Re: Read Consistency
Thanks good to know that.
On Tue, Jun 23, 2015 at 11:27 AM, Philip Thompson <ph...@datastax.com> wrote:
Yes, that is what he means. CL is for how many nodes need to respond, not agree.
On Tue, Jun 23, 2015 at 2:26 PM, arun sirimalla <ar...@gmail.com> wrote:
So do you mean with CL set to QUORUM, if data is only on one node, the query still succeeds.
On Tue, Jun 23, 2015 at 11:21 AM, Philip Thompson <ph...@datastax.com> wrote:
Anuj,
In the first scenario, the data from the single node holding data is returned. The query will not fail if the consistency level is met, even if the read was inconsistent.
On Tue, Jun 23, 2015 at 2:16 PM, Anuj Wadehra <an...@yahoo.co.in> wrote:
Why would it fail and with what Thrift error? What if the data didnt exist on any of the nodes..query wont fail if doesnt find data..
Not convinced..
Sent from Yahoo Mail on Android
From:"arun sirimalla" <ar...@gmail.com>
Date:Tue, 23 Jun, 2015 at 11:39 pm
Subject:Re: Read Consistency
Scenario 1: Read query is fired for a key, data is found on one node and not found on other two nodes who are responsible for the token corresponding to key.
You read query will fail, as it expects to receive data from 2 nodes with RF=3
Scenario 2: Read query is fired and all 3 replicas have different data with different timestamps.
Read query will return the data with most recent timestamp and trigger a read repair in the backend .
On Tue, Jun 23, 2015 at 10:57 AM, Anuj Wadehra <an...@yahoo.co.in> wrote:
Hi,
Need to validate my understanding..
RF=3 , Read CL = Quorum
What would be returned to the client in following scenarios:
Scenario 1: Read query is fired for a key, data is found on one node and not found on other two nodes who are responsible for the token corresponding to key.
Options: no data is returned OR data from the only node having data is returned?
Scenario 2: Read query is fired and all 3 replicas have different data with different timestamps.
Options: data with latest timestamp is returned OR something else???
Thanks
Anuj
Sent from Yahoo Mail on Android
--
Arun
--
Arun
Senior Hadoop/Cassandra Engineer
Cloudwick
2014 Data Impact Award Winner (Cloudera)
http://www.cloudera.com/content/cloudera/en/campaign/data-impact-awards.html
--
Arun
Senior Hadoop/Cassandra Engineer
Cloudwick
2014 Data Impact Award Winner (Cloudera)
http://www.cloudera.com/content/cloudera/en/campaign/data-impact-awards.html
--
Tyler Hobbs
DataStax
Re: Read Consistency
Posted by Tyler Hobbs <ty...@datastax.com>.
>
>
> I think these scenarios are still possible even when we are writing at
> QUORUM ..if we have dropped mutations in our cluster..
> It was very strange in our case ...We had RF=3 and READ/WRITE
> CL=QUORUM..we had dropped mutations for long time but we never faced any
> scenario like scenario 1 when READ went to node 2 and 3 and read did's
> return any data..Any comments on this are welcome??
They are not possible if you write at QUORUM, because QUORUM guarantees
that at least two of the nodes will have the most recent version of the
data. If fewer than two replicas respond successfully (meaning two
replicas dropped mutations), you will get an error on the write.
All of the drivers and cqlsh default to consistency level ONE, so I would
double check that your application is setting the consistency level
correctly.
On Sun, Jun 28, 2015 at 12:55 PM, Anuj Wadehra <an...@yahoo.co.in>
wrote:
> Sorry for typo in your name Owen !!
>
> Anuj
>
> Sent from Yahoo Mail on Android
> <https://overview.mail.yahoo.com/mobile/?.src=Android>
> ------------------------------
> *From*:"Anuj Wadehra" <an...@yahoo.co.in>
> *Date*:Sun, 28 Jun, 2015 at 11:11 pm
> *Subject*:Re: Read Consistency
>
> Agree Owem !! Response in both scenarios would depend on the 2 replicas
> chosen for meeting QUORUM. But, the intent is to get the tricky part of
> scenario 1 answered i.e. when 2 nodes selected are one with and one without
> data.
>
> As per my understanding of Read Path and documentation
> https://wiki.apache.org/cassandra/ArchitectureInternals:
> 1. Data would be read from closest node and digest would be received from
> one more replica.
> 2. If mismatch is found between digest, blocked read happens on same 2
> replicas (not all replicas ..so in scenario 2, if 2 nodes didnt have latest
> data and third node has it ..still stale data would be returned)
>
> I think these scenarios are still possible even when we are writing at
> QUORUM ..if we have dropped mutations in our cluster..
> It was very strange in our case ...We had RF=3 and READ/WRITE
> CL=QUORUM..we had dropped mutations for long time but we never faced any
> scenario like scenario 1 when READ went to node 2 and 3 and read did's
> return any data..Any comments on this are welcome??
>
> Thanks for clarifying further as discussion could have mislead few..
>
> Thanks
> Anuj
>
>
>
> On Sunday, 28 June 2015 6:16 AM, Owen Kim <oh...@gmail.com> wrote:
>
>
> Sorry. I have to jump in and disagree. Data is not guaranteed to retire in
> scenario 1. Since two nodes do not have data and two nodes may be the only
> nodes queried at that CL, the read query may return data or not.
>
> Similarly, in scenario 2, the query may not return the most recent data
> because the node with that data may not be queried at all (the other two
> may).
>
> Keep in mind, these scenarios seem to generally assume you are not writing
> data at consistently at QUORUM CL so therefore your reads may be
> inconsistent.
>
> On Tuesday, June 23, 2015, Anuj Wadehra <an...@yahoo.co.in> wrote:
>
> Thanks..So all of us agree that in scenario 1, data would be returned and
> that was my initial understanding..
>
>
> Anuj
>
>
>
> Sent from Yahoo Mail on Android
> <https://overview.mail.yahoo.com/mobile/?.src=Android>
> ------------------------------
> *From*:"Anuj Wadehra" <an...@yahoo.co.in>
> *Date*:Wed, 24 Jun, 2015 at 12:15 am
> *Subject*:Re: Read Consistency
>
> M more confused...Different responses. .Anyone who can explain with 100%
> surity ?
>
> Thanks
> Anuj
>
>
> Sent from Yahoo Mail on Android
> <https://overview.mail.yahoo.com/mobile/?.src=Android>
> ------------------------------
> *From*:"arun sirimalla" <ar...@gmail.com>
> *Date*:Wed, 24 Jun, 2015 at 12:00 am
> *Subject*:Re: Read Consistency
>
>
> Thanks good to know that.
>
> On Tue, Jun 23, 2015 at 11:27 AM, Philip Thompson <
> philip.thompson@datastax.com> wrote:
>
> Yes, that is what he means. CL is for how many nodes need to respond, not
> agree.
>
> On Tue, Jun 23, 2015 at 2:26 PM, arun sirimalla <ar...@gmail.com>
> wrote:
>
> So do you mean with CL set to QUORUM, if data is only on one node, the
> query still succeeds.
>
> On Tue, Jun 23, 2015 at 11:21 AM, Philip Thompson <
> philip.thompson@datastax.com> wrote:
>
> Anuj,
>
> In the first scenario, the data from the single node holding data is
> returned. The query will not fail if the consistency level is met, even if
> the read was inconsistent.
>
> On Tue, Jun 23, 2015 at 2:16 PM, Anuj Wadehra <an...@yahoo.co.in>
> wrote:
>
> Why would it fail and with what Thrift error? What if the data didnt exist
> on any of the nodes..query wont fail if doesnt find data..
>
> Not convinced..
>
> Sent from Yahoo Mail on Android
> <https://overview.mail.yahoo.com/mobile/?.src=Android>
> ------------------------------
> *From*:"arun sirimalla" <ar...@gmail.com>
> *Date*:Tue, 23 Jun, 2015 at 11:39 pm
> *Subject*:Re: Read Consistency
>
> Scenario 1: Read query is fired for a key, data is found on one node and
> not found on other two nodes who are responsible for the token
> corresponding to key.
>
> You read query will fail, as it expects to receive data from 2 nodes with
> RF=3
>
>
> Scenario 2: Read query is fired and all 3 replicas have different data
> with different timestamps.
>
> Read query will return the data with most recent timestamp and trigger a
> read repair in the backend .
>
> On Tue, Jun 23, 2015 at 10:57 AM, Anuj Wadehra <an...@yahoo.co.in>
> wrote:
>
> Hi,
>
> Need to validate my understanding..
>
> RF=3 , Read CL = Quorum
>
> What would be returned to the client in following scenarios:
>
> Scenario 1: Read query is fired for a key, data is found on one node and
> not found on other two nodes who are responsible for the token
> corresponding to key.
>
> Options: no data is returned OR data from the only node having data is
> returned?
>
> Scenario 2: Read query is fired and all 3 replicas have different data
> with different timestamps.
>
> Options: data with latest timestamp is returned OR something else???
>
> Thanks
> Anuj
>
> Sent from Yahoo Mail on Android
> <https://overview.mail.yahoo.com/mobile/?.src=Android>
>
>
>
>
> --
> Arun
>
>
>
>
>
> --
> Arun
> Senior Hadoop/Cassandra Engineer
> Cloudwick
>
>
> 2014 Data Impact Award Winner (Cloudera)
>
> http://www.cloudera.com/content/cloudera/en/campaign/data-impact-awards.html
>
>
>
>
>
> --
> Arun
> Senior Hadoop/Cassandra Engineer
> Cloudwick
>
>
> 2014 Data Impact Award Winner (Cloudera)
>
> http://www.cloudera.com/content/cloudera/en/campaign/data-impact-awards.html
>
>
>
>
--
Tyler Hobbs
DataStax <http://datastax.com/>
Re: Read Consistency
Posted by Anuj Wadehra <an...@yahoo.co.in>.
Sorry for typo in your name Owen !!
Anuj
Sent from Yahoo Mail on Android
From:"Anuj Wadehra" <an...@yahoo.co.in>
Date:Sun, 28 Jun, 2015 at 11:11 pm
Subject:Re: Read Consistency
Agree Owem !! Response in both scenarios would depend on the 2 replicas chosen for meeting QUORUM. But, the intent is to get the tricky part of scenario 1 answered i.e. when 2 nodes selected are one with and one without data.
As per my understanding of Read Path and documentation https://wiki.apache.org/cassandra/ArchitectureInternals:
1. Data would be read from closest node and digest would be received from one more replica.
2. If mismatch is found between digest, blocked read happens on same 2 replicas (not all replicas ..so in scenario 2, if 2 nodes didnt have latest data and third node has it ..still stale data would be returned)
I think these scenarios are still possible even when we are writing at QUORUM ..if we have dropped mutations in our cluster..
It was very strange in our case ...We had RF=3 and READ/WRITE CL=QUORUM..we had dropped mutations for long time but we never faced any scenario like scenario 1 when READ went to node 2 and 3 and read did's return any data..Any comments on this are welcome??
Thanks for clarifying further as discussion could have mislead few..
Thanks
Anuj
On Sunday, 28 June 2015 6:16 AM, Owen Kim <oh...@gmail.com> wrote:
Sorry. I have to jump in and disagree. Data is not guaranteed to retire in scenario 1. Since two nodes do not have data and two nodes may be the only nodes queried at that CL, the read query may return data or not.
Similarly, in scenario 2, the query may not return the most recent data because the node with that data may not be queried at all (the other two may).
Keep in mind, these scenarios seem to generally assume you are not writing data at consistently at QUORUM CL so therefore your reads may be inconsistent.
On Tuesday, June 23, 2015, Anuj Wadehra <an...@yahoo.co.in> wrote:
Thanks..So all of us agree that in scenario 1, data would be returned and that was my initial understanding..
Anuj
Sent from Yahoo Mail on Android
From:"Anuj Wadehra" <an...@yahoo.co.in>
Date:Wed, 24 Jun, 2015 at 12:15 am
Subject:Re: Read Consistency
M more confused...Different responses. .Anyone who can explain with 100% surity ?
Thanks
Anuj
Sent from Yahoo Mail on Android
From:"arun sirimalla" <ar...@gmail.com>
Date:Wed, 24 Jun, 2015 at 12:00 am
Subject:Re: Read Consistency
Thanks good to know that.
On Tue, Jun 23, 2015 at 11:27 AM, Philip Thompson <ph...@datastax.com> wrote:
Yes, that is what he means. CL is for how many nodes need to respond, not agree.
On Tue, Jun 23, 2015 at 2:26 PM, arun sirimalla <ar...@gmail.com> wrote:
So do you mean with CL set to QUORUM, if data is only on one node, the query still succeeds.
