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From Anuj Wadehra <anujw_2...@yahoo.co.in>
Subject Re: Read after Write inconsistent at times
Date Sat, 25 Feb 2017 17:58:08 GMT
Hi Charulata,
Please share details on how data is being inserted and read. 
Is the client which is reading the data same as the one which inserted it? Is the read happening
only when insertion is successful? Are you using client timestamps?
How did you verify that NTP is working properly? How NTP is configured in your cluster- sample
NTP conf ?


ThanksAnuj

Sent from Yahoo Mail on Android 
 
  On Sat, 25 Feb, 2017 at 2:02 AM, Charulata Sharma (charshar)<charshar@cisco.com> wrote:
  Hi All,      Thanks for your replies. I do not see an issue with NTP or with dropped
messages.However the tombstones count on the specific CF shows me this. This essentially indicates
that there are as many tombstones as Live cells in the CF isin't?Now is that an issue and
can this cause inconsistent read ?

Average live cells per slice (last five minutes): 0.8631938498408056

Maximum live cells per slice (last five minutes): 1.0

Average tombstones per slice (last five minutes): 1.1477603751799115E-5

Maximum tombstones per slice (last five minutes): 1.0




Thanks,

Charu

From: Jonathan Haddad <jon@jonhaddad.com>
Reply-To: "user@cassandra.apache.org" <user@cassandra.apache.org>
Date: Friday, February 24, 2017 at 9:42 AM
To: "user@cassandra.apache.org" <user@cassandra.apache.org>
Subject: Re: Read after Write inconsistent at times

WRT to NTP, I first encountered this issue on my first cluster.  The problem with ntp isn't
just if you're doing inserts, it's if you're doing inserts in combination with deletes, and
using server timestamps with a greater variance than the period between the delete and the
insert.  Basically, you end up with a delete in the future and an insert in the past, and
the delete timestamp > insert timestamp.
+1 to Jan's recommendation on checking for dropped messages.


On Fri, Feb 24, 2017 at 9:35 AM Petrus Gomes <petrusgf@gmail.com> wrote:

Hi,

Check the tombstone count, If is it to high, your query will be impacted.

If tombstone is a problem, you can try to reduce your "gc_grace_seconds" to reduce tombstone
count(Carefully because you use crossdata centers).

Tchau,
Petrus Silva



On Fri, Feb 24, 2017 at 12:07 AM, Jan Kesten <j.kesten@enercast.de> wrote:

Hi,

are your nodes at high load? Are there any dropped messages (nodetool tpstats) on any node?

Also have a look at your system clocks. C* needs them in thight sync - via ntp for example.
Side hint: if you use ntp use the same set of upstreams on all of your nodes - ideal your
own one. Usingpool.ntp.org might lead to minimal dirfts in time across your cluster.

Another thing that could help you out is using client side timestamps: https://docs.datastax.com/en/developer/java-driver/3.1/manual/query_timestamps/
(of course only when you are using a single client or all clients are in sync via ntp).


Am 24.02.2017 um 07:29 schrieb Charulata Sharma (charshar):


Hi All,

In my application sometimes I cannot read data that just got inserted. This happens very intermittently.
Both write and read use LOCAL QUOROM.

We have a cluster of 12 nodes which spans across 2 Data Centers and a RF of 3.

Has anyone encountered this problem and if yes what steps have you taken to solve it

Thanks,
Charu


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