Raphael:
Have you found root cause ? If not, here are a few tips, based on what
I experienced before, but may not be same as your case, just hope it is
helpful.
1) app side called wrong code module
get the cql from system.prepared_statements
cql statement is helpful to developers to search their code and find issue
parts. In my case, was function disabled but actually not, when they see
cql statement, they realized.
2) app side code query immediately after write
from the trace, you have read time, get this row write time by
select writetime ("any non-key column here") from "table_name_here" where
...;
if read time is too close to write time, ask developers to add a sleep in
code.
while earlier phase of projects using cassandra, developers still get used
to rdbms style, forget cassandra is distributed database (i.e. in code, 10
cql statements in a logic order, they assume they will be executed in
order, but actually in distributed system, no order, last line in code may
execute 1st in cassandra cluster).
3) duplicate the case
use copy tables, testing data, by comparing the traces, duplicate the case,
so know your debug direction right or not right.
Regards,
Jim
On Sun, Aug 7, 2022 at 5:14 PM Stéphane Alleaume <crystallo...@gmail.com>
wrote:
> You're right too, this option is not new, sorry.
>
> Is this option can be useful ?
>
>
> Le dim. 7 août 2022, 22:18, Bowen Song via user <user@cassandra.apache.org>
> a écrit :
>
>> Do you mean "nodetool settraceprobability"? This is not exactly new, I
>> remember it was available on Cassandra 2.x.
>> On 07/08/2022 20:43, Stéphane Alleaume wrote:
>>
>> I think perhaps you already know but i read you can now trace only a % of
>> all queries, i will look to retrieve the name of this fonctionnality (in
>> new Cassandra release).
>>
>> Hope it will help
>> Kind regards
>> Stéphane
>>
>>
>> Le dim. 7 août 2022, 20:26, Raphael Mazelier <r...@futomaki.net> a
>> écrit :
>>
>>> > "Read repair is in the blocking read path for the query, yep"
>>>
>>> OK interesting. This is not what I understood from the documentation.
>>> And I use localOne level consistency.
>>>
>>> I enabled tracing (see in the attachment of my first msg)/ but I didn't
>>> see read repair in the trace (and btw I tried to completely disable it on
>>> my table setting both read_repair_chance and local_dc_read_repair_chance to
>>> 0).
>>>
>>> The problem when enabling trace in cqlsh is that I only get slow result.
>>> For having fast answer I need to iterate faster on my queries.
>>>
>>> I can provide again trace for analysis. I got something more readable in
>>> python.
>>>
>>> Best,
>>>
>>> --
>>>
>>> Raphael
>>>
>>>
>>> On 07/08/2022 19:30, C. Scott Andreas wrote:
>>>
>>> > but still as I understand the documentation the read repair should
>>> not be in the blocking path of a query ?
>>>
>>> Read repair is in the blocking read path for the query, yep. At quorum
>>> consistency levels, the read repair must complete before returning a result
>>> to the client to ensure the data returned would be visible on subsequent
>>> reads that address the remainder of the quorum.
>>>
>>> If you enable tracing - either for a single CQL statement that is
>>> expected to be slow, or probabilistic from the server side to catch a slow
>>> query in the act - that will help identify what’s happening.
>>>
>>> - Scott
>>>
>>> On Aug 7, 2022, at 10:25 AM, Raphael Mazelier <r...@futomaki.net>
>>> <r...@futomaki.net> wrote:
>>>
>>>
>>>
>>> Nope. And what really puzzle me is in the trace we really show the
>>> difference between queries. The fast queries only request read from one
>>> replicas, while slow queries request from multiple replicas (and not only
>>> local to the dc).
>>> On 07/08/2022 14:02, Stéphane Alleaume wrote:
>>>
>>> Hi
>>>
>>> Is there some GC which could affect coordinarir node ?
>>>
>>> Kind regards
>>> Stéphane
>>>
>>> Le dim. 7 août 2022, 13:41, Raphael Mazelier <r...@futomaki.net> a
>>> écrit :
>>>
>>>> Thanks for the answer but I was well aware of this. I use localOne as
>>>> consistency level.
>>>>
>>>> My client connect to a local seeds, then choose a local coordinator (as
>>>> far I can understand the trace log).