On Tue, Jun 23, 2015 at 11:21 AM, Philip Thompson <ph...@datastax.com> wrote:
Anuj,
In the first scenario, the data from the single node holding data is returned. The query will not fail if the consistency level is met, even if the read was inconsistent.
On Tue, Jun 23, 2015 at 2:16 PM, Anuj Wadehra <an...@yahoo.co.in> wrote:
Why would it fail and with what Thrift error? What if the data didnt exist on any of the nodes..query wont fail if doesnt find data..
Not convinced..
Sent from Yahoo Mail on Android
From:"arun sirimalla" <ar...@gmail.com>
Date:Tue, 23 Jun, 2015 at 11:39 pm
Subject:Re: Read Consistency
Scenario 1: Read query is fired for a key, data is found on one node and not found on other two nodes who are responsible for the token corresponding to key.
You read query will fail, as it expects to receive data from 2 nodes with RF=3
Scenario 2: Read query is fired and all 3 replicas have different data with different timestamps.
Read query will return the data with most recent timestamp and trigger a read repair in the backend .
On Tue, Jun 23, 2015 at 10:57 AM, Anuj Wadehra <an...@yahoo.co.in> wrote:
Hi,
Need to validate my understanding..
RF=3 , Read CL = Quorum
What would be returned to the client in following scenarios:
Scenario 1: Read query is fired for a key, data is found on one node and not found on other two nodes who are responsible for the token corresponding to key.
Options: no data is returned OR data from the only node having data is returned?
Scenario 2: Read query is fired and all 3 replicas have different data with different timestamps.
Options: data with latest timestamp is returned OR something else???
Thanks
Anuj
Sent from Yahoo Mail on Android
--
Arun
--
Arun
Senior Hadoop/Cassandra Engineer
Cloudwick
2014 Data Impact Award Winner (Cloudera)
http://www.cloudera.com/content/cloudera/en/campaign/data-impact-awards.html
--
Arun
Senior Hadoop/Cassandra Engineer
Cloudwick
2014 Data Impact Award Winner (Cloudera)
http://www.cloudera.com/content/cloudera/en/campaign/data-impact-awards.html
Re: Read Consistency
Posted by Anuj Wadehra <an...@yahoo.co.in>.
Agree Owem !! Response in both scenarios would depend on the 2 replicas chosen for meeting QUORUM. But, the intent is to get the tricky part of scenario 1 answered i.e. when 2 nodes selected are one with and one without data.
As per my understanding of Read Path and documentation https://wiki.apache.org/cassandra/ArchitectureInternals:1. Data would be read from closest node and digest would be received from one more replica.2. If mismatch is found between digest, blocked read happens on same 2 replicas (not all replicas ..so in scenario 2, if 2 nodes didnt have latest data and third node has it ..still stale data would be returned)
I think these scenarios are still possible even when we are writing at QUORUM ..if we have dropped mutations in our cluster..It was very strange in our case ...We had RF=3 and READ/WRITE CL=QUORUM..we had dropped mutations for long time but we never faced any scenario like scenario 1 when READ went to node 2 and 3 and read did's return any data..Any comments on this are welcome??
Thanks for clarifying further as discussion could have mislead few..
ThanksAnuj
On Sunday, 28 June 2015 6:16 AM, Owen Kim <oh...@gmail.com> wrote:
Sorry. I have to jump in and disagree. Data is not guaranteed to retire in scenario 1. Since two nodes do not have data and two nodes may be the only nodes queried at that CL, the read query may return data or not.
Similarly, in scenario 2, the query may not return the most recent data because the node with that data may not be queried at all (the other two may).
Keep in mind, these scenarios seem to generally assume you are not writing data at consistently at QUORUM CL so therefore your reads may be inconsistent.
On Tuesday, June 23, 2015, Anuj Wadehra <an...@yahoo.co.in> wrote:
| Thanks..So all of us agree that in scenario 1, data would be returned and that was my initial understanding..
Anuj
Sent from Yahoo Mail on Android
| From:"Anuj Wadehra" <an...@yahoo.co.in>
Date:Wed, 24 Jun, 2015 at 12:15 am
Subject:Re: Read Consistency
| M more confused...Different responses. .Anyone who can explain with 100% surity ?
ThanksAnuj
Sent from Yahoo Mail on Android
| From:"arun sirimalla" <ar...@gmail.com>
Date:Wed, 24 Jun, 2015 at 12:00 am
Subject:Re: Read Consistency
Thanks good to know that.
On Tue, Jun 23, 2015 at 11:27 AM, Philip Thompson <ph...@datastax.com> wrote:
Yes, that is what he means. CL is for how many nodes need to respond, not agree.
On Tue, Jun 23, 2015 at 2:26 PM, arun sirimalla <ar...@gmail.com> wrote:
So do you mean with CL set to QUORUM, if data is only on one node, the query still succeeds.
On Tue, Jun 23, 2015 at 11:21 AM, Philip Thompson <ph...@datastax.com> wrote:
Anuj,
In the first scenario, the data from the single node holding data is returned. The query will not fail if the consistency level is met, even if the read was inconsistent.
On Tue, Jun 23, 2015 at 2:16 PM, Anuj Wadehra <an...@yahoo.co.in> wrote:
| Why would it fail and with what Thrift error? What if the data didnt exist on any of the nodes..query wont fail if doesnt find data..
Not convinced..
Sent from Yahoo Mail on Android
| From:"arun sirimalla" <ar...@gmail.com>
Date:Tue, 23 Jun, 2015 at 11:39 pm
Subject:Re: Read Consistency
Scenario 1: Read query is fired for a key, data is found on one node and not found on other two nodes who are responsible for the token corresponding to key.
You read query will fail, as it expects to receive data from 2 nodes with RF=3
Scenario 2: Read query is fired and all 3 replicas have different data with different timestamps.
Read query will return the data with most recent timestamp and trigger a read repair in the backend .
On Tue, Jun 23, 2015 at 10:57 AM, Anuj Wadehra <an...@yahoo.co.in> wrote:
| Hi,
Need to validate my understanding..
RF=3 , Read CL = Quorum
What would be returned to the client in following scenarios:
Scenario 1: Read query is fired for a key, data is found on one node and not found on other two nodes who are responsible for the token corresponding to key.
Options: no data is returned OR data from the only node having data is returned?
Scenario 2: Read query is fired and all 3 replicas have different data with different timestamps.
Options: data with latest timestamp is returned OR something else???