>>>>
>>>> Then for a batch of request I got approximately 98% of request treated
>>>> in 2/3ms in local DC with one read request, and 2% treated by many nodes
>>>> (according to the trace) and then way longer (250ms).
>>>>
>>>> ?
>>>> On 06/08/2022 14:30, Bowen Song via user wrote:
>>>>
>>>> See the diagram below. Your problem almost certainly arises from step
>>>> 4, in which an incorrect consistency level set by the client caused the
>>>> coordinator node to send the READ command to nodes in other DCs.
>>>>
>>>> The load balancing policy only affects step 2 and 3, not step 1 or 4.
>>>>
>>>> You should change the consistency level to LOCAL_ONE/LOCAL_QUORUM/etc.
>>>> to fix the problem.
>>>>
>>>> On 05/08/2022 22:54, Bowen Song wrote:
>>>>
>>>> The DCAwareRoundRobinPolicy/TokenAwareHostPolicy controlls which
>>>> Cassandra coordinator node the client sends queries to, not the nodes it
>>>> connects to, nor the nodes that performs the actual read.
>>>>
>>>> A client sends a CQL read query to a coordinator node, and the
>>>> coordinator node parses the CQL query, and send READ requests to other
>>>> nodes in the cluster based on the consistency level.
>>>>
>>>> Have you checked the consistency level of the session (and the query if
>>>> applicable)? Is it prefixed with "LOCAL_"? If not, the coordinator will
>>>> send the READ requests to non-local DCs.
>>>>
>>>>
>>>> On 05/08/2022 19:40, Raphael Mazelier wrote:
>>>>
>>>>
>>>> Hi Cassandra Users,
>>>>
>>>> I'm relatively new to Cassandra and first I have to say I'm really
>>>> impressed by the technology.
>>>>
>>>> Good design and a lot of stuff to understand the underlying (the
>>>> Oreilly book help a lot as well as thelastpickle blog post).
>>>>
>>>> I have an muli-datacenter c* cluster (US, Europe, Singapore) with eight
>>>> node on each (two seeds on each region), two racks on Eu, Singapore, 3 on
>>>> US. Everything deployed in AWS.
>>>>
>>>> We have a keyspace configured with network topology and two replicas on
>>>> every region like this: {'class': 'NetworkTopologyStrategy',
>>>> 'ap-southeast-1': '2', 'eu-west-1': '2', 'us-east-1': '2'}
>>>>
>>>>
>>>> Investigating some performance issue I noticed strange things in my
>>>> experiment:
>>>>
>>>> What we expect is very slow latency 3/5ms max for this specific select
>>>> query. So we want every read to be local the each datacenter.
>>>>
>>>> We configure DCAwareRoundRobinPolicy(local_dc=DC) in python, and the
>>>> same in Go gocql.TokenAwareHostPolicy(gocql.DCAwareRoundRobinPolicy("DC"))
>>>>
>>>> Testing a bit with two short program (I can provide them) in go and
>>>> python I notice very strange result. Basically I do the same query over and
>>>> over with a very limited dataset of id.
>>>>
>>>> The first result were surprising cause the very first query were always
>>>> more than 250ms and after with stressing c* (playing with sleep between
>>>> query) I can achieve a good ratio of query at 3/4 ms (what I expected).
>>>>
>>>> My guess was that long query were somewhat executed not locally (or at
>>>> least imply multi datacenter queries) and short one no.
>>>>
>>>> Activating tracing in my program (like enalbing trace in cqlsh) kindla
>>>> confirm my suspicion.
>>>>
>>>> (I will provide trace in attachment).
>>>>
>>>> My question is why sometime C* try to read not localy? how we can
>>>> disable it? what is the criteria for this?
>>>>
>>>> (btw I'm very not fan of this multi region design for theses very
>>>> specific kind of issues...)
>>>>
>>>> Also side question: why C* is so slow at connection? it's like it's
>>>> trying to reach every nodes in each DC? (we only provide locals seeds
>>>> however). Sometimes it take more than 20s...
>>>>
>>>> Any help appreciated.
>>>>
>>>> Best,
>>>>
>>>> --
>>>>
>>>> Raphael Mazelier
>>>>
>>>>