ThanksAnuj
Sent from Yahoo Mail on Android |
--
Arun |
|
--
Arun Senior Hadoop/Cassandra EngineerCloudwick
2014 Data Impact Award Winner (Cloudera)http://www.cloudera.com/content/cloudera/en/campaign/data-impact-awards.html
--
Arun Senior Hadoop/Cassandra EngineerCloudwick
2014 Data Impact Award Winner (Cloudera)http://www.cloudera.com/content/cloudera/en/campaign/data-impact-awards.html
|
|
|
|
Re: Read Consistency
Posted by Owen Kim <oh...@gmail.com>.
Sorry. I have to jump in and disagree. Data is not guaranteed to retire in
scenario 1. Since two nodes do not have data and two nodes may be the only
nodes queried at that CL, the read query may return data or not.
Similarly, in scenario 2, the query may not return the most recent data
because the node with that data may not be queried at all (the other two
may).
Keep in mind, these scenarios seem to generally assume you are not writing
data at consistently at QUORUM CL so therefore your reads may be
inconsistent.
On Tuesday, June 23, 2015, Anuj Wadehra <an...@yahoo.co.in> wrote:
> Thanks..So all of us agree that in scenario 1, data would be returned and
> that was my initial understanding..
>
>
> Anuj
>
>
>
> Sent from Yahoo Mail on Android
> <https://overview.mail.yahoo.com/mobile/?.src=Android>
> ------------------------------
> *From*:"Anuj Wadehra" <anujw_2003@yahoo.co.in
> <javascript:_e(%7B%7D,'cvml','anujw_2003@yahoo.co.in');>>
> *Date*:Wed, 24 Jun, 2015 at 12:15 am
> *Subject*:Re: Read Consistency
>
> M more confused...Different responses. .Anyone who can explain with 100%
> surity ?
>
> Thanks
> Anuj
>
>
> Sent from Yahoo Mail on Android
> <https://overview.mail.yahoo.com/mobile/?.src=Android>
> ------------------------------
> *From*:"arun sirimalla" <arunsirik@gmail.com
> <javascript:_e(%7B%7D,'cvml','arunsirik@gmail.com');>>
> *Date*:Wed, 24 Jun, 2015 at 12:00 am
> *Subject*:Re: Read Consistency
>
>
> Thanks good to know that.
>
> On Tue, Jun 23, 2015 at 11:27 AM, Philip Thompson <
> philip.thompson@datastax.com> wrote:
>
>> Yes, that is what he means. CL is for how many nodes need to respond, not
>> agree.
>>
>> On Tue, Jun 23, 2015 at 2:26 PM, arun sirimalla <ar...@gmail.com>
>> wrote:
>>
>>> So do you mean with CL set to QUORUM, if data is only on one node, the
>>> query still succeeds.
>>>
>>> On Tue, Jun 23, 2015 at 11:21 AM, Philip Thompson <
>>> philip.thompson@datastax.com> wrote:
>>>
>>>> Anuj,
>>>>
>>>> In the first scenario, the data from the single node holding data is
>>>> returned. The query will not fail if the consistency level is met, even if
>>>> the read was inconsistent.
>>>>
>>>> On Tue, Jun 23, 2015 at 2:16 PM, Anuj Wadehra <an...@yahoo.co.in>
>>>> wrote:
>>>>
>>>>> Why would it fail and with what Thrift error? What if the data didnt
>>>>> exist on any of the nodes..query wont fail if doesnt find data..
>>>>>
>>>>> Not convinced..
>>>>>
>>>>> Sent from Yahoo Mail on Android
>>>>> <https://overview.mail.yahoo.com/mobile/?.src=Android>
>>>>> ------------------------------
>>>>> *From*:"arun sirimalla" <ar...@gmail.com>
>>>>> *Date*:Tue, 23 Jun, 2015 at 11:39 pm
>>>>> *Subject*:Re: Read Consistency
>>>>>
>>>>> Scenario 1: Read query is fired for a key, data is found on one node
>>>>> and not found on other two nodes who are responsible for the token
>>>>> corresponding to key.
>>>>>
>>>>> You read query will fail, as it expects to receive data from 2 nodes
>>>>> with RF=3
>>>>>
>>>>>
>>>>> Scenario 2: Read query is fired and all 3 replicas have different data
>>>>> with different timestamps.
>>>>>
>>>>> Read query will return the data with most recent timestamp and trigger
>>>>> a read repair in the backend .
>>>>>
>>>>> On Tue, Jun 23, 2015 at 10:57 AM, Anuj Wadehra <anujw_2003@yahoo.co.in
>>>>> > wrote:
>>>>>
>>>>>> Hi,
>>>>>>
>>>>>> Need to validate my understanding..
>>>>>>
>>>>>> RF=3 , Read CL = Quorum
>>>>>>
>>>>>> What would be returned to the client in following scenarios:
>>>>>>
>>>>>> Scenario 1: Read query is fired for a key, data is found on one node
>>>>>> and not found on other two nodes who are responsible for the token
>>>>>> corresponding to key.
>>>>>>
>>>>>> Options: no data is returned OR data from the only node having data
>>>>>> is returned?
>>>>>>
>>>>>> Scenario 2: Read query is fired and all 3 replicas have different
>>>>>> data with different timestamps.
>>>>>>
>>>>>> Options: data with latest timestamp is returned OR something else???
>>>>>>
>>>>>> Thanks
>>>>>> Anuj
>>>>>>
>>>>>> Sent from Yahoo Mail on Android
>>>>>> <https://overview.mail.yahoo.com/mobile/?.src=Android>
>>>>>>
>>>>>
>>>>>
>>>>>
>>>>> --
>>>>> Arun
>>>>>
>>>>
>>>>
>>>
>>>
>>> --
>>> Arun
>>> Senior Hadoop/Cassandra Engineer
>>> Cloudwick
>>>
>>>
>>> 2014 Data Impact Award Winner (Cloudera)
>>>
>>> http://www.cloudera.com/content/cloudera/en/campaign/data-impact-awards.html
>>>
>>>
>>
>
>
> --
> Arun
> Senior Hadoop/Cassandra Engineer
> Cloudwick
>
>
> 2014 Data Impact Award Winner (Cloudera)
>
> http://www.cloudera.com/content/cloudera/en/campaign/data-impact-awards.html
>
>
Re: Read Consistency
Posted by Anuj Wadehra <an...@yahoo.co.in>.
Thanks..So all of us agree that in scenario 1, data would be returned and that was my initial understanding..
Anuj
Sent from Yahoo Mail on Android
From:"Anuj Wadehra" <an...@yahoo.co.in>
Date:Wed, 24 Jun, 2015 at 12:15 am
Subject:Re: Read Consistency
M more confused...Different responses. .Anyone who can explain with 100% surity ?
Thanks
Anuj
Sent from Yahoo Mail on Android
From:"arun sirimalla" <ar...@gmail.com>
Date:Wed, 24 Jun, 2015 at 12:00 am
Subject:Re: Read Consistency
Thanks good to know that.
On Tue, Jun 23, 2015 at 11:27 AM, Philip Thompson <ph...@datastax.com> wrote:
Yes, that is what he means. CL is for how many nodes need to respond, not agree.
On Tue, Jun 23, 2015 at 2:26 PM, arun sirimalla <ar...@gmail.com> wrote:
So do you mean with CL set to QUORUM, if data is only on one node, the query still succeeds.
On Tue, Jun 23, 2015 at 11:21 AM, Philip Thompson <ph...@datastax.com> wrote:
Anuj,
In the first scenario, the data from the single node holding data is returned. The query will not fail if the consistency level is met, even if the read was inconsistent.
On Tue, Jun 23, 2015 at 2:16 PM, Anuj Wadehra <an...@yahoo.co.in> wrote:
Why would it fail and with what Thrift error? What if the data didnt exist on any of the nodes..query wont fail if doesnt find data..
Not convinced..
Sent from Yahoo Mail on Android
From:"arun sirimalla" <ar...@gmail.com>
Date:Tue, 23 Jun, 2015 at 11:39 pm
Subject:Re: Read Consistency
Scenario 1: Read query is fired for a key, data is found on one node and not found on other two nodes who are responsible for the token corresponding to key.
You read query will fail, as it expects to receive data from 2 nodes with RF=3
Scenario 2: Read query is fired and all 3 replicas have different data with different timestamps.
Read query will return the data with most recent timestamp and trigger a read repair in the backend .
On Tue, Jun 23, 2015 at 10:57 AM, Anuj Wadehra <an...@yahoo.co.in> wrote:
Hi,
Need to validate my understanding..
RF=3 , Read CL = Quorum
What would be returned to the client in following scenarios:
Scenario 1: Read query is fired for a key, data is found on one node and not found on other two nodes who are responsible for the token corresponding to key.
Options: no data is returned OR data from the only node having data is returned?
Scenario 2: Read query is fired and all 3 replicas have different data with different timestamps.
Options: data with latest timestamp is returned OR something else???
Thanks
Anuj
Sent from Yahoo Mail on Android
--
Arun
--
Arun
Senior Hadoop/Cassandra Engineer
Cloudwick
2014 Data Impact Award Winner (Cloudera)
http://www.cloudera.com/content/cloudera/en/campaign/data-impact-awards.html
--
Arun
Senior Hadoop/Cassandra Engineer
Cloudwick
2014 Data Impact Award Winner (Cloudera)
http://www.cloudera.com/content/cloudera/en/campaign/data-impact-awards.html
Re: Read Consistency
Posted by Anuj Wadehra <an...@yahoo.co.in>.
M more confused...Different responses. .Anyone who can explain with 100% surity ?
Thanks
Anuj
Sent from Yahoo Mail on Android
From:"arun sirimalla" <ar...@gmail.com>
Date:Wed, 24 Jun, 2015 at 12:00 am
Subject:Re: Read Consistency
Thanks good to know that.
On Tue, Jun 23, 2015 at 11:27 AM, Philip Thompson <ph...@datastax.com> wrote:
Yes, that is what he means. CL is for how many nodes need to respond, not agree.
On Tue, Jun 23, 2015 at 2:26 PM, arun sirimalla <ar...@gmail.com> wrote:
So do you mean with CL set to QUORUM, if data is only on one node, the query still succeeds.
On Tue, Jun 23, 2015 at 11:21 AM, Philip Thompson <ph...@datastax.com> wrote:
Anuj,
In the first scenario, the data from the single node holding data is returned. The query will not fail if the consistency level is met, even if the read was inconsistent.
On Tue, Jun 23, 2015 at 2:16 PM, Anuj Wadehra <an...@yahoo.co.in> wrote:
Why would it fail and with what Thrift error? What if the data didnt exist on any of the nodes..query wont fail if doesnt find data..
Not convinced..
Sent from Yahoo Mail on Android
From:"arun sirimalla" <ar...@gmail.com>
Date:Tue, 23 Jun, 2015 at 11:39 pm
Subject:Re: Read Consistency
Scenario 1: Read query is fired for a key, data is found on one node and not found on other two nodes who are responsible for the token corresponding to key.
You read query will fail, as it expects to receive data from 2 nodes with RF=3
Scenario 2: Read query is fired and all 3 replicas have different data with different timestamps.
Read query will return the data with most recent timestamp and trigger a read repair in the backend .
On Tue, Jun 23, 2015 at 10:57 AM, Anuj Wadehra <an...@yahoo.co.in> wrote:
Hi,
Need to validate my understanding..
RF=3 , Read CL = Quorum
What would be returned to the client in following scenarios:
Scenario 1: Read query is fired for a key, data is found on one node and not found on other two nodes who are responsible for the token corresponding to key.
Options: no data is returned OR data from the only node having data is returned?
Scenario 2: Read query is fired and all 3 replicas have different data with different timestamps.
Options: data with latest timestamp is returned OR something else???
Thanks
Anuj
Sent from Yahoo Mail on Android
--
Arun
--
Arun
Senior Hadoop/Cassandra Engineer
Cloudwick
2014 Data Impact Award Winner (Cloudera)
http://www.cloudera.com/content/cloudera/en/campaign/data-impact-awards.html
--
Arun
Senior Hadoop/Cassandra Engineer
Cloudwick
2014 Data Impact Award Winner (Cloudera)
http://www.cloudera.com/content/cloudera/en/campaign/data-impact-awards.html
Re: Read Consistency
Posted by arun sirimalla <ar...@gmail.com>.
Thanks good to know that.
On Tue, Jun 23, 2015 at 11:27 AM, Philip Thompson <
philip.thompson@datastax.com> wrote:
> Yes, that is what he means. CL is for how many nodes need to respond, not
> agree.
>
> On Tue, Jun 23, 2015 at 2:26 PM, arun sirimalla <ar...@gmail.com>
> wrote:
>
>> So do you mean with CL set to QUORUM, if data is only on one node, the
>> query still succeeds.
>>
>> On Tue, Jun 23, 2015 at 11:21 AM, Philip Thompson <
>> philip.thompson@datastax.com> wrote:
>>
>>> Anuj,
>>>
>>> In the first scenario, the data from the single node holding data is
>>> returned. The query will not fail if the consistency level is met, even if
>>> the read was inconsistent.
>>>
>>> On Tue, Jun 23, 2015 at 2:16 PM, Anuj Wadehra <an...@yahoo.co.in>
>>> wrote:
>>>
>>>> Why would it fail and with what Thrift error? What if the data didnt
>>>> exist on any of the nodes..query wont fail if doesnt find data..
>>>>
>>>> Not convinced..
>>>>
>>>> Sent from Yahoo Mail on Android
>>>> <https://overview.mail.yahoo.com/mobile/?.src=Android>
>>>> ------------------------------
>>>> *From*:"arun sirimalla" <ar...@gmail.com>
>>>> *Date*:Tue, 23 Jun, 2015 at 11:39 pm
>>>> *Subject*:Re: Read Consistency
>>>>
>>>> Scenario 1: Read query is fired for a key, data is found on one node
>>>> and not found on other two nodes who are responsible for the token
>>>> corresponding to key.
>>>>
>>>> You read query will fail, as it expects to receive data from 2 nodes
>>>> with RF=3
>>>>
>>>>
>>>> Scenario 2: Read query is fired and all 3 replicas have different data
>>>> with different timestamps.
>>>>
>>>> Read query will return the data with most recent timestamp and trigger
>>>> a read repair in the backend .
>>>>
>>>> On Tue, Jun 23, 2015 at 10:57 AM, Anuj Wadehra <an...@yahoo.co.in>
>>>> wrote:
>>>>
>>>>> Hi,
>>>>>
>>>>> Need to validate my understanding..
>>>>>
>>>>> RF=3 , Read CL = Quorum
>>>>>
>>>>> What would be returned to the client in following scenarios:
>>>>>
>>>>> Scenario 1: Read query is fired for a key, data is found on one node
>>>>> and not found on other two nodes who are responsible for the token
>>>>> corresponding to key.
>>>>>
>>>>> Options: no data is returned OR data from the only node having data is
>>>>> returned?
>>>>>
>>>>> Scenario 2: Read query is fired and all 3 replicas have different data
>>>>> with different timestamps.
>>>>>
>>>>> Options: data with latest timestamp is returned OR something else???
>>>>>
>>>>> Thanks
>>>>> Anuj
>>>>>
>>>>> Sent from Yahoo Mail on Android
>>>>> <https://overview.mail.yahoo.com/mobile/?.src=Android>
>>>>>
>>>>
>>>>
>>>>
>>>> --
>>>> Arun
>>>>
>>>
>>>
>>
>>
>> --
>> Arun
>> Senior Hadoop/Cassandra Engineer
>> Cloudwick
>>
>>
>> 2014 Data Impact Award Winner (Cloudera)
>>
>> http://www.cloudera.com/content/cloudera/en/campaign/data-impact-awards.html
>>
>>
>
--
Arun
Senior Hadoop/Cassandra Engineer
Cloudwick
2014 Data Impact Award Winner (Cloudera)
http://www.cloudera.com/content/cloudera/en/campaign/data-impact-awards.html
Re: Read Consistency
Posted by Philip Thompson <ph...@datastax.com>.
Yes, that is what he means. CL is for how many nodes need to respond, not
agree.
On Tue, Jun 23, 2015 at 2:26 PM, arun sirimalla <ar...@gmail.com> wrote:
> So do you mean with CL set to QUORUM, if data is only on one node, the
> query still succeeds.
>
> On Tue, Jun 23, 2015 at 11:21 AM, Philip Thompson <
> philip.thompson@datastax.com> wrote:
>
>> Anuj,
>>
>> In the first scenario, the data from the single node holding data is
>> returned. The query will not fail if the consistency level is met, even if
>> the read was inconsistent.
>>
>> On Tue, Jun 23, 2015 at 2:16 PM, Anuj Wadehra <an...@yahoo.co.in>
>> wrote:
>>
>>> Why would it fail and with what Thrift error? What if the data didnt
>>> exist on any of the nodes..query wont fail if doesnt find data..
>>>
>>> Not convinced..
>>>
>>> Sent from Yahoo Mail on Android
>>> <https://overview.mail.yahoo.com/mobile/?.src=Android>
>>> ------------------------------
>>> *From*:"arun sirimalla" <ar...@gmail.com>
>>> *Date*:Tue, 23 Jun, 2015 at 11:39 pm
>>> *Subject*:Re: Read Consistency
>>>
>>> Scenario 1: Read query is fired for a key, data is found on one node and
>>> not found on other two nodes who are responsible for the token
>>> corresponding to key.
>>>
>>> You read query will fail, as it expects to receive data from 2 nodes
>>> with RF=3
>>>
>>>
>>> Scenario 2: Read query is fired and all 3 replicas have different data
>>> with different timestamps.
>>>
>>> Read query will return the data with most recent timestamp and trigger a
>>> read repair in the backend .
>>>
>>> On Tue, Jun 23, 2015 at 10:57 AM, Anuj Wadehra <an...@yahoo.co.in>
>>> wrote:
>>>
>>>> Hi,
>>>>
>>>> Need to validate my understanding..
>>>>
>>>> RF=3 , Read CL = Quorum
>>>>
>>>> What would be returned to the client in following scenarios:
>>>>
>>>> Scenario 1: Read query is fired for a key, data is found on one node
>>>> and not found on other two nodes who are responsible for the token
>>>> corresponding to key.
>>>>
>>>> Options: no data is returned OR data from the only node having data is
>>>> returned?
>>>>
>>>> Scenario 2: Read query is fired and all 3 replicas have different data
>>>> with different timestamps.
>>>>
>>>> Options: data with latest timestamp is returned OR something else???
>>>>
>>>> Thanks
>>>> Anuj
>>>>
>>>> Sent from Yahoo Mail on Android
>>>> <https://overview.mail.yahoo.com/mobile/?.src=Android>
>>>>
>>>
>>>
>>>
>>> --
>>> Arun
>>>
>>
>>
>
>
> --
> Arun
> Senior Hadoop/Cassandra Engineer
> Cloudwick
>
>
> 2014 Data Impact Award Winner (Cloudera)
>
> http://www.cloudera.com/content/cloudera/en/campaign/data-impact-awards.html
>
>
Re: Read Consistency
Posted by arun sirimalla <ar...@gmail.com>.
So do you mean with CL set to QUORUM, if data is only on one node, the
query still succeeds.
On Tue, Jun 23, 2015 at 11:21 AM, Philip Thompson <
philip.thompson@datastax.com> wrote:
> Anuj,
>
> In the first scenario, the data from the single node holding data is
> returned. The query will not fail if the consistency level is met, even if
> the read was inconsistent.
>
> On Tue, Jun 23, 2015 at 2:16 PM, Anuj Wadehra <an...@yahoo.co.in>
> wrote:
>
>> Why would it fail and with what Thrift error? What if the data didnt
>> exist on any of the nodes..query wont fail if doesnt find data..
>>
>> Not convinced..
>>
>> Sent from Yahoo Mail on Android
>> <https://overview.mail.yahoo.com/mobile/?.src=Android>
>> ------------------------------
>> *From*:"arun sirimalla" <ar...@gmail.com>
>> *Date*:Tue, 23 Jun, 2015 at 11:39 pm
>> *Subject*:Re: Read Consistency
>>
>> Scenario 1: Read query is fired for a key, data is found on one node and
>> not found on other two nodes who are responsible for the token
>> corresponding to key.
>>
>> You read query will fail, as it expects to receive data from 2 nodes with
>> RF=3
>>
>>
>> Scenario 2: Read query is fired and all 3 replicas have different data
>> with different timestamps.
>>
>> Read query will return the data with most recent timestamp and trigger a
>> read repair in the backend .
>>
>> On Tue, Jun 23, 2015 at 10:57 AM, Anuj Wadehra <an...@yahoo.co.in>
>> wrote:
>>
>>> Hi,
>>>
>>> Need to validate my understanding..
>>>
>>> RF=3 , Read CL = Quorum
>>>
>>> What would be returned to the client in following scenarios:
>>>
>>> Scenario 1: Read query is fired for a key, data is found on one node and
>>> not found on other two nodes who are responsible for the token
>>> corresponding to key.
>>>
>>> Options: no data is returned OR data from the only node having data is
>>> returned?
>>>
>>> Scenario 2: Read query is fired and all 3 replicas have different data
>>> with different timestamps.
>>>
>>> Options: data with latest timestamp is returned OR something else???
>>>
>>> Thanks
>>> Anuj
>>>
>>> Sent from Yahoo Mail on Android
>>> <https://overview.mail.yahoo.com/mobile/?.src=Android>
>>>
>>
>>
>>
>> --
>> Arun
>>
>
>
--
Arun
Senior Hadoop/Cassandra Engineer
Cloudwick
2014 Data Impact Award Winner (Cloudera)
http://www.cloudera.com/content/cloudera/en/campaign/data-impact-awards.html
Re: Read Consistency
Posted by Philip Thompson <ph...@datastax.com>.
Anuj,
In the first scenario, the data from the single node holding data is
returned. The query will not fail if the consistency level is met, even if
the read was inconsistent.
On Tue, Jun 23, 2015 at 2:16 PM, Anuj Wadehra <an...@yahoo.co.in>
wrote:
> Why would it fail and with what Thrift error? What if the data didnt exist
> on any of the nodes..query wont fail if doesnt find data..
>
> Not convinced..
>
> Sent from Yahoo Mail on Android
> <https://overview.mail.yahoo.com/mobile/?.src=Android>
> ------------------------------
> *From*:"arun sirimalla" <ar...@gmail.com>
> *Date*:Tue, 23 Jun, 2015 at 11:39 pm
> *Subject*:Re: Read Consistency
>
> Scenario 1: Read query is fired for a key, data is found on one node and
> not found on other two nodes who are responsible for the token
> corresponding to key.
>
> You read query will fail, as it expects to receive data from 2 nodes with
> RF=3
>
>
> Scenario 2: Read query is fired and all 3 replicas have different data
> with different timestamps.
>
> Read query will return the data with most recent timestamp and trigger a
> read repair in the backend .
>
> On Tue, Jun 23, 2015 at 10:57 AM, Anuj Wadehra <an...@yahoo.co.in>
> wrote:
>
>> Hi,
>>
>> Need to validate my understanding..
>>
>> RF=3 , Read CL = Quorum
>>
>> What would be returned to the client in following scenarios:
>>
>> Scenario 1: Read query is fired for a key, data is found on one node and
>> not found on other two nodes who are responsible for the token
>> corresponding to key.
>>
>> Options: no data is returned OR data from the only node having data is
>> returned?
>>
>> Scenario 2: Read query is fired and all 3 replicas have different data
>> with different timestamps.
>>
>> Options: data with latest timestamp is returned OR something else???
>>
>> Thanks
>> Anuj
>>
>> Sent from Yahoo Mail on Android
>> <https://overview.mail.yahoo.com/mobile/?.src=Android>
>>
>
>
>
> --
> Arun
>
Re: Read Consistency
Posted by Alain RODRIGUEZ <ar...@gmail.com>.
Btw, Hope you'll find the answers you could not ask in today online lesson
;-).
C*heers
2015-06-23 20:22 GMT+02:00 Alain RODRIGUEZ <ar...@gmail.com>:
> Hi,
>
> I do not agree with Scenario 1 result Arun,
>
> The 2 nodes don't have the data yet are available. IMHO what happens next
> i a slow read since it will have to perform read repair and coordinator
> will send back the result and an 'OK' message.Consistency is not met when
> nor enough nodes were up.
>
> Agreed on scenario 2. I would add that one repair will be synchronous and
> mandatory while the second depends on your read repair chance parameter on
> this table and is async.
>
> C*heers
>
> 2015-06-23 20:16 GMT+02:00 Anuj Wadehra <an...@yahoo.co.in>:
>
>> Why would it fail and with what Thrift error? What if the data didnt
>> exist on any of the nodes..query wont fail if doesnt find data..
>>
>> Not convinced..
>>
>> Sent from Yahoo Mail on Android
>> <https://overview.mail.yahoo.com/mobile/?.src=Android>
>> ------------------------------
>> *From*:"arun sirimalla" <ar...@gmail.com>
>> *Date*:Tue, 23 Jun, 2015 at 11:39 pm
>> *Subject*:Re: Read Consistency
>>
>> Scenario 1: Read query is fired for a key, data is found on one node and
>> not found on other two nodes who are responsible for the token
>> corresponding to key.
>>
>> You read query will fail, as it expects to receive data from 2 nodes with
>> RF=3
>>
>>
>> Scenario 2: Read query is fired and all 3 replicas have different data
>> with different timestamps.
>>
>> Read query will return the data with most recent timestamp and trigger a
>> read repair in the backend .
>>
>> On Tue, Jun 23, 2015 at 10:57 AM, Anuj Wadehra <an...@yahoo.co.in>
>> wrote:
>>
>>> Hi,
>>>
>>> Need to validate my understanding..
>>>
>>> RF=3 , Read CL = Quorum
>>>
>>> What would be returned to the client in following scenarios:
>>>
>>> Scenario 1: Read query is fired for a key, data is found on one node and
>>> not found on other two nodes who are responsible for the token
>>> corresponding to key.
>>>
>>> Options: no data is returned OR data from the only node having data is
>>> returned?
>>>
>>> Scenario 2: Read query is fired and all 3 replicas have different data
>>> with different timestamps.
>>>
>>> Options: data with latest timestamp is returned OR something else???
>>>
>>> Thanks
>>> Anuj
>>>
>>> Sent from Yahoo Mail on Android
>>> <https://overview.mail.yahoo.com/mobile/?.src=Android>
>>>
>>
>>
>>
>> --
>> Arun
>>
>
>
Re: Read Consistency
Posted by Alain RODRIGUEZ <ar...@gmail.com>.
Hi,
I do not agree with Scenario 1 result Arun,
The 2 nodes don't have the data yet are available. IMHO what happens next i
a slow read since it will have to perform read repair and coordinator will
send back the result and an 'OK' message.Consistency is not met when nor
enough nodes were up.
Agreed on scenario 2. I would add that one repair will be synchronous and
mandatory while the second depends on your read repair chance parameter on
this table and is async.
C*heers
2015-06-23 20:16 GMT+02:00 Anuj Wadehra <an...@yahoo.co.in>:
> Why would it fail and with what Thrift error? What if the data didnt exist
> on any of the nodes..query wont fail if doesnt find data..
>
> Not convinced..
>
> Sent from Yahoo Mail on Android
> <https://overview.mail.yahoo.com/mobile/?.src=Android>
> ------------------------------
> *From*:"arun sirimalla" <ar...@gmail.com>
> *Date*:Tue, 23 Jun, 2015 at 11:39 pm
> *Subject*:Re: Read Consistency
>
> Scenario 1: Read query is fired for a key, data is found on one node and
> not found on other two nodes who are responsible for the token
> corresponding to key.
>
> You read query will fail, as it expects to receive data from 2 nodes with
> RF=3
>
>
> Scenario 2: Read query is fired and all 3 replicas have different data
> with different timestamps.
>
> Read query will return the data with most recent timestamp and trigger a
> read repair in the backend .
>
> On Tue, Jun 23, 2015 at 10:57 AM, Anuj Wadehra <an...@yahoo.co.in>
> wrote:
>
>> Hi,
>>
>> Need to validate my understanding..
>>
>> RF=3 , Read CL = Quorum
>>
>> What would be returned to the client in following scenarios:
>>
>> Scenario 1: Read query is fired for a key, data is found on one node and
>> not found on other two nodes who are responsible for the token
>> corresponding to key.
>>
>> Options: no data is returned OR data from the only node having data is
>> returned?
>>
>> Scenario 2: Read query is fired and all 3 replicas have different data
>> with different timestamps.
>>
>> Options: data with latest timestamp is returned OR something else???
>>
>> Thanks
>> Anuj
>>
>> Sent from Yahoo Mail on Android
>> <https://overview.mail.yahoo.com/mobile/?.src=Android>
>>
>
>
>
> --
> Arun
>
Re: Read Consistency
Posted by Anuj Wadehra <an...@yahoo.co.in>.
Why would it fail and with what Thrift error? What if the data didnt exist on any of the nodes..query wont fail if doesnt find data..
Not convinced..
Sent from Yahoo Mail on Android
From:"arun sirimalla" <ar...@gmail.com>
Date:Tue, 23 Jun, 2015 at 11:39 pm
Subject:Re: Read Consistency
Scenario 1: Read query is fired for a key, data is found on one node and not found on other two nodes who are responsible for the token corresponding to key.
You read query will fail, as it expects to receive data from 2 nodes with RF=3
Scenario 2: Read query is fired and all 3 replicas have different data with different timestamps.
Read query will return the data with most recent timestamp and trigger a read repair in the backend .
On Tue, Jun 23, 2015 at 10:57 AM, Anuj Wadehra <an...@yahoo.co.in> wrote:
Hi,
Need to validate my understanding..
RF=3 , Read CL = Quorum
What would be returned to the client in following scenarios:
Scenario 1: Read query is fired for a key, data is found on one node and not found on other two nodes who are responsible for the token corresponding to key.
Options: no data is returned OR data from the only node having data is returned?
Scenario 2: Read query is fired and all 3 replicas have different data with different timestamps.
Options: data with latest timestamp is returned OR something else???
Thanks
Anuj
Sent from Yahoo Mail on Android
--
Arun
Re: Read Consistency
Posted by arun sirimalla <ar...@gmail.com>.
Scenario 1: Read query is fired for a key, data is found on one node and
not found on other two nodes who are responsible for the token
corresponding to key.
You read query will fail, as it expects to receive data from 2 nodes with
RF=3
Scenario 2: Read query is fired and all 3 replicas have different data with
different timestamps.
Read query will return the data with most recent timestamp and trigger a
read repair in the backend .
On Tue, Jun 23, 2015 at 10:57 AM, Anuj Wadehra <an...@yahoo.co.in>
wrote:
> Hi,
>
> Need to validate my understanding..
>
> RF=3 , Read CL = Quorum
>
> What would be returned to the client in following scenarios:
>
> Scenario 1: Read query is fired for a key, data is found on one node and
> not found on other two nodes who are responsible for the token
> corresponding to key.
>
> Options: no data is returned OR data from the only node having data is
> returned?
>
> Scenario 2: Read query is fired and all 3 replicas have different data
> with different timestamps.
>
> Options: data with latest timestamp is returned OR something else???
>
> Thanks
> Anuj
>
> Sent from Yahoo Mail on Android
> <https://overview.mail.yahoo.com/mobile/?.src=Android>
>
--
Arun